actions-runner-controller (ARC)

This controller operates self-hosted runners for GitHub Actions on your Kubernetes cluster.

ToC:

People
Status
About
Installation
- GitHub Enterprise Support
Setting Up Authentication with GitHub API
- Deploying Using GitHub App Authentication
- Deploying Using PAT Authentication
Deploying Multiple Controllers
Usage
Troubleshooting
Contributing

People

actions-runner-controller is an open-source project currently developed and maintained in collaboration with maintainers @mumoshu and @toast-gear, various contributors, and the awesome community, mostly in their spare time.

If you think the project is awesome and it's becoming a basis for your important business, consider sponsoring us!

In case you are already the employer of one of contributors, sponsoring via GitHub Sponsors might not be an option. Just support them in other means!

We don't currently have any sponsors dedicated to this project yet.

However, HelloFresh has recently started sponsoring @mumoshu for this project along with his other works. A part of their sponsorship will enable @mumoshu to add an E2E test to keep ARC even more reliable on AWS. Thank you for your sponsorship!

Status

Even though actions-runner-controller is used in production environments, it is still in its early stage of development, hence versioned 0.x.

actions-runner-controller complies to Semantic Versioning 2.0.0 in which v0.x means that there could be backward-incompatible changes for every release.

The documentation is kept inline with master@HEAD, we do our best to highlight any features that require a specific ARC version or higher however this is not always easily done due to there being many moving parts. Additionally, we actively do not retain compatibly with every GitHub Enterprise Server version nor every Kubernetes version so you will need to ensure you stay current within a reasonable timespan.

About

GitHub Actions is a very useful tool for automating development. GitHub Actions jobs are run in the cloud by default, but you may want to run your jobs in your environment. Self-hosted runner can be used for such use cases, but requires the provisioning and configuration of a virtual machine instance. Instead if you already have a Kubernetes cluster, it makes more sense to run the self-hosted runner on top of it.

actions-runner-controller makes that possible. Just create a Runner resource on your Kubernetes, and it will run and operate the self-hosted runner for the specified repository. Combined with Kubernetes RBAC, you can also build simple Self-hosted runners as a Service.

Installation

By default, actions-runner-controller uses cert-manager for certificate management of Admission Webhook. Make sure you have already installed cert-manager before you install. The installation instructions for the cert-manager can be found below.

Installing cert-manager on Kubernetes

After installing cert-manager, install the custom resource definitions and actions-runner-controller with kubectl or helm. This will create an actions-runner-system namespace in your Kubernetes and deploy the required resources.

Kubectl Deployment:

# REPLACE "v0.22.0" with the version you wish to deploy
kubectl apply -f https://github.com/actions-runner-controller/actions-runner-controller/releases/download/v0.22.0/actions-runner-controller.yaml

Helm Deployment:

Configure your values.yaml, see the chart's README for the values documentation

helm repo add actions-runner-controller https://actions-runner-controller.github.io/actions-runner-controller
helm upgrade --install --namespace actions-runner-system --create-namespace \
             --wait actions-runner-controller actions-runner-controller/actions-runner-controller

GitHub Enterprise Support

The solution supports both GHEC (GitHub Enterprise Cloud) and GHES (GitHub Enterprise Server) editions as well as regular GitHub. Both PAT (personal access token) and GitHub App authentication works for installations that will be deploying either repository level and / or organization level runners. If you need to deploy enterprise level runners then you are restricted to PAT based authentication as GitHub doesn't support GitHub App based authentication for enterprise runners currently.

If you are deploying this solution into a GHES environment then you will need to be running version >= 3.3.0.

When deploying the solution for a GHES environment you need to provide an additional environment variable as part of the controller deployment:

kubectl set env deploy controller-manager -c manager GITHUB_ENTERPRISE_URL=<GHEC/S URL> --namespace actions-runner-system

Note: The repository maintainers do not have an enterprise environment (cloud or server). Support for the enterprise specific feature set is community driven and on a best effort basis. PRs from the community are welcome to add features and maintain support.

Setting Up Authentication with GitHub API

There are two ways for actions-runner-controller to authenticate with the GitHub API (only 1 can be configured at a time however):

Using a GitHub App (not supported for enterprise level runners due to lack of support from GitHub)
Using a PAT

Functionality wise, there isn't much of a difference between the 2 authentication methods. The primary benefit of authenticating via a GitHub App is an increased API quota.

If you are deploying the solution for a GHES environment you are able to configure your rate limit settings making the main benefit irrelevant. If you're deploying the solution for a GHEC or regular GitHub environment and you run into rate limit issues, consider deploying the solution using the GitHub App authentication method instead.

Deploying Using GitHub App Authentication

You can create a GitHub App for either your user account or any organization, below are the app permissions required for each supported type of runner:

Note: Links are provided further down to create an app for your logged in user account or an organization with the permissions for all runner types set in each link's query string

Required Permissions for Repository Runners:
Repository Permissions

Actions (read)
Administration (read / write)
Checks (read) (if you are going to use Webhook Driven Scaling)
Metadata (read)

Required Permissions for Organization Runners:
Repository Permissions

Actions (read)
Metadata (read)

Organization Permissions

Self-hosted runners (read / write)

Note: All API routes mapped to their permissions can be found here if you wish to review

Subscribe to events

At this point you have a choice of configuring a webhook, a webhook is needed if you are going to use webhook driven scaling. The webhook can be configured centrally in the GitHub app itself or separately. In either case the event details are:

Check run (required for all webhook driven scaling events)
Workflow job (optionally) (required for webhook driven scaling with workflow_job events

Setup Steps

If you want to create a GitHub App for your account, open the following link to the creation page, enter any unique name in the "GitHub App name" field, and hit the "Create GitHub App" button at the bottom of the page.

Create GitHub Apps on your account

If you want to create a GitHub App for your organization, replace the :org part of the following URL with your organization name before opening it. Then enter any unique name in the "GitHub App name" field, and hit the "Create GitHub App" button at the bottom of the page to create a GitHub App.

Create GitHub Apps on your organization

You will see an App ID on the page of the GitHub App you created as follows, the value of this App ID will be used later.

Download the private key file by pushing the "Generate a private key" button at the bottom of the GitHub App page. This file will also be used later.

Go to the "Install App" tab on the left side of the page and install the GitHub App that you created for your account or organization.

When the installation is complete, you will be taken to a URL in one of the following formats, the last number of the URL will be used as the Installation ID later (For example, if the URL ends in settings/installations/12345, then the Installation ID is 12345).

https://github.com/settings/installations/${INSTALLATION_ID}
https://github.com/organizations/eventreactor/settings/installations/${INSTALLATION_ID}

Finally, register the App ID (APP_ID), Installation ID (INSTALLATION_ID), and the downloaded private key file (PRIVATE_KEY_FILE_PATH) to Kubernetes as a secret.

Kubectl Deployment:

$ kubectl create secret generic controller-manager \
    -n actions-runner-system \
    --from-literal=github_app_id=${APP_ID} \
    --from-literal=github_app_installation_id=${INSTALLATION_ID} \
    --from-file=github_app_private_key=${PRIVATE_KEY_FILE_PATH}

Helm Deployment:

Configure your values.yaml, see the chart's README for deploying the secret via Helm

Deploying Using PAT Authentication

Personal Access Tokens can be used to register a self-hosted runner by actions-runner-controller.

Log-in to a GitHub account that has admin privileges for the repository, and create a personal access token with the appropriate scopes listed below:

Required Scopes for Repository Runners

repo (Full control)

Required Scopes for Organization Runners

repo (Full control)
admin:org (Full control)
admin:public_key (read:public_key)
admin:repo_hook (read:repo_hook)
admin:org_hook (Full control)
notifications (Full control)
workflow (Full control)

Required Scopes for Enterprise Runners

admin:enterprise (manage_runners:enterprise)

Note: When you deploy enterprise runners they will get access to organizations, however, access to the repositories themselves is NOT allowed by default. Each GitHub organization must allow enterprise runner groups to be used in repositories as an initial one-time configuration step, this only needs to be done once after which it is permanent for that runner group.

Note: GitHub does not document exactly what permissions you get with each PAT scope beyond a vague description. The best documentation they provide on the topic can be found here if you wish to review. The docs target OAuth apps and so are incomplete and may not be 100% accurate.

Once you have created the appropriate token, deploy it as a secret to your Kubernetes cluster that you are going to deploy the solution on:

Kubectl Deployment:

kubectl create secret generic controller-manager \
    -n actions-runner-system \
    --from-literal=github_token=${GITHUB_TOKEN}

Helm Deployment:

Configure your values.yaml, see the chart's README for deploying the secret via Helm

Deploying Multiple Controllers

This feature requires controller version => v0.18.0

Note: Be aware when using this feature that CRDs are cluster-wide and so you should upgrade all of your controllers (and your CRDs) at the same time if you are doing an upgrade. Do not mix and match CRD versions with different controller versions. Doing so risks out of control scaling.

By default the controller will look for runners in all namespaces, the watch namespace feature allows you to restrict the controller to monitoring a single namespace. This then lets you deploy multiple controllers in a single cluster. You may want to do this either because you wish to scale beyond the API rate limit of a single PAT / GitHub App configuration or you wish to support multiple GitHub organizations with runners installed at the organization level in a single cluster.

This feature is configured via the controller's --watch-namespace flag. When a namespace is provided via this flag, the controller will only monitor runners in that namespace.

You can deploy multiple controllers either in a single shared namespace, or in a unique namespace per controller.

If you plan on installing all instances of the controller stack into a single namespace there are a few things you need to do for this to work.

All resources per stack must have a unique name, in the case of Helm this can be done by giving each install a unique release name, or via the fullnameOverride properties.
authSecret.name needs to be unique per stack when each stack is tied to runners in different GitHub organizations and repositories AND you want your GitHub credentials to be narrowly scoped.
leaderElectionId needs to be unique per stack. If this is not unique to the stack the controller tries to race onto the leader election lock resulting in only one stack working concurrently. Your controller will be stuck with a log message something like this attempting to acquire leader lease arc-controllers/actions-runner-controller...
The MutatingWebhookConfiguration in each stack must include a namespace selector for that stack's corresponding runner namespace, this is already configured in the helm chart.

Alternatively, you can install each controller stack into a unique namespace (relative to other controller stacks in the cluster). Implementing ARC this way avoids the first, second and third pitfalls (you still need to set the corresponding namespace selector for each stack's mutating webhook)

Usage

GitHub self-hosted runners can be deployed at various levels in a management hierarchy:

The repository level
The organization level
The enterprise level

Runners can be deployed as 1 of 2 abstractions:

A RunnerDeployment (similar to k8s's Deployments, based on Pods)
A RunnerSet (based on k8s's StatefulSets)

We go into details about the differences between the 2 later, initially lets look at how to deploy a basic RunnerDeployment at the 3 possible management hierarchies.

Repository Runners

To launch a single self-hosted runner, you need to create a manifest file that includes a RunnerDeployment resource as follows. This example launches a self-hosted runner with name example-runnerdeploy for the actions-runner-controller/actions-runner-controller repository.

# runnerdeployment.yaml
apiVersion: actions.summerwind.dev/v1alpha1
kind: RunnerDeployment
metadata:
  name: example-runnerdeploy
spec:
  replicas: 1
  template:
    spec:
      repository: mumoshu/actions-runner-controller-ci

Apply the created manifest file to your Kubernetes.

$ kubectl apply -f runnerdeployment.yaml
runnerdeployment.actions.summerwind.dev/example-runnerdeploy created

You can see that 1 runner and its underlying pod has been created as specified by replicas: 1 attribute:

$ kubectl get runners
NAME                             REPOSITORY                             STATUS
example-runnerdeploy2475h595fr   mumoshu/actions-runner-controller-ci   Running

$ kubectl get pods
NAME                           READY   STATUS    RESTARTS   AGE
example-runnerdeploy2475ht2qbr 2/2     Running   0          1m

The runner you created has been registered directly to the defined repository, you should be able to see it in the settings of the repository.

Now you can use your self-hosted runner. See the official documentation on how to run a job with it.

Organization Runners

To add the runner to an organization, you only need to replace the repository field with organization, so the runner will register itself to the organization.

apiVersion: actions.summerwind.dev/v1alpha1
kind: RunnerDeployment
metadata:
  name: example-runnerdeploy
spec:
  replicas: 1
  template:
    spec:
      organization: your-organization-name

Now you can see the runner on the organization level (if you have organization owner permissions).

Enterprise Runners

To add the runner to an enterprise, you only need to replace the repository field with enterprise, so the runner will register itself to the enterprise.

apiVersion: actions.summerwind.dev/v1alpha1
kind: RunnerDeployment
metadata:
  name: example-runnerdeploy
spec:
  replicas: 1
  template:
    spec:
      enterprise: your-enterprise-name

Now you can see the runner on the enterprise level (if you have enterprise access permissions).

RunnerDeployments

In our previous examples we were deploying a single runner via the RunnerDeployment kind, the amount of runners deployed can be statically set via the replicas: field, we can increase this value to deploy additioanl sets of runners instead:

# runnerdeployment.yaml
apiVersion: actions.summerwind.dev/v1alpha1
kind: RunnerDeployment
metadata:
  name: example-runnerdeploy
spec:
  # This will deploy 2 runners now
  replicas: 2
  template:
    spec:
      repository: mumoshu/actions-runner-controller-ci

Apply the manifest file to your cluster:

$ kubectl apply -f runnerdeployment.yaml
runnerdeployment.actions.summerwind.dev/example-runnerdeploy created

You can see that 2 runners have been created as specified by replicas: 2:

$ kubectl get runners
NAME                             REPOSITORY                             STATUS
example-runnerdeploy2475h595fr   mumoshu/actions-runner-controller-ci   Running
example-runnerdeploy2475ht2qbr   mumoshu/actions-runner-controller-ci   Running

RunnerSets

This feature requires controller version => v0.20.0

Ensure you see the limitations before using this kind!!!!!

We can also deploy sets of RunnerSets the same way, a basic RunnerSet would look like this:

apiVersion: actions.summerwind.dev/v1alpha1
kind: RunnerSet
metadata:
  name: example
spec:
  replicas: 1
  repository: mumoshu/actions-runner-controller-ci
  # Other mandatory fields from StatefulSet
  selector:
    matchLabels:
      app: example
  serviceName: example
  template:
    metadata:
      labels:
        app: example

As it is based on StatefulSet, selector and template.metadata.labels it needs to be defined and have the exact same set of labels. serviceName must be set to some non-empty string as it is also required by StatefulSet.

Runner-related fields like ephemeral, repository, organization, enterprise, and so on should be written directly under spec.

Fields like volumeClaimTemplates that originates from StatefulSet should also be written directly under spec.

Pod-related fields like security contexts and volumes are written under spec.template.spec like StatefulSet.

Similarly, container-related fields like resource requests and limits, container image names and tags, security context, and so on are written under spec.template.spec.containers. There are two reserved container name, runner and docker. The former is for the container that runs actions runner and the latter is for the container that runs a dockerd.

For a more complex example, see the below:

apiVersion: actions.summerwind.dev/v1alpha1
kind: RunnerSet
metadata:
  name: example
spec:
  replicas: 1
  repository: mumoshu/actions-runner-controller-ci
  dockerdWithinRunnerContainer: true
  template:
    spec:
      securityContext:
        # All level/role/type/user values will vary based on your SELinux policies.
        # See https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux_atomic_host/7/html/container_security_guide/docker_selinux_security_policy for information about SELinux with containers
        seLinuxOptions:
          level: "s0"
          role: "system_r"
          type: "super_t"
          user: "system_u"
      containers:
      - name: runner
        env: []
        resources:
          limits:
            cpu: "4.0"
            memory: "8Gi"
          requests:
            cpu: "2.0"
            memory: "4Gi"
        # This is an advanced configuration. Don't touch it unless you know what you're doing.
        securityContext:
          # Usually, the runner container's privileged field is derived from dockerdWithinRunnerContainer.
          # But in the case where you need to run privileged job steps even if you don't use docker/don't need dockerd within the runner container,
          # just specified `privileged: true` like this.
          # See https://github.com/actions-runner-controller/actions-runner-controller/issues/1282
          # Do note that specifying `privileged: false` while using dind is very likely to fail, even if you use some vm-based container runtimes
          # like firecracker and kata. Basically they run containers within dedicated micro vms and so
          # it's more like you can use `privileged: true` safer with those runtimes.
          #
          # privileged: true
      - name: docker
        resources:
          limits:
            cpu: "4.0"
            memory: "8Gi"
          requests:
            cpu: "2.0"
            memory: "4Gi"

You can also read the design and usage documentation written in the original pull request that introduced RunnerSet for more information #629.

Under the hood, RunnerSet relies on Kubernetes's StatefulSet and Mutating Webhook. A statefulset is used to create a number of pods that has stable names and dynamically provisioned persistent volumes, so that each statefulset-managed pod gets the same persistent volume even after restarting. A mutating webhook is used to dynamically inject a runner's "registration token" which is used to call GitHub's "Create Runner" API.

Limitations

For autoscaling the RunnerSet kind only supports pull driven scaling or the workflow_job event for webhook driven scaling.

Persistent Runners

Every runner managed by ARC is "ephemeral" by default. The life of an ephemeral runner managed by ARC looks like this- ARC creates a runner pod for the runner. As it's an ephemeral runner, the --ephemeral flag is passed to the actions/runner agent that runs within the runner container of the runner pod.

--ephemeral is an actions/runner feature that instructs the runner to stop and de-register itself after the first job run.

Once the ephemeral runner has completed running a workflow job, it stops with a status code of 0, hence the runner pod is marked as completed, removed by ARC.

As it's removed after a workflow job run, the runner pod is never reused across multiple GitHub Actions workflow jobs, providing you a clean environment per each workflow job.

Although not generally recommended, it's possible to disable the passing of the --ephemeral flag by explicitly setting ephemeral: false in the RunnerDeployment or RunnerSet spec. When disabled, your runner becomes "persistent". A persistent runner does not stop after workflow job ends, and in this mode actions/runner is known to clean only runner's work dir after each job. Whilst this can seem helpful it creates a non-deterministic environment which is not ideal for a CI/CD environment. Between runs, your actions cache, docker images stored in the dind and layer cache, globally installed packages etc are retained across multiple workflow job runs which can cause issues that are hard to debug and inconsistent.

Persistent runners are available as an option for some edge cases however they are not preferred as they can create challenges around providing a deterministic and secure environment.

Autoscaling

Since the release of GitHub's workflow_job webhook, webhook driven scaling is the preferred way of autoscaling as it enables targeted scaling of your RunnerDeployment / RunnerSet as it includes the runs-on information needed to scale the appropriate runners for that workflow run. More broadly, webhook driven scaling is the preferred scaling option as it is far quicker compared to the pull driven scaling and is easy to set up.

If you are using controller version < v0.22.0 and you are not using GHES, and so can't set your rate limit budget, it is recommended that you use 100 replicas or fewer to prevent being rate limited.

A RunnerDeployment or RunnerSet can scale the number of runners between minReplicas and maxReplicas fields driven by either pull based scaling metrics or via a webhook event (see limitations section of RunnerSets for caveats of this kind). Whether the autoscaling is driven from a webhook event or pull based metrics it is implemented by backing a RunnerDeployment or RunnerSet kind with a HorizontalRunnerAutoscaler kind.

Important!!! If you opt to configure autoscaling, ensure you remove the replicas: attribute in the RunnerDeployment / RunnerSet kinds that are configured for autoscaling #206

Anti-Flapping Configuration

For both pull driven or webhook driven scaling an anti-flapping implementation is included, by default a runner won't be scaled down within 10 minutes of it having been scaled up.

This anti-flap configuration also has the final say on if a runner can be scaled down or not regardless of the chosen scaling method.

This delay is configurable via 2 methods:

By setting a new default via the controller's --default-scale-down-delay flag
By setting by setting the attribute scaleDownDelaySecondsAfterScaleOut: in a HorizontalRunnerAutoscaler kind's spec:.

Below is a complete basic example of one of the pull driven scaling metrics.

apiVersion: actions.summerwind.dev/v1alpha1
kind: RunnerDeployment
metadata:
  name: example-runner-deployment
spec:
  template:
    spec:
      repository: example/myrepo
---
apiVersion: actions.summerwind.dev/v1alpha1
kind: HorizontalRunnerAutoscaler
metadata:
  name: example-runner-deployment-autoscaler
spec:
  # Runners in the targeted RunnerDeployment won't be scaled down
  # for 5 minutes instead of the default 10 minutes now
  scaleDownDelaySecondsAfterScaleOut: 300
  scaleTargetRef:
    name: example-runner-deployment
    # Uncomment the below in case the target is not RunnerDeployment but RunnerSet
    #kind: RunnerSet
  minReplicas: 1
  maxReplicas: 5
  metrics:
  - type: PercentageRunnersBusy
    scaleUpThreshold: '0.75'
    scaleDownThreshold: '0.25'
    scaleUpFactor: '2'
    scaleDownFactor: '0.5'

Pull Driven Scaling

To configure webhook driven scaling see the Webhook Driven Scaling section

The pull based metrics are configured in the metrics attribute of a HRA (see snippet below). The period between polls is defined by the controller's --sync-period flag. If this flag isn't provided then the controller defaults to a sync period of 1m, this can be configured in seconds or minutes.

Be aware that the shorter the sync period the quicker you will consume your rate limit budget, depending on your environment this may or may not be a risk. Consider monitoring ARCs rate limit budget when configuring this feature to find the optimal performance sync period.

apiVersion: actions.summerwind.dev/v1alpha1
kind: HorizontalRunnerAutoscaler
metadata:
  name: example-runner-deployment-autoscaler
spec:
  scaleTargetRef:
    # Your RunnerDeployment Here
    name: example-runner-deployment
    # Uncomment the below in case the target is not RunnerDeployment but RunnerSet
    #kind: RunnerSet
  minReplicas: 1
  maxReplicas: 5
  # Your chosen scaling metrics here
  metrics: []

Metric Options:

TotalNumberOfQueuedAndInProgressWorkflowRuns

The TotalNumberOfQueuedAndInProgressWorkflowRuns metric polls GitHub for all pending workflow runs against a given set of repositories. The metric will scale the runner count up to the total number of pending jobs at the sync time up to the maxReplicas configuration.

Benefits of this metric

Supports named repositories allowing you to restrict the runner to a specified set of repositories server-side.
Scales the runner count based on the depth of the job queue meaning a 1:1 scaling of runners to queued jobs.
Like all scaling metrics, you can manage workflow allocation to the RunnerDeployment through the use of GitHub labels.

Drawbacks of this metric

A list of repositories must be included within the scaling metric. Maintaining a list of repositories may not be viable in larger environments or self-serve environments.
May not scale quickly enough for some users' needs. This metric is pull based and so the queue depth is polled as configured by the sync period, as a result scaling performance is bound by this sync period meaning there is a lag to scaling activity.
Relatively large amounts of API requests are required to maintain this metric, you may run into API rate limit issues depending on the size of your environment and how aggressive your sync period configuration is.

Example RunnerDeployment backed by a HorizontalRunnerAutoscaler:

apiVersion: actions.summerwind.dev/v1alpha1
kind: RunnerDeployment
metadata:
  name: example-runner-deployment
spec:
  template:
    spec:
      repository: example/myrepo
---
apiVersion: actions.summerwind.dev/v1alpha1
kind: HorizontalRunnerAutoscaler
metadata:
  name: example-runner-deployment-autoscaler
spec:
  scaleTargetRef:
    name: example-runner-deployment
    # IMPORTANT : If your HRA is targeting a RunnerSet you must specify the kind in the scaleTargetRef:, uncomment the below
    #kind: RunnerSet
  minReplicas: 1
  maxReplicas: 5
  metrics:
  - type: TotalNumberOfQueuedAndInProgressWorkflowRuns
    repositoryNames:
    - example/myrepo

PercentageRunnersBusy

The HorizontalRunnerAutoscaler will poll GitHub for the number of runners in the busy state which live in the RunnerDeployment's namespace, it will then scale depending on how you have configured the scale factors.

Benefits of this metric

Supports named repositories server-side the same as the TotalNumberOfQueuedAndInProgressWorkflowRuns metric #313
Supports GitHub organization wide scaling without maintaining an explicit list of repositories, this is especially useful for those that are working at a larger scale. #223
Like all scaling metrics, you can manage workflow allocation to the RunnerDeployment through the use of GitHub labels
Supports scaling desired runner count on both a percentage increase / decrease basis as well as on a fixed increase / decrease count basis #223 #315

Drawbacks of this metric

May not scale quickly enough for some users' needs. This metric is pull based and so the number of busy runners is polled as configured by the sync period, as a result scaling performance is bound by this sync period meaning there is a lag to scaling activity.
We are scaling up and down based on indicative information rather than a count of the actual number of queued jobs and so the desired runner count is likely to under provision new runners or overprovision them relative to actual job queue depth, this may or may not be a problem for you.

Examples of each scaling type implemented with a RunnerDeployment backed by a HorizontalRunnerAutoscaler:

---
apiVersion: actions.summerwind.dev/v1alpha1
kind: HorizontalRunnerAutoscaler
metadata:
  name: example-runner-deployment-autoscaler
spec:
  scaleTargetRef:
    name: example-runner-deployment
    # Uncomment the below in case the target is not RunnerDeployment but RunnerSet
    #kind: RunnerSet
  minReplicas: 1
  maxReplicas: 5
  metrics:
  - type: PercentageRunnersBusy
    scaleUpThreshold: '0.75'    # The percentage of busy runners at which the number of desired runners are re-evaluated to scale up
    scaleDownThreshold: '0.3'   # The percentage of busy runners at which the number of desired runners are re-evaluated to scale down
    scaleUpFactor: '1.4'        # The scale up multiplier factor applied to desired count
    scaleDownFactor: '0.7'      # The scale down multiplier factor applied to desired count

---
apiVersion: actions.summerwind.dev/v1alpha1
kind: HorizontalRunnerAutoscaler
metadata:
  name: example-runner-deployment-autoscaler
spec:
  scaleTargetRef:
    name: example-runner-deployment
    # Uncomment the below in case the target is not RunnerDeployment but RunnerSet
    #kind: RunnerSet
  minReplicas: 1
  maxReplicas: 5
  metrics:
  - type: PercentageRunnersBusy
    scaleUpThreshold: '0.75'    # The percentage of busy runners at which the number of desired runners are re-evaluated to scale up
    scaleDownThreshold: '0.3'   # The percentage of busy runners at which the number of desired runners are re-evaluated to scale down
    scaleUpAdjustment: 2        # The scale up runner count added to desired count
    scaleDownAdjustment: 1      # The scale down runner count subtracted from the desired count

Webhook Driven Scaling

To configure pull driven scaling see the Pull Driven Scaling section

Webhooks are processed by a separate webhook server. The webhook server receives GitHub Webhook events and scales RunnerDeployments by updating corresponding HorizontalRunnerAutoscalers.

Today, the Webhook server can be configured to respond to GitHub's check_run, workflow_job, pull_request, and push events by scaling up the matching HorizontalRunnerAutoscaler by N replica(s), where N is configurable within HorizontalRunnerAutoscaler's spec:.

More concretely, you can configure the targeted GitHub event types and the N in scaleUpTriggers:

kind: HorizontalRunnerAutoscaler
spec:
  scaleTargetRef:
    name: example-runners
    # Uncomment the below in case the target is not RunnerDeployment but RunnerSet
    #kind: RunnerSet
  scaleUpTriggers:
  - githubEvent:
      checkRun:
        types: ["created"]
        status: "queued"
    amount: 1
    duration: "5m"

With the above example, the webhook server scales example-runners by 1 replica for 5 minutes on each check_run event with the type of created and the status of queued received.

Of note is the HRA.spec.scaleUpTriggers[].duration attribute. This attribute is used to calculate if the replica number added via the trigger is expired or not. On each reconciliation loop, the controller sums up all the non-expiring replica numbers from previous scale-up triggers. It then compares the summed desired replica number against the current replica number. If the summed desired replica number > the current number then it means the replica count needs to scale up.

As mentioned previously, the scaleDownDelaySecondsAfterScaleOut property has the final say still. If the latest scale-up time + the anti-flapping duration is later than the current time, it doesn’t immediately scale down and instead retries the calculation again later to see if it needs to scale yet.

The primary benefit of autoscaling on Webhooks compared to the pull driven scaling is that it is far quicker as it allows you to immediately add runner resources rather than waiting for the next sync period.

You can learn the implementation details in #282

Install with Helm

To enable this feature, you first need to install the GitHub webhook server. To install via our Helm chart, see the values documentation for all configuration options

$ helm upgrade --install --namespace actions-runner-system --create-namespace \
             --wait actions-runner-controller actions-runner-controller/actions-runner-controller \
             --set "githubWebhookServer.enabled=true,service.type=NodePort,githubWebhookServer.ports[0].nodePort=33080"

The above command will result in exposing the node port 33080 for Webhook events. Usually, you need to create an external load balancer targeted to the node port, and register the hostname or the IP address of the external load balancer to the GitHub Webhook.

With a custom Kubernetes ingress controller:

CAUTION: The Kubernetes ingress controllers described below is just a suggestion from the community and the ARC team will not provide any user support for ingress controllers as it's not a part of this project.

The following guide on creating an ingress has been contributed by the awesome ARC community and is provided here as-is. You may, however, still be able to ask for help on the community on GitHub Discussions if you have any problems.

Kubernetes provides Ingress resources to let you configure your ingress controller to expose a Kubernetes service. If you plan to expose ARC via Ingress, you might not be required to make it a NodePort service (although nothing would prevent an ingress controller to expose NodePort services too):

$ helm upgrade --install --namespace actions-runner-system --create-namespace \
             --wait actions-runner-controller actions-runner-controller/actions-runner-controller \
             --set "githubWebhookServer.enabled=true"

The command above will create a new deployment and a service for receiving Github Webhooks on the actions-runner-system namespace.

Now we need to expose this service so that GitHub can send these webhooks over the network with TSL protection.

You can do it in any way you prefer, here we'll suggest doing it with a k8s Ingress. For the sake of this example we'll expose this service on the following URL:

https://your.domain.com/actions-runner-controller-github-webhook-server

Where your.domain.com should be replaced by your own domain.

Note: This step assumes you already have a configured cert-manager and domain name for your cluster.

Let's start by creating an Ingress file called arc-webhook-server.yaml with the following contents:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: actions-runner-controller-github-webhook-server
  namespace: actions-runner-system
  annotations:
    kubernetes.io/ingress.class: nginx
    nginx.ingress.kubernetes.io/backend-protocol: "HTTP"
spec:
  tls:
  - hosts:
    - your.domain.com
    secretName: your-tls-secret-name
  rules:
    - http:
        paths:
          - path: /actions-runner-controller-github-webhook-server
            pathType: Prefix
            backend:
              service:
                name: actions-runner-controller-github-webhook-server
                port:
                  number: 80

Make sure to set the spec.tls.secretName to the name of your TLS secret and spec.tls.hosts[0] to your own domain.

Then create this resource on your cluster with the following command:

kubectl apply -n actions-runner-system -f arc-webhook-server.yaml

Configuring GitHub for sending webhooks for our newly created webhook server:

After this step your webhook server should be ready to start receiving webhooks from GitHub.

To configure GitHub to start sending you webhooks, go to the settings page of your repository or organization then click on Webhooks, then on Add webhook.

There set the "Payload URL" field with the webhook URL you just created, if you followed the example ingress above the URL would be something like this:

https://your.domain.com/actions-runner-controller-github-webhook-server

Remember to replace your.domain.com with your own domain.

Then click on "let me select individual events" and choose Workflow Jobs.

You may also want to choose the following event(s) if you use it as a scale trigger in your HRA spec:

Check runs
Pushes
Pull Requests

Later you can remove any of these you are not using to reduce the amount of data sent to your server.

Then click on Add Webhook.

GitHub will then send a ping event to your webhook server to check if it is working, if it is you'll see a green V mark alongside your webhook on the Settings -> Webhooks page.

Once you were able to confirm that the Webhook server is ready and running from GitHub create or update your HorizontalRunnerAutoscaler resources by learning the following configuration examples.

Install with Kustomize

To install this feature using Kustomize, add github-webhook-server resources to your kustomization.yaml file as in the example below:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

resources:
# You should already have this
- github.com/actions-runner-controller/actions-runner-controller/config//default?ref=v0.22.2
# Add the below!
- github.com/actions-runner-controller/actions-runner-controller/config//github-webhook-server?ref=v0.22.2

Finally, you will have to configure an ingress so that you may configure the webhook in github. An example of such ingress can be find below:

```yaml
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: actions-runners-webhook-server
spec:
  rules:
  - http:
      paths:
      - path: /
        backend:
          service:
            name: github-webhook-server
            port:
              number: 80
        pathType: Exact

Examples

Example 1: Scale on each workflow_job event
Example 2: Scale up on each check_run event
Example 3: Scale on each pull_request event against a given set of branches
Example 4: Scale on each push event

Example 1: Scale on each `workflow_job` event

This feature requires controller version => v0.20.0

Note: GitHub does not include the runner group information of a repository in the payload of workflow_job event in the initial queued event. The runner group information is only included for workflow_job events when the job has already been allocated to a runner (events with a status of in_progress or completed). Please do raise feature requests against GitHub for this information to be included in the initial queued event if this would improve autoscaling runners for you.

The most flexible webhook GitHub offers is the workflow_job webhook, it includes the runs-on information in the payload allowing scaling based on runner labels.

This webhook should cover most people's needs, please experiment with this webhook first before considering the others.

apiVersion: actions.summerwind.dev/v1alpha1
kind: RunnerDeployment
metadata:
  name: example-runners
spec:
  template:
    spec:
      repository: example/myrepo
---
apiVersion: actions.summerwind.dev/v1alpha1
kind: HorizontalRunnerAutoscaler
metadata:
  name: example-runners
spec:
  scaleDownDelaySecondsAfterScaleOut: 300
  minReplicas: 1
  maxReplicas: 10
  scaleTargetRef:
    name: example-runners
    # Uncomment the below in case the target is not RunnerDeployment but RunnerSet
    #kind: RunnerSet
  scaleUpTriggers:
  - githubEvent:
      workflowJob: {}
    duration: "30m"

This webhook requires you to explicitly set the labels in the RunnerDeployment / RunnerSet if you are using them in your workflow to match the agents (field runs-on). Only self-hosted will be considered as included by default.

You can configure your GitHub webhook settings to only include Workflows Job events, so that it sends us three kinds of workflow_job events per a job run.

Each kind has a status of queued, in_progress and completed. With the above configuration, actions-runner-controller adds one runner for a workflow_job event whose status is queued. Similarly, it removes one runner for a workflow_job event whose status is completed. The caveat to this to remember is that this scale-down is within the bounds of your scaleDownDelaySecondsAfterScaleOut configuration, if this time hasn't passed the scale down will be deferred.

Example 2: Scale up on each `check_run` event

Note: This should work almost like https://github.com/philips-labs/terraform-aws-github-runner

To scale up replicas of the runners for example/myrepo by 1 for 5 minutes on each check_run, you write manifests like the below:

kind: RunnerDeployment
metadata:
   name: example-runners
spec:
  template:
    spec:
      repository: example/myrepo
---
kind: HorizontalRunnerAutoscaler
spec:
  minReplicas: 1
  maxReplicas: 10
  scaleTargetRef:
    name: example-runners
    # Uncomment the below in case the target is not RunnerDeployment but RunnerSet
    #kind: RunnerSet
  scaleUpTriggers:
  - githubEvent:
      checkRun:
        types: ["created"]
        status: "queued"
    amount: 1
    duration: "5m"

To scale up replicas of the runners for myorg organization by 1 for 5 minutes on each check_run, you write manifests like the below:

kind: RunnerDeployment
metadata:
   name: example-runners
spec:
  template:
    spec:
      organization: myorg
---
kind: HorizontalRunnerAutoscaler
spec:
  minReplicas: 1
  maxReplicas: 10
  scaleTargetRef:
    name: example-runners
    # Uncomment the below in case the target is not RunnerDeployment but RunnerSet
    #kind: RunnerSet
  scaleUpTriggers:
  - githubEvent:
      checkRun:
        types: ["created"]
        status: "queued"
        # Optionally restrict autoscaling to being triggered by events from specific repositories within your organization still
        # repositories: ["myrepo", "myanotherrepo"]
    amount: 1
    duration: "5m"

Example 3: Scale on each `pull_request` event against a given set of branches

To scale up replicas of the runners for example/myrepo by 1 for 5 minutes on each pull_request against the main or develop branch you write manifests like the below:

kind: RunnerDeployment
metadata:
   name: example-runners
spec:
  template:
    spec:
      repository: example/myrepo
---
kind: HorizontalRunnerAutoscaler
spec:
  minReplicas: 1
  maxReplicas: 10
  scaleTargetRef:
    name: example-runners
    # Uncomment the below in case the target is not RunnerDeployment but RunnerSet
    #kind: RunnerSet
  scaleUpTriggers:
  - githubEvent:
      pullRequest:
        types: ["synchronize"]
        branches: ["main", "develop"]
    amount: 1
    duration: "5m"

See "activity types" for the list of valid values for scaleUpTriggers[].githubEvent.pullRequest.types.

Example 4: Scale on each push event

To scale up replicas of the runners for example/myrepo by 1 for 5 minutes on each push write manifests like the below:

kind: RunnerDeployment
metadata:
   name: example-runners
spec:
  repository: example/myrepo
---
kind: HorizontalRunnerAutoscaler
spec:
  minReplicas: 1
  maxReplicas: 10
  scaleTargetRef:
    name: example-runners
    # Uncomment the below in case the target is not RunnerDeployment but RunnerSet
    #kind: RunnerSet
  scaleUpTriggers:
  - githubEvent:
      push:
    amount: 1
    duration: "5m"

Autoscaling to/from 0

This feature requires controller version => v0.19.0

The regular RunnerDeployment / RunnerSet replicas: attribute as well as the HorizontalRunnerAutoscaler minReplicas: attribute supports being set to 0.

The main use case for scaling from 0 is with the HorizontalRunnerAutoscaler kind. To scale from 0 whilst still being able to provision runners as jobs are queued we must use the HorizontalRunnerAutoscaler with only certain scaling configurations, only the below configurations support scaling from 0 whilst also being able to provision runners as jobs are queued:

TotalNumberOfQueuedAndInProgressWorkflowRuns
PercentageRunnersBusy + TotalNumberOfQueuedAndInProgressWorkflowRuns
PercentageRunnersBusy + Webhook-based autoscaling
Webhook-based autoscaling only

PercentageRunnersBusy can't be used alone as, by its definition, it needs one or more GitHub runners to become busy to be able to scale. If there isn't a runner to pick up a job and enter a busy state then the controller will never know to provision a runner to begin with as this metric has no knowledge of the job queue and is relying on using the number of busy runners as a means for calculating the desired replica count.

If a HorizontalRunnerAutoscaler is configured with a secondary metric of TotalNumberOfQueuedAndInProgressWorkflowRuns then be aware that the controller will check the primary metric of PercentageRunnersBusy first and will only use the secondary metric to calculate the desired replica count if the primary metric returns 0 desired replicas.

Webhook-based autoscaling is the best option as it is relatively easy to configure and also it can scale quickly.

Scheduled Overrides

This feature requires controller version => v0.19.0

Scheduled Overrides allows you to configure HorizontalRunnerAutoscaler so that its spec: gets updated only during a certain period of time. This feature is usually used for the following scenarios:

You want to reduce your infrastructure costs by scaling your Kubernetes nodes down outside a given period
You want to scale for scheduled spikes in workloads

The most basic usage of this feature is to set a non-repeating override:

apiVersion: actions.summerwind.dev/v1alpha1
kind: HorizontalRunnerAutoscaler
metadata:
  name: example-runner-deployment-autoscaler
spec:
  scaleTargetRef:
    name: example-runner-deployment
    # Uncomment the below in case the target is not RunnerDeployment but RunnerSet
    #kind: RunnerSet
  scheduledOverrides:
  # Override minReplicas to 100 only between 2021-06-01T00:00:00+09:00 and 2021-06-03T00:00:00+09:00
  - startTime: "2021-06-01T00:00:00+09:00"
    endTime: "2021-06-03T00:00:00+09:00"
    minReplicas: 100
  minReplicas: 1

A scheduled override without recurrenceRule is considered a one-off override, that is active between startTime and endTime. In the second scenario, it overrides minReplicas to 100 only between 2021-06-01T00:00:00+09:00 and 2021-06-03T00:00:00+09:00.

A more advanced configuration is to include a recurrenceRule in the override:

apiVersion: actions.summerwind.dev/v1alpha1
kind: HorizontalRunnerAutoscaler
metadata:
  name: example-runner-deployment-autoscaler
spec:
  scaleTargetRef:
    name: example-runner-deployment
    # Uncomment the below in case the target is not RunnerDeployment but RunnerSet
    #kind: RunnerSet
  scheduledOverrides:
  # Override minReplicas to 0 only between 0am sat to 0am mon
  - startTime: "2021-05-01T00:00:00+09:00"
    endTime: "2021-05-03T00:00:00+09:00"
    recurrenceRule:
      frequency: Weekly
      # Optional sunset datetime attribute
      # untilTime: "2022-05-01T00:00:00+09:00"
    minReplicas: 0
  minReplicas: 1

A recurring override is initially active between startTime and endTime, and then it repeatedly gets activated after a certain period of time denoted by frequency.

frequecy can take one of the following values:

Daily
Weekly
Monthly
Yearly

By default, a scheduled override repeats forever. If you want it to repeat until a specific point in time, define untilTime. The controller creates the last recurrence of the override until the recurrence's startTime is equal or earlier than untilTime.

Do ensure that you have enough slack for untilTime so that a delayed or offline actions-runner-controller is much less likely to miss the last recurrence. For example, you might want to set untilTime to M minutes after the last recurrence's startTime, so that actions-runner-controller being offline up to M minutes doesn't miss the last recurrence.

Combining Multiple Scheduled Overrides:

In case you have a more complex scenario, try writing two or more entries under scheduledOverrides.

The earlier entry is prioritized higher than later entries. So you usually define one-time overrides at the top of your list, then yearly, monthly, weekly, and lastly daily overrides.

A common use case for this may be to have 1 override to scale to 0 during the week outside of core business hours and another override to scale to 0 during all hours of the weekend.

Alternative Runners

ARC also offers a few altenrative runner options

Runner with DinD

When using the default runner, the runner pod starts up 2 containers: runner and DinD (Docker-in-Docker). ARC maintains an alternative all in one runner image with docker running in the same container as the runner. This may be prefered from a resource or complexity perspective or to be compliant with a LimitRange namespace configuration.

# dindrunnerdeployment.yaml
apiVersion: actions.summerwind.dev/v1alpha1
kind: RunnerDeployment
metadata:
  name: example-dindrunnerdeploy
spec:
  replicas: 2
  template:
    spec:
      image: summerwind/actions-runner-dind
      dockerdWithinRunnerContainer: true
      repository: mumoshu/actions-runner-controller-ci
      env: []

Runner with rootless DinD

When using the DinD runner, it assumes that the main runner is rootful, which can be problematic in a regulated or more security-conscious environment, such as co-tenanting across enterprise projects. The actions-runner-dind-rootless image runs rootless Docker inside the container as runner user. Note that this user does not have sudo access, so anything requiring admin privileges must be built into the runner's base image (like running apt to install additional software).

Runner with K8s Jobs

When using the default runner, jobs that use a container will run in docker. This necessitates privileged mode, either on the runner pod or the sidecar container

By setting the container mode, you can instead invoke these jobs using a kubernetes implementation while not executing in privileged mode.

The runner will dynamically spin up pods and k8s jobs in the runner's namespace to run the workflow, so a workVolumeClaimTemplate is required for the runner's working directory, and a service account with the appropriate permissions.

There are some limitations to this approach, mainly job containers are required on all workflows.

# runner.yaml
apiVersion: actions.summerwind.dev/v1alpha1
kind: Runner
metadata:
  name: example-runner
spec:
  repository: example/myrepo
  containerMode: kubernetes
  serviceAccountName: my-service-account
  workVolumeClaimTemplate:
    storageClassName: "my-dynamic-storage-class"
    accessModes:
    - ReadWriteOnce
    resources:
      requests:
        storage: 10Gi
  env: []

Additional Tweaks

You can pass details through the spec selector. Here's an eg. of what you may like to do:

apiVersion: actions.summerwind.dev/v1alpha1
kind: RunnerDeployment
metadata:
  name: actions-runner
  namespace: default
spec:
  replicas: 2
  template:
    metadata:
      annotations:
        cluster-autoscaler.kubernetes.io/safe-to-evict: "true"
    spec:
      priorityClassName: "high"
      nodeSelector:
        node-role.kubernetes.io/test: ""

      securityContext:
        #All level/role/type/user values will vary based on your SELinux policies.
        #See https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux_atomic_host/7/html/container_security_guide/docker_selinux_security_policy for information about SELinux with containers
        seLinuxOptions:
          level: "s0"
          role: "system_r"
          type: "super_t"
          user: "system_u"

      tolerations:
      - effect: NoSchedule
        key: node-role.kubernetes.io/test
        operator: Exists

      topologySpreadConstraints:
        - maxSkew: 1
          topologyKey: kubernetes.io/hostname
          whenUnsatisfiable: ScheduleAnyway
          labelSelector:
            matchLabels:
              runner-deployment-name: actions-runner

      repository: mumoshu/actions-runner-controller-ci
      # The default "summerwind/actions-runner" images are available at DockerHub:
      # https://hub.docker.com/r/summerwind/actions-runner
      # You can also build your own and specify it like the below:
      image: custom-image/actions-runner:latest
      imagePullPolicy: Always
      resources:
        limits:
          cpu: "4.0"
          memory: "8Gi"
        requests:
          cpu: "2.0"
          memory: "4Gi"
      # Timeout after a node crashed or became unreachable to evict your pods somewhere else (default 5mins)
      tolerations:
        - key: "node.kubernetes.io/unreachable"
          operator: "Exists"
          effect: "NoExecute"
          tolerationSeconds: 10
      # true (default) = The runner restarts after running jobs, to ensure a clean and reproducible build environment
      # false = The runner is persistent across jobs and doesn't automatically restart
      # This directly controls the behaviour of `--once` flag provided to the github runner
      ephemeral: false
      # true (default) = A privileged docker sidecar container is included in the runner pod.
      # false = A docker sidecar container is not included in the runner pod and you can't use docker.
      # If set to false, there are no privileged container and you cannot use docker.
      dockerEnabled: false
      # Optional Docker containers network MTU
      # If your network card MTU is smaller than Docker's default 1500, you might encounter Docker networking issues.
      # To fix these issues, you should setup Docker MTU smaller than or equal to that on the outgoing network card.
      # More information:
      # - https://mlohr.com/docker-mtu/
      dockerMTU: 1500
      # Optional Docker registry mirror
      # Docker Hub has an aggressive rate-limit configuration for free plans.
      # To avoid disruptions in your CI/CD pipelines, you might want to setup an external or on-premises Docker registry mirror.
      # More information:
      # - https://docs.docker.com/docker-hub/download-rate-limit/
      # - https://cloud.google.com/container-registry/docs/pulling-cached-images
      dockerRegistryMirror: https://mirror.gcr.io/
      # false (default) = Docker support is provided by a sidecar container deployed in the runner pod.
      # true = No docker sidecar container is deployed in the runner pod but docker can be used within the runner container instead. The image summerwind/actions-runner-dind is used by default.
      dockerdWithinRunnerContainer: true
      #Optional environment variables for docker container
      # Valid only when dockerdWithinRunnerContainer=false
      dockerEnv:
        - name: HTTP_PROXY
          value: http://example.com
      # Docker sidecar container image tweaks examples below, only applicable if dockerdWithinRunnerContainer = false
      dockerdContainerResources:
        limits:
          cpu: "4.0"
          memory: "8Gi"
        requests:
          cpu: "2.0"
          memory: "4Gi"
      # Additional N number of sidecar containers
      sidecarContainers:
        - name: mysql
          image: mysql:5.7
          env:
            - name: MYSQL_ROOT_PASSWORD
              value: abcd1234
          securityContext:
            runAsUser: 0
      # workDir if not specified (default = /runner/_work)
      # You can customise this setting allowing you to change the default working directory location
      # for example, the below setting is the same as on the ubuntu-18.04 image
      workDir: /home/runner/work
      # You can mount some of the shared volumes to the dind container using dockerVolumeMounts, like any other volume mounting.
      # NOTE: in case you want to use an hostPath like the following example, make sure that Kubernetes doesn't schedule more than one runner
      # per physical host. You can achieve that by setting pod anti-affinity rules and/or resource requests/limits.
      volumes:
        - name: docker-extra
          hostPath:
            path: /mnt/docker-extra
            type: DirectoryOrCreate
        - name: repo
          hostPath:
            path: /mnt/repo
            type: DirectoryOrCreate
      dockerVolumeMounts:
        - mountPath: /var/lib/docker
          name: docker-extra
      # You can mount some of the shared volumes to the runner container using volumeMounts.
      # NOTE: Do not try to mount the volume onto the runner workdir itself as it will not work. You could mount it however on a subdirectory in the runner workdir
      # Please see https://github.com/actions-runner-controller/actions-runner-controller/issues/630#issuecomment-862087323 for more information.
      volumeMounts:
        - mountPath: /home/runner/work/repo
          name: repo
      # Optional storage medium type of runner volume mount.
      # More info: https://kubernetes.io/docs/concepts/storage/volumes/#emptydir
      # "" (default) = Node's default medium
      # Memory = RAM-backed filesystem (tmpfs)
      # NOTE: Using RAM-backed filesystem gives you fastest possible storage on your host nodes.
      volumeStorageMedium: ""
      # Total amount of local storage resources required for runner volume mount.
      # The default limit is undefined.
      # NOTE: You can make sure that nodes' resources are never exceeded by limiting used storage size per runner pod.
      # You can even disable the runner mount completely by setting limit to zero if dockerdWithinRunnerContainer = true.
      # Please see https://github.com/actions-runner-controller/actions-runner-controller/pull/674 for more information.
      volumeSizeLimit: 4Gi
      # Optional name of the container runtime configuration that should be used for pods.
      # This must match the name of a RuntimeClass resource available on the cluster.
      # More info: https://kubernetes.io/docs/concepts/containers/runtime-class
      runtimeClassName: "runc"
      # This is an advanced configuration. Don't touch it unless you know what you're doing.
      containers:
      - name: runner
        # Usually, the runner container's privileged field is derived from dockerdWithinRunnerContainer.
        # But in the case where you need to run privileged job steps even if you don't use docker/don't need dockerd within the runner container,
        # just specified `privileged: true` like this.
        # See https://github.com/actions-runner-controller/actions-runner-controller/issues/1282
        # Do note that specifying `privileged: false` while using dind is very likely to fail, even if you use some vm-based container runtimes
        # like firecracker and kata. Basically they run containers within dedicated micro vms and so
        # it's more like you can use `privileged: true` safer with those runtimes.
        #
        # privileged: true

Custom Volume mounts

You can configure your own custom volume mounts. For example to have the work/docker data in memory or on NVME SSD, for i/o intensive builds. Other custom volume mounts should be possible as well, see kubernetes documentation

RAM Disk

Example how to place the runner work dir, docker sidecar and /tmp within the runner onto a ramdisk.

kind: RunnerDeployment
spec:
  template:
    spec:
      dockerVolumeMounts:
        - mountPath: /var/lib/docker
          name: docker
      volumeMounts:
        - mountPath: /tmp
          name: tmp
      volumes:
        - name: docker
          emptyDir:
            medium: Memory
        - name: work # this volume gets automatically used up for the workdir
          emptyDir:
            medium: Memory
        - name: tmp
          emptyDir:
            medium: Memory
      ephemeral: true # recommended to not leak data between builds.

NVME SSD

In this example we provide NVME backed storage for the workdir, docker sidecar and /tmp within the runner. Here we use a working example on GKE, which will provide the NVME disk at /mnt/disks/ssd0. We will be placing the respective volumes in subdirs here and in order to be able to run multiple runners we will use the pod name as a prefix for subdirectories. Also the disk will fill up over time and disk space will not be freed until the node is removed.

Beware that running these persistent backend volumes leave data behind between 2 different jobs on the workdir and /tmp with ephemeral: false.

kind: RunnerDeployment
spec:
  template:
    spec:
      env:
      - name: POD_NAME
        valueFrom:
          fieldRef:
            fieldPath: metadata.name
      dockerVolumeMounts:
      - mountPath: /var/lib/docker
        name: docker
        subPathExpr: $(POD_NAME)-docker
      - mountPath: /runner/_work
        name: work
        subPathExpr: $(POD_NAME)-work
      volumeMounts:
      - mountPath: /runner/_work
        name: work
        subPathExpr: $(POD_NAME)-work
      - mountPath: /tmp
        name: tmp
        subPathExpr: $(POD_NAME)-tmp
      dockerEnv:
      - name: POD_NAME
        valueFrom:
          fieldRef:
            fieldPath: metadata.name
      volumes:
      - hostPath:
          path: /mnt/disks/ssd0
        name: docker
      - hostPath:
          path: /mnt/disks/ssd0
        name: work
      - hostPath:
          path: /mnt/disks/ssd0
        name: tmp
    ephemeral: true # VERY important. otherwise data inside the workdir and /tmp is not cleared between builds

Docker image layers caching

Note: Ensure that the volume mount is added to the container that is running the Docker daemon.

docker stores pulled and built image layers in the daemon's (note not client) local storage area which is usually at /var/lib/docker.

By leveraging RunnerSet's dynamic PV provisioning feature and your CSI driver, you can let ARC maintain a pool of PVs that are reused across runner pods to retain /var/lib/docker.

Be sure to add the volume mount to the container that is supposed to run the docker daemon.

Be sure to trigger several workflow runs before checking if the cache is effective. ARC requires an Available PV to be reused for the new runner pod, and a PV becomes Available only after some time after the previous runner pod that was using the PV terminated. See the related discussion.

By default, ARC creates a sidecar container named docker within the runner pod for running the docker daemon. In that case, it's where you need the volume mount so that the manifest looks like:

kind: RunnerSet
metadata:
  name: example
spec:
  template:
    spec:
      containers:
      - name: docker
        volumeMounts:
        - name: var-lib-docker
          mountPath: /var/lib/docker
  volumeClaimTemplates:
  - metadata:
      name: var-lib-docker
    spec:
      accessModes:
      - ReadWriteOnce
      resources:
        requests:
          storage: 10Mi
      storageClassName: var-lib-docker

With dockerdWithinRunnerContainer: true, you need to add the volume mount to the runner container.

Go module and build caching

Go is known to cache builds under $HOME/.cache/go-build and downloaded modules under $HOME/pkg/mod. The module cache dir can be customized by setting GOMOD_CACHE so by setting it to somewhere under $HOME/.cache, we can have a single PV to host both build and module cache, which might improve Go module downloading and building time.

Be sure to trigger several workflow runs before checking if the cache is effective. ARC requires an Available PV to be reused for the new runner pod, and a PV becomes Available only after some time after the previous runner pod that was using the PV terminated. See the related discussion.

kind: RunnerSet
metadata:
  name: example
spec:
  template:
    spec:
      containers:
      - name: runner
        env:
        - name: GOMODCACHE
          value: "/home/runner/.cache/go-mod"
        volumeMounts:
        - name: cache
          mountPath: "/home/runner/.cache"
  volumeClaimTemplates:
  - metadata:
      name: cache
    spec:
      accessModes:
      - ReadWriteOnce
      resources:
        requests:
          storage: 10Mi
      storageClassName: cache

PV-backed runner work directory

ARC works by automatically creating runner pods for running actions/runner and running config.sh which you had to ran manually without ARC.

config.sh is the script provided by actions/runner to pre-configure the runner process before being started. One of the options provided by config.sh is --work, which specifies the working directory where the runner runs your workflow jobs in.

The volume and the partition that hosts the work directory should have several or dozens of GBs free space that might be used by your workflow jobs.

By default, ARC uses /runner/_work as work directory, which is powered by Kubernetes's emptyDir. emptyDir is usually backed by a directory created within a host's volume, somewhere under /var/lib/kuberntes/pods. Therefore your host's volume that is backing /var/lib/kubernetes/pods must have enough free space to serve all the concurrent runner pods that might be deployed onto your host at the same time.

So, in case you see a job failure seemingly due to "disk full", it's very likely you need to reconfigure your host to have more free space.

In case you can't rely on host's volume, consider using RunnerSet and backing the work directory with a ephemeral PV.

Kubernetes 1.23 or greater provides the support for generic ephemeral volumes, which is designed to support this exact use-case. It's defined in the Pod spec API so it isn't currently available for RunnerDeployment. RunnerSet is based on Kubernetes' StatefulSet which mostly embeds the Pod spec under spec.template.spec, so there you go.

kind: RunnerSet
metadata:
  name: example
spec:
  template:
    spec:
      containers:
      - name: runner
        volumeMounts:
        - mountPath: /runner/_work
          name: work
      - name: docker
        volumeMounts:
        - mountPath: /runner/_work
          name: work
      volumes:
      - name: work
        ephemeral:
          volumeClaimTemplate:
            spec:
              accessModes: [ "ReadWriteOnce" ]
              storageClassName: "runner-work-dir"
              resources:
                requests:
                  storage: 10Gi

Runner Labels

To run a workflow job on a self-hosted runner, you can use the following syntax in your workflow:

jobs:
  release:
    runs-on: self-hosted

When you have multiple kinds of self-hosted runners, you can distinguish between them using labels. In order to do so, you can specify one or more labels in your Runner or RunnerDeployment spec.

apiVersion: actions.summerwind.dev/v1alpha1
kind: RunnerDeployment
metadata:
  name: custom-runner
spec:
  replicas: 1
  template:
    spec:
      repository: actions-runner-controller/actions-runner-controller
      labels:
        - custom-runner

Once this spec is applied, you can observe the labels for your runner from the repository or organization in the GitHub settings page for the repository or organization. You can now select a specific runner from your workflow by using the label in runs-on:

jobs:
  release:
    runs-on: custom-runner

When using labels there are a few things to be aware of:

self-hosted is implict with every runner as this is an automatic label GitHub apply to any self-hosted runner. As a result ARC can treat all runners as having this label without having it explicitly defined in a runner's manifest. You do not need to explicitly define this label in your runner manifests (you can if you want though).
In addition to the self-hosted label, GitHub also applies a few other default labels to any self-hosted runner. The other default labels relate to the architecture of the runner and so can't be implicitly applied by ARC as ARC doesn't know if the runner is linux or windows, x64 or ARM64 etc. If you wish to use these labels in your workflows and have ARC scale runners accurately you must also add them to your runner manifests.

Runner Groups

Runner groups can be used to limit which repositories are able to use the GitHub Runner at an organization level. Runner groups have to be created in GitHub first before they can be referenced.

To add the runner to the group NewGroup, specify the group in your Runner or RunnerDeployment spec.

apiVersion: actions.summerwind.dev/v1alpha1
kind: RunnerDeployment
metadata:
  name: custom-runner
spec:
  replicas: 1
  template:
    spec:
      group: NewGroup

GitHub supports custom visibility in a Runner Group to make it available to a specific set of repositories only. By default if no GitHub authentication is included in the webhook server ARC will be assumed that all runner groups to be usable in all repositories. Currently, GitHub does not include the repository runner group membership information in the workflow_job event (or any webhook). To make the ARC "runner group aware" additional GitHub API calls are needed to find out what runner groups are visible to the webhook's repository. This behaviour will impact your rate-limit budget and so the option needs to be explicitly configured by the end user.

This option will be enabled when proper GitHub authentication options (token, app or basic auth) are provided in the webhook server and useRunnerGroupsVisibility is set to true, e.g.

githubWebhookServer:
  enabled: false
  replicaCount: 1
  useRunnerGroupsVisibility: true

Runner Entrypoint Features

Environment variable values must all be strings

The entrypoint script is aware of a few environment variables for configuring features:

apiVersion: actions.summerwind.dev/v1alpha1
kind: RunnerDeployment
metadata:
  name: example-runnerdeployment
spec:
  template:
    spec:
      env:
        # Issues a sleep command at the start of the entrypoint
        - name: STARTUP_DELAY_IN_SECONDS
          value: "2"
        # Disables the wait for the docker daemon to be available check
        - name: DISABLE_WAIT_FOR_DOCKER
          value: "true"
        # Disables automatic runner updates
        - name: DISABLE_RUNNER_UPDATE
          value: "true"

Using IRSA (IAM Roles for Service Accounts) in EKS

This feature requires controller version => v0.15.0

Similar to regular pods and deployments, you firstly need an existing service account with the IAM role associated. Create one using e.g. eksctl. You can refer to the EKS documentation for more details.

Once you set up the service account, all you need is to add serviceAccountName and fsGroup to any pods that use the IAM-role enabled service account.

For RunnerDeployment, you can set those two fields under the runner spec at RunnerDeployment.Spec.Template:

apiVersion: actions.summerwind.dev/v1alpha1
kind: RunnerDeployment
metadata:
  name: example-runnerdeploy
spec:
  template:
    spec:
      repository: USER/REO
      serviceAccountName: my-service-account
      securityContext:
        fsGroup: 1000

Software Installed in the Runner Image

Cloud Tooling
The project supports being deployed on the various cloud Kubernetes platforms (e.g. EKS), it does not however aim to go beyond that. No cloud specific tooling is bundled in the base runner, this is an active decision to keep the overhead of maintaining the solution manageable.

Bundled Software
The GitHub hosted runners include a large amount of pre-installed software packages. GitHub maintains a list in README files at https://github.com/actions/virtual-environments/tree/main/images/linux

This solution maintains a few runner images with latest aligning with GitHub's Ubuntu version, these images do not contain all of the software installed on the GitHub runners. The images contain the following subset of packages from the GitHub runners:

Basic CLI packages
git
docker
build-essentials

The virtual environments from GitHub contain a lot more software packages (different versions of Java, Node.js, Golang, .NET, etc) which are not provided in the runner image. Most of these have dedicated setup actions which allow the tools to be installed on-demand in a workflow, for example: actions/setup-java or actions/setup-node

If there is a need to include packages in the runner image for which there is no setup action, then this can be achieved by building a custom container image for the runner. The easiest way is to start with the summerwind/actions-runner image and then install the extra dependencies directly in the docker image:

FROM summerwind/actions-runner:latest

RUN sudo apt update -y \
  && sudo apt install YOUR_PACKAGE
  && sudo rm -rf /var/lib/apt/lists/*

You can then configure the runner to use a custom docker image by configuring the image field of a Runner or RunnerDeployment:

apiVersion: actions.summerwind.dev/v1alpha1
kind: Runner
metadata:
  name: custom-runner
spec:
  repository: actions-runner-controller/actions-runner-controller
  image: YOUR_CUSTOM_DOCKER_IMAGE

Using without cert-manager

Assuming you are installing in the default namespace, ensure your certificate has SANs:

webhook-service.actions-runner-system.svc
webhook-service.actions-runner-system.svc.cluster.local

It is possible to use a self-signed certificate by following a guide like this one using openssl.

Install your certificate as a TLS secret:

$ kubectl create secret tls webhook-server-cert \
  -n actions-runner-system \
  --cert=path/to/cert/file \
  --key=path/to/key/file

Set the Helm chart values as follows:

$ CA_BUNDLE=$(cat path/to/ca.pem | base64)
$ helm --upgrade install actions-runner-controller/actions-runner-controller \
  certManagerEnabled=false \
  admissionWebHooks.caBundle=${CA_BUNDLE}

Multitenancy

This feature requires controller version => v0.26.0

In a large enterprise, there might be many GitHub organizations that requires self-hosted runners. Previously, the only way to provide ARC-managed self-hosted runners in such environment was Deploying Multiple Controllers, which incurs overhead due to it requires one ARC installation per GitHub organization.

With multitenancy, you can let ARC manage self-hosted runners across organizations. It's enabled by default and the only thing you need to start using it is to set the spec.githubAPICredentialsFrom.secretRef.name fields for the following resources:

HorizontalRunnerAutoscaler
RunnerSet

Or spec.template.spec.githubAPICredentialsFrom.secretRef.name field for the following resource:

RunnerDeployment

Although not explained above, spec.githubAPICredentialsFrom fields do exist in Runner and RunnerReplicaSet. A comparable pod annotation exists for the runner pod, too. However, note that Runner, RunnerReplicaSet and runner pods are implementation details and are managed by RunnerDeployment and ARC. Usually you don't need to manually set the fields for those resources.

githubAPICredentialsFrom.secretRef.name should refer to the name of the Kubernetes secret that contains either PAT or GitHub App credentials that is used for GitHub API calls for the said resource.

Usually, you should have a set of GitHub App credentials per a GitHub organization and you would have a RunnerDeployment and a HorizontalRunnerAutoscaler per an organization runner group. So, you might end up having the following resources for each organization:

1 Kubernetes secret that contains GitHub App credentials
1 RunnerDeployment/RunnerSet and 1 HorizontalRunnerAutoscaler per Runner Group

And the RunnerDeployment/RunnerSet and HorizontalRunnerAutoscaler should have the same value for spec.githubAPICredentialsFrom.secretRef.name, which refers to the name of the Kubernetes secret.

kind: Secret
data:
  github_app_id: ...
  github_app_installation_id: ...
  github_app_private_key: ...
---
kind: RunnerDeployment
metadata:
  namespace: org1-runners
spec:
  template:
    spec:
      githubAPICredentialsFrom:
        secretRef:
          name: org1-github-app
---
kind: HorizontalRunnerAutoscaler
metadata:
  namespace: org1-runners
spec:
  githubAPICredentialsFrom:
    secretRef:
      name: org1-github-app

Do note that, as shown in the above example, you usually set the same secret name to githubAPICredentialsFrom.secretRef.name fields of both RunnerDeployment and HorizontalRunnerAutoscaler, so that GitHub API calls for the same set of runners shares the specified credentials, regardless of when and which varying ARC component(horizontalrunnerautoscaler-controller, runnerdeployment-controller, runnerreplicaset-controller, runner-controller or runnerpod-controller) makes specific API calls. Just don't be surprised you have to repeat githubAPICredentialsFrom.secretRef.name settings among two resources!

Please refer to Deploying Using GitHub App Authentication for how you could create the Kubernetes secret containing GitHub App credentials.

Troubleshooting

See troubleshooting guide for solutions to various problems people have run into consistently.

Contributing

For more details on contributing to the project (including requirements) please check out Getting Started with Contributing.

License

RjDev/actions-runner-controller

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