resources.md

PipelineResources

PipelineResources in a pipeline are the set of objects that are going to be used as inputs to a Task and can be output by a Task.

A Task can have multiple inputs and outputs.

For example:

• A Task's input could be a GitHub source which contains your application code.
• A Task's output can be your application container image which can be then deployed in a cluster.
• A Task's output can be a jar file to be uploaded to a storage bucket.

Note: PipelineResources have not been promoted to Beta in tandem with Pipeline's other CRDs. This means that the level of support for PipelineResources remains Alpha and there are effectively no guarantees about the type's future. There remain a lot of known issues with the type that have caused Tekton's developers to reassess it.

For Beta-supported alternatives to PipelineResources see the v1alpha1 to v1beta1 migration guide which lists each PipelineResource type and a suggested option for replacing it.

For more information on why PipelineResources are remaining alpha see the description of their problems, along with next steps, below.

---

• Syntax
• Using Resources
  • Variable substitution
  • Controlling where resources are mounted
  • Overriding where resources are copied from
  • Resource Status
  • Optional Resources
• Resource types
  • Git Resource
  • Pull Request Resource
  • Image Resource
  • Cluster Resource
  • Storage Resource
    • GCS Storage Resource
    • BuildGCS Storage Resource
  • Cloud Event Resource
• Why Aren't PipelineResources in Beta?

Syntax

To define a configuration file for a PipelineResource, you can specify the following fields:

• Required:
  • apiVersion - Specifies the API version, for example tekton.dev/v1alpha1.
  • kind - Specify the PipelineResource resource object.
  • metadata - Specifies data to uniquely identify the PipelineResource object, for example a name.
  • spec - Specifies the configuration information for your PipelineResource resource object.
    • type - Specifies the type of the PipelineResource
• Optional:
  • description - Description of the Resource.
  • params - Parameters which are specific to each type of PipelineResource
  • optional - Boolean flag to mark a resource optional (by default, optional is set to false making resources mandatory).

Using Resources

Resources can be used in Tasks and Conditions.

Input resources, like source code (git) or artifacts, are dumped at path /workspace/task_resource_name within a mounted volume and are available to all steps of your Task. The path that the resources are mounted at can be overridden with the targetPath field. Steps can use the pathvariable substitution key to refer to the local path to the mounted resource.

Variable substitution

Task and Condition specs can refer resource params as well as predefined variables such as path using the variable substitution syntax below where <name> is the resource's name and <key> is one of the resource's params:

In Task Spec:

For an input resource in a Task spec: shell $(resources.inputs.<name>.<key>)

Or for an output resource:

$(outputs.resources.<name>.<key>)

In Condition Spec:

Input resources can be accessed by:

$(resources.<name>.<key>)

Accessing local path to resource

The path key is predefined and refers to the local path to a resource on the mounted volume shell $(resources.inputs.<name>.path)

Controlling where resources are mounted

The optional field targetPath can be used to initialize a resource in a specific directory. If targetPath is set, the resource will be initialized under /workspace/targetPath. If targetPath is not specified, the resource will be initialized under /workspace. The following example demonstrates how git input repository could be initialized in $GOPATH to run tests:

apiVersion: tekton.dev/v1beta1
kind: Task
metadata:
  name: task-with-input
  namespace: default
spec:
  resources:
    inputs:
      - name: workspace
        type: git
        targetPath: go/src/github.com/tektoncd/pipeline
  steps:
    - name: unit-tests
      image: golang
      command: ["go"]
      args:
        - "test"
        - "./..."
      workingDir: "/workspace/go/src/github.com/tektoncd/pipeline"
      env:
        - name: GOPATH
          value: /workspace/go

Overriding where resources are copied from

When specifying input and output PipelineResources, you can optionally specify paths for each resource. paths will be used by TaskRun as the resource's new source paths i.e., copy the resource from a specified list of paths. TaskRun expects the folder and contents to be already present in specified paths. The paths feature could be used to provide extra files or altered version of existing resources before the execution of steps.

The output resource includes the name and reference to the pipeline resource and optionally paths. paths will be used by TaskRun as the resource's new destination paths i.e., copy the resource entirely to specified paths. TaskRun will be responsible for the creation of required directories and content transition. The paths feature could be used to inspect the results of TaskRun after the execution of steps.

paths feature for input and output resources is heavily used to pass the same version of resources across tasks in context of PipelineRun.

In the following example, Task and TaskRun are defined with an input resource, output resource and step, which builds a war artifact. After the execution of TaskRun(volume-taskrun), custom volume will have the entire resource java-git-resource (including the war artifact) copied to the destination path /custom/workspace/.

apiVersion: tekton.dev/v1beta1
kind: Task
metadata:
  name: volume-task
  namespace: default
spec:
  resources:
    inputs:
      - name: workspace
        type: git
    outputs:
      - name: workspace
  steps:
    - name: build-war
      image: objectuser/run-java-jar #https://hub.docker.com/r/objectuser/run-java-jar/
      command: jar
      args: ["-cvf", "projectname.war", "*"]
      volumeMounts:
        - name: custom-volume
          mountPath: /custom

apiVersion: tekton.dev/v1beta1
kind: TaskRun
metadata:
  name: volume-taskrun
  namespace: default
spec:
  taskRef:
    name: volume-task
  resources:
    inputs:
      - name: workspace
        resourceRef:
          name: java-git-resource
    outputs:
      - name: workspace
        paths:
          - /custom/workspace/
        resourceRef:
          name: java-git-resource
  podTemplate:
    volumes:
      - name: custom-volume
        emptyDir: {}

Resource Status

When resources are bound inside a TaskRun, they can include extra information in the TaskRun Status.ResourcesResult field. This information can be useful for auditing the exact resources used by a TaskRun later. Currently the Image and Git resources use this mechanism.

For an example of what this output looks like:

resourcesResult:
- key: digest
  value: sha256:a08412a4164b85ae521b0c00cf328e3aab30ba94a526821367534b81e51cb1cb
  resourceRef:
    name: skaffold-image-leeroy-web

Description

The description field is an optional field and can be used to provide description of the Resource.

Optional Resources

By default, a resource is declared as mandatory unless optional is set to true for that resource. Resources declared as optional in a Task does not have be specified in TaskRun.

apiVersion: tekton.dev/v1beta1
kind: Task
metadata:
  name: task-check-optional-resources
spec:
  resources:
    inputs:
      - name: git-repo
        type: git
        optional: true

Similarly, resources declared as optional in a Pipeline does not have to be specified in PipelineRun.

apiVersion: tekton.dev/v1beta1
kind: Pipeline
metadata:
  name: pipeline-build-image
spec:
  resources:
    - name: workspace
      type: git
      optional: true
  tasks:
    - name: check-workspace
...

You can refer to different examples demonstrating usage of optional resources in Task, Condition, and Pipeline:

• Task
• Cluster Task
• Condition
• Pipeline

Resource Types

Git Resource

The git resource represents a git repository, that contains the source code to be built by the pipeline. Adding the git resource as an input to a Task will clone this repository and allow the Task to perform the required actions on the contents of the repo.

To create a git resource using the PipelineResource CRD:

apiVersion: tekton.dev/v1alpha1
kind: PipelineResource
metadata:
  name: wizzbang-git
  namespace: default
spec:
  type: git
  params:
    - name: url
      value: https://github.com/wizzbangcorp/wizzbang.git
    - name: revision
      value: master

Params that can be added are the following:

1. url: represents the location of the git repository, you can use this to change the repo, e.g. to use a fork

2. revision: Git revision (branch, tag, commit SHA or ref) to clone. You can use this to control what commit or branch is used. git checkout is used to switch to the revision, and will result in a detached HEAD in most cases. Use refspec along with revision if you want to checkout a particular branch without a detached HEAD. If no revision is specified, the resource inspects remote repository to determine the correct default branch.

3. refspec: (Optional) specify a git refspec to pass to git-fetch. Note that if this field is specified, it must specify all refs, branches, tags, or commits required to checkout the specified revision. An additional fetch will not be run to obtain the contents of the revision field. If no refspec is specified, the value of the revision field will be fetched directly. The refspec is useful in manipulating the repository in several cases:

   • when the server does not support fetches via the commit SHA (i.e. does not have uploadpack.allowReachableSHA1InWant enabled) and you want to fetch and checkout a specific commit hash from a ref chain.

   • when you want to fetch several other refs alongside your revision (for instance, tags)

   • when you want to checkout a specific branch, the revision and refspec fields can work together to be able to set the destination of the incoming branch and switch to the branch.

     Examples:

     • Check out a specified revision commit SHA1 after fetching ref (detached)
         revision: cb17eba165fe7973ef9afec20e7c6971565bd72f
         refspec: refs/smoke/myref
       
     • Fetch all tags alongside refs/heads/master and switch to the master branch (not detached)
         revision: master
         refspec: "refs/tags/*:refs/tags/* +refs/heads/master:refs/heads/master"
       
     • Fetch the develop branch and switch to it (not detached)
         revision: develop
         refspec: refs/heads/develop:refs/heads/develop
       
     • Fetch refs/pull/1009/head into the master branch and switch to it (not detached)
         revision: master
         refspec: refs/pull/1009/head:refs/heads/master
       

4. submodules: defines if the resource should initialize and fetch the submodules, value is either true or false. If not specified, this will default to true

5. depth: performs a shallow clone where only the most recent commit(s) will be fetched. This setting also applies to submodules. If set to '0', all commits will be fetched. If not specified, the default depth is 1.

6. sslVerify: defines if http.sslVerify should be set to true or false in the global git config. Defaults to true if omitted.

When used as an input, the Git resource includes the exact commit fetched in the resourceResults section of the taskRun's status object:

resourceResults:
- key: commit
  value: 6ed7aad5e8a36052ee5f6079fc91368e362121f7
  resourceRef:
    name: skaffold-git

Using a fork

The Url parameter can be used to point at any git repository, for example to use a GitHub fork at master:

spec:
  type: git
  params:
    - name: url
      value: https://github.com/bobcatfish/wizzbang.git

Using a branch

The revision can be any git commit-ish (revision). You can use this to create a git PipelineResource that points at a branch, for example:

spec:
  type: git
  params:
    - name: url
      value: https://github.com/wizzbangcorp/wizzbang.git
    - name: revision
      value: some_awesome_feature

To point at a pull request, you can use the pull requests's branch:

spec:
  type: git
  params:
    - name: url
      value: https://github.com/wizzbangcorp/wizzbang.git
    - name: revision
      value: refs/pull/52525/head

Using HTTP/HTTPS Proxy

The httpProxy and httpsProxy parameter can be used to proxy non-SSL/SSL requests, for example to use an enterprise proxy server for SSL requests:

spec:
  type: git
  params:
    - name: url
      value: https://github.com/bobcatfish/wizzbang.git
    - name: httpsProxy
      value: "my-enterprise.proxy.com"

Using No Proxy

The noProxy parameter can be used to opt out of proxying, for example, to not proxy HTTP/HTTPS requests to no.proxy.com:

spec:
  type: git
  params:
    - name: url
      value: https://github.com/bobcatfish/wizzbang.git
    - name: noProxy
      value: "no.proxy.com"

Note: httpProxy, httpsProxy, and noProxy are all optional but no validation done if all three are specified.

Pull Request Resource

The pullRequest resource represents a pull request event from a source control system.

Adding the Pull Request resource as an input to a Task will populate the workspace with a set of files containing generic pull request related metadata such as base/head commit, comments, and labels.

The payloads will also contain links to raw service-specific payloads where appropriate.

Adding the Pull Request resource as an output of a Task will update the source control system with any changes made to the pull request resource during the pipeline.

Example file structure:

/workspace/
/workspace/<resource>/
/workspace/<resource>/labels/
/workspace/<resource>/labels/<label>
/workspace/<resource>/status/
/workspace/<resource>/status/<status>
/workspace/<resource>/comments/
/workspace/<resource>/comments/<comment>
/workspace/<resource>/head.json
/workspace/<resource>/base.json
/workspace/<resource>/pr.json

More details:

Labels are empty files, named after the desired label string.

Statuses describe pull request statuses. It is represented as a set of json files.

References (head and base) describe Git references. They are represented as a set of json files.

Comments describe a pull request comment. They are represented as a set of json files.

Other pull request information can be found in pr.json. This is a read-only resource. Users should use other subresources (labels, comments, etc) to interact with the PR.

For an example of the output this resource provides, see example.

To create a pull request resource using the PipelineResource CRD:

apiVersion: tekton.dev/v1alpha1
kind: PipelineResource
metadata:
  name: wizzbang-pr
  namespace: default
spec:
  type: pullRequest
  params:
    - name: url
      value: https://github.com/wizzbangcorp/wizzbang/pulls/1
  secrets:
    - fieldName: authToken
      secretName: github-secrets
      secretKey: token
---
apiVersion: v1
kind: Secret
metadata:
  name: github-secrets
type: Opaque
data:
  token: github_personal_access_token_secret # in base64 encoded form

Params that can be added are the following:

1. url: represents the location of the pull request to fetch.
2. provider: represents the SCM provider to use. This will be "guessed" based on the url if not set. Valid values are github or gitlab today.
3. insecure-skip-tls-verify: represents whether to skip verification of certificates from the git server. Valid values are "true" or "false", the default being "false".

Statuses

The following status codes are available to use for the Pull Request resource: https://godoc.org/github.com/jenkins-x/go-scm/scm#State

Pull Request

The pullRequest resource will look for GitHub or GitLab OAuth authentication tokens in spec secrets with a field name called authToken.

URLs should be of the form: tektoncd#1

Self hosted / Enterprise instances

The PullRequest resource works with self hosted or enterprise GitHub/GitLab instances. Simply provide the pull request URL and set the provider parameter. If you need to skip certificate validation set the insecure-skip-tls-verify parameter to "true".

apiVersion: tekton.dev/v1alpha1
kind: PipelineResource
metadata:
  name: wizzbang-pr
  namespace: default
spec:
  type: pullRequest
  params:
    - name: url
      value: https://github.example.com/wizzbangcorp/wizzbang/pulls/1
    - name: provider
      value: github

Image Resource

An image resource represents an image that lives in a remote repository. It is usually used as a Task output for Tasks that build images. This allows the same Tasks to be used to generically push to any registry.

Params that can be added are the following:

1. url: The complete path to the image, including the registry and the image tag
2. digest: The image digest which uniquely identifies a particular build of an image with a particular tag. While this can be provided as a parameter, there is not yet a way to update this value after an image is built, but this is planned in #216.

For example:

apiVersion: tekton.dev/v1alpha1
kind: PipelineResource
metadata:
  name: kritis-resources-image
  namespace: default
spec:
  type: image
  params:
    - name: url
      value: gcr.io/staging-images/kritis

Surfacing the image digest built in a task

To surface the image digest in the output of the taskRun the builder tool should produce this information in a OCI Image Layout index.json file. This file should be placed on a location as specified in the task definition under the default resource directory, or the specified targetPath. If there is only one image in the index.json file, the digest of that image is exported; otherwise, the digest of the whole image index would be exported. For example this build-push task defines the outputImageDir for the builtImage resource in /workspace/buildImage

apiVersion: tekton.dev/v1beta1
kind: Task
metadata:
  name: build-push
spec:
  resources:
    inputs:
      - name: workspace
        type: git
    outputs:
      - name: builtImage
        type: image
        targetPath: /workspace/builtImage
  steps: ...

If no value is specified for targetPath, it will default to /workspace/output/{resource-name}.

Please check the builder tool used on how to pass this path to create the output file.

The taskRun will include the image digest in the resourcesResult field that is part of the taskRun.Status

for example:

status:
    ...
    resourcesResult:
    - key: "digest"
      value: "sha256:eed29cd0b6feeb1a92bc3c4f977fd203c63b376a638731c88cacefe3adb1c660"
      resourceRef:
        name: skaffold-image-leeroy-web
    ...

If the index.json file is not produced, the image digest will not be included in the taskRun output.

Cluster Resource

A cluster resource represents a Kubernetes cluster other than the current cluster Tekton Pipelines is running on. A common use case for this resource is to deploy your application/function on different clusters.

The resource will use the provided parameters to create a kubeconfig file that can be used by other steps in the pipeline Task to access the target cluster. The kubeconfig will be placed in /workspace/<your-cluster-name>/kubeconfig on your Task container

The Cluster resource has the following parameters:

• url (required): Host url of the master node
• username (required): the user with access to the cluster
• password: to be used for clusters with basic auth
• namespace: The namespace to target in the cluster
• token: to be used for authentication, if present will be used ahead of the password
• insecure: to indicate server should be accessed without verifying the TLS certificate.
• cadata (required): holds PEM-encoded bytes (typically read from a root certificates bundle).
• clientKeyData: contains PEM-encoded data from a client key file for TLS
• clientCertificateData: contains PEM-encoded data from a client cert file for TLS

Note: Since only one authentication technique is allowed per user, either a token or a password should be provided, if both are provided, the password will be ignored.

clientKeyData and clientCertificateData are only required if token or password is not provided for authentication to cluster.

The following example shows the syntax and structure of a cluster resource:

apiVersion: tekton.dev/v1alpha1
kind: PipelineResource
metadata:
  name: test-cluster
spec:
  type: cluster
  params:
    - name: url
      value: https://10.10.10.10 # url to the cluster master node
    - name: cadata
      value: LS0tLS1CRUdJTiBDRVJ.....
    - name: token
      value: ZXlKaGJHY2lPaU....

For added security, you can add the sensitive information in a Kubernetes Secret and populate the kubeconfig from them.

For example, create a secret like the following example:

apiVersion: v1
kind: Secret
metadata:
  name: target-cluster-secrets
data:
  cadatakey: LS0tLS1CRUdJTiBDRVJUSUZ......tLQo=
  tokenkey: ZXlKaGJHY2lPaUpTVXpJMU5pSXNJbX....M2ZiCg==

and then apply secrets to the cluster resource

apiVersion: tekton.dev/v1alpha1
kind: PipelineResource
metadata:
  name: test-cluster
spec:
  type: cluster
  params:
    - name: url
      value: https://10.10.10.10
    - name: username
      value: admin
  secrets:
    - fieldName: token
      secretKey: tokenKey
      secretName: target-cluster-secrets
    - fieldName: cadata
      secretKey: cadataKey
      secretName: target-cluster-secrets

Example usage of the cluster resource in a Task, using variable substitution:

apiVersion: tekton.dev/v1beta1
kind: Task
metadata:
  name: deploy-image
  namespace: default
spec:
  resources:
    inputs:
      - name: workspace
        type: git
      - name: dockerimage
        type: image
      - name: testcluster
        type: cluster
  steps:
    - name: deploy
      image: image-with-kubectl
      command: ["bash"]
      args:
        - "-c"
        - kubectl --kubeconfig
          /workspace/$(resources.inputs.testcluster.name)/kubeconfig --context
          $(resources.inputs.testcluster.name) apply -f /workspace/service.yaml'

To use the cluster resource with Google Kubernetes Engine, you should use the cadata authentication mechanism.

To determine the caData, you can use the following gcloud commands:

gcloud container clusters describe <cluster-name> --format='value(masterAuth.clusterCaCertificate)'

To create a secret with this information, you can use:

CADATA=$(gcloud container clusters describe <cluster-name> --format='value(masterAuth.clusterCaCertificate)')
kubectl create secret generic cluster-ca-data --from-literal=cadata=$CADATA

To retrieve the URL, you can use this gcloud command:

gcloud container clusters describe <cluster-name> --format='value(endpoint)'

Then to use these in a resource, reference the cadata from the secret you created above, and use the IP address from the gcloud command as your url (prefixed with https://):

spec:
  type: cluster
  params:
    - name: url
      value: https://<ip address determined above>
  secrets:
    - fieldName: cadata
      secretName: cluster-ca-data
      secretKey: cadata

Storage Resource

The storage resource represents blob storage, that contains either an object or directory. Adding the storage resource as an input to a Task will download the blob and allow the Task to perform the required actions on the contents of the blob.

Only blob storage type Google Cloud Storage(gcs) is supported as of now via GCS storage resource and BuildGCS storage resource.

GCS Storage Resource

The gcs storage resource points to Google Cloud Storage blob.

To create a GCS type of storage resource using the PipelineResource CRD:

apiVersion: tekton.dev/v1alpha1
kind: PipelineResource
metadata:
  name: wizzbang-storage
  namespace: default
spec:
  type: storage
  params:
    - name: type
      value: gcs
    - name: location
      value: gs://some-bucket
    - name: dir
      value: "y" # This can have any value to be considered "true"

Params that can be added are the following:

1. location: represents the location of the blob storage.

2. type: represents the type of blob storage. For GCS storage resource this value should be set to gcs.

3. dir: represents whether the blob storage is a directory or not. By default a storage artifact is not considered a directory.

   • If the artifact is a directory then -r(recursive) flag is used, to copy all files under the source directory to a GCS bucket. Eg: gsutil cp -r source_dir/* gs://some-bucket
   • If an artifact is a single file like a zip or tar, then the copy will be only 1 level deep(not recursive). It will not trigger a copy of sub directories in the source directory. Eg: gsutil cp source.tar gs://some-bucket.tar.

Private buckets can also be configured as storage resources. To access GCS private buckets, service accounts with correct permissions are required. The secrets field on the storage resource is used for configuring this information. Below is an example on how to create a storage resource with a service account.

1. Refer to the official documentation on how to create service accounts and configuring IAM permissions to access buckets.

2. Create a Kubernetes secret from a downloaded service account json key

   kubectl create secret generic bucket-sa --from-file=./service_account.json

3. To access the GCS private bucket environment variable GOOGLE_APPLICATION_CREDENTIALS should be set, so apply the above created secret to the GCS storage resource under the fieldName key.

   apiVersion: tekton.dev/v1alpha1
   kind: PipelineResource
   metadata:
     name: wizzbang-storage
     namespace: default
   spec:
     type: storage
     params:
       - name: type
         value: gcs
       - name: location
         value: gs://some-private-bucket
       - name: dir
         value: "y"
     secrets:
       - fieldName: GOOGLE_APPLICATION_CREDENTIALS
         secretName: bucket-sa
         secretKey: service_account.json

---

BuildGCS Storage Resource

The build-gcs storage resource points to a Google Cloud Storage blob like GCS Storage Resource, either in the form of a .zip archive, or based on the contents of a source manifest file.

In addition to fetching an .zip archive, BuildGCS also unzips it.

A Source Manifest File is a JSON object, which is listing other objects in a Cloud Storage that should be fetched. The format of the manifest is a mapping of the destination file path to the location in a Cloud Storage, where the file's contents can be found. The build-gcs resource can also do incremental uploads of sources via the Source Manifest File.

To create a build-gcs type of storage resource using the PipelineResource CRD:

apiVersion: tekton.dev/v1alpha1
kind: PipelineResource
metadata:
  name: build-gcs-storage
  namespace: default
spec:
  type: storage
  params:
    - name: type
      value: build-gcs
    - name: location
      value: gs://build-crd-tests/rules_docker-master.zip
    - name: artifactType
      value: Archive

Params that can be added are the following:

1. location: represents the location of the blob storage.
2. type: represents the type of blob storage. For BuildGCS, this value should be set to build-gcs
3. artifactType: represent the type of gcs resource. Right now, we support following types:

• ZipArchive:
  • ZipArchive indicates that the resource fetched is an archive file in the zip format.
  • It unzips the archive and places all the files in the directory, which is set at runtime.
  • Archive is also supported and is equivalent to ZipArchive, but is deprecated.
• TarGzArchive:
  • TarGzArchive indicates that the resource fetched is a gzipped archive file in the tar format.
  • It unzips the archive and places all the files in the directory, which is set at runtime.
• Manifest:
  • Manifest indicates that the resource should be fetched using a source manifest file.

Private buckets other than the ones accessible by a TaskRun Service Account can not be configured as storage resources for the build-gcs storage resource right now. This is because the container image gcr.io/cloud-builders//gcs-fetcher does not support configuring secrets.

Cloud Event Resource

The cloudevent resource represents a cloud event that is sent to a target URI upon completion of a TaskRun. The cloudevent resource sends Tekton specific events; the body of the event includes the entire TaskRun spec plus status; the types of events defined for now are:

• dev.tekton.event.task.unknown
• dev.tekton.event.task.successful
• dev.tekton.event.task.failed

cloudevent resources are useful to notify a third party upon the completion and status of a TaskRun. In combinations with the Tekton triggers project they can be used to link Task/PipelineRuns asynchronously.

To create a CloudEvent resource using the PipelineResource CRD:

apiVersion: tekton.dev/v1alpha1
kind: PipelineResource
metadata:
  name: event-to-sink
spec:
  type: cloudEvent
  params:
  - name: targetURI
    value: http://sink:8080

The content of an event is for example:

Context Attributes,
  SpecVersion: 0.2
  Type: dev.tekton.event.task.successful
  Source: /apis/tekton.dev/v1beta1/namespaces/default/taskruns/pipeline-run-api-16aa55-source-to-image-task-rpndl
  ID: pipeline-run-api-16aa55-source-to-image-task-rpndl
  Time: 2019-07-04T11:03:53.058694712Z
  ContentType: application/json
Transport Context,
  URI: /
  Host: my-sink.default.my-cluster.containers.appdomain.cloud
  Method: POST
Data,
  {
    "taskRun": {
      "metadata": {...}
      "spec": {
        "inputs": {...}
        "outputs": {...}
        "serviceAccount": "default",
        "taskRef": {
          "name": "source-to-image",
          "kind": "Task"
        },
        "timeout": "1h0m0s"
      },
      "status": {...}
    }
  }

Why Aren't PipelineResources in Beta?

The short answer is that they're not ready to be given a Beta level of support by Tekton's developers. The long answer is, well, longer:

• Their behaviour can be opaque.

  They're implemented as a mixture of injected Task Steps, volume configuration and type-specific code in Tekton Pipeline's controller. This means errors from PipelineResources can manifest in quite a few different ways and it's not always obvious whether an error directly relates to PipelineResource behaviour. This problem is compounded by the fact that, while our docs explain each Resource type's "happy path", there never seems to be enough info available to explain error cases sufficiently.

• When they fail they're difficult to debug.

  Several PipelineResources inject their own Steps before a Task's Steps. It's extremely difficult to manually insert Steps before them to inspect the state of a container before they run.

• There aren't enough of them.

  The six types of existing PipelineResources only cover a tiny subset of the possible systems and side-effects we want to support with Tekton Pipelines.

• Adding extensibility to them makes them really similar to Tasks:

  • User-definable Steps? This is what Tasks provide.
  • User-definable params? Tasks already have these.
  • User-definable "resource results"? Tasks have Task Results.
  • Sharing data between Tasks using PVCs? workspaces provide this for Tasks.

• They make Tasks less reusable.

  • A Task has to choose the type of PipelineResource it will accept.
  • If a Task accepts a git PipelineResource then it's not able to accept a gcs PipelineResource from a TaskRun or PipelineRun even though both the git and gcs PipelineResources fetch files. They should technically be interchangeable: all they do is write files from somewhere remote onto disk. Yet with the existing PipelineResources implementation they aren't interchangeable.

They also present challenges from a documentation perspective:

• Their purpose is ambiguous and it's difficult to articulate what the CRD is precisely for.
• Four of the types interact with external systems (git, pull-request, gcs, gcs-build).
• Five of them write files to a Task's disk (git, pull-request, gcs, gcs-build, cluster).
• One tells the Pipelines controller to emit CloudEvents to a specific endpoint (cloudEvent).
• One writes config to disk for a Task to use (cluster).
• One writes a digest in one Task and then reads it back in another Task (image).
• Perhaps the one thing you can say about the PipelineResource CRD is that it can create side-effects for your Tasks.

What's still missing

So what are PipelineResources still good for? We think we've identified some of the most important things:

1. You can augment Task-only workflows with PipelineResources that, without them, can only be done with Pipelines.
   • For example, let's say you want to checkout a git repo for your Task to test. You have two options. First, you could use a git PipelineResource and add it directly to your test Task. Second, you could write a Pipeline that has a git-clone Task which checks out the code onto a PersistentVolumeClaim workspace and then passes that PVC workspace to your test Task. For a lot of users the second workflow is totally acceptable but for others it isn't. Some of the most noteable reasons we've heard are:
     • Some users simply cannot allocate storage on their platform, meaning PersistentVolumeClaims are out of the question.
     • Expanding a single Task workflow into a Pipeline is labor-intensive and feels unnecessary.
2. Despite being difficult to explain the whole CRD clearly each individual type is relatively easy to explain.
   • For example, users can build a pretty good "hunch" for what a git PipelineResource is without really reading any docs.
3. Configuring CloudEvents to be emitted by the Tekton Pipelines controller.
   • Work is ongoing to get notifications support into the Pipelines controller which should hopefully be able to replace the cloudEvents PipelineResource.

For each of these there is some amount of ongoing work or discussion. It may be that PipelineResources can be redesigned to fix all of their problems or it could be that the best features of PipelineResources can be extracted for use everywhere in Tekton Pipelines. So given this state of affairs PipelineResources are being kept out of beta until those questions are resolved.

For Beta-supported alternatives to PipelineResources see the v1alpha1 to v1beta1 migration guide which lists each PipelineResource type and a suggested option for replacing it.

Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 4.0 License, and code samples are licensed under the Apache 2.0 License.