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Replacement of Halyard

Status Proposed, Accepted, Implemented, Obsolete
RFC # 89
Author(s) Eric Zimanyi (@ezimanyi)
SIG / WG Kubernetes SIG

Overview

The current recommended way to deploy Spinnaker is by using Halyard. While Halyard has greatly simplified some aspects of installing and configuring Spinnaker, it has a number of shortcomings that are particularly apparent when deploying to Kubernetes. This document proposes replacing Halyard with a smaller tool called kleat that integrates better into the Kubernetes ecosystem.

Goals and Non-Goals

Goals:

  • Improve the install process for users deploying to Kubernetes by providing an install path that is Kubernetes-native and integrates well with the Kubernetes ecosystem
  • Reduce the maintenance burden of Halyard, in particular by reducing the toil required to support new configuration parameters

Non-goals:

  • This document focuses primarily on the motivation behind replacing Halyard with a smaller tool as well as the broad design and surface of of this tool. A more detailed technical design of this tool is not in scope for this document.
  • While this document focuses on making the experience of deploying Spinnaker to Kubernetes easier, it does not intend to deprecate or eliminate the ability to deploy Spinnaker to other platforms.

Motivation and Rationale

The primary purpose of Halyard is to simplify the process of configuring, updating, and operating Spinnaker.

Without Halyard, installing Spinnaker involves:

  • Determining the version of each microservice you’d like to deploy. In general, this would involve picking a top-level Spinnaker version (ex: 1.16.1) and looking up the version of each microservice tied to that top-level version.
  • Writing a service.yml config file for each microservice containing the configuration you want for your Spinnaker installation, and copy it to the correct directory.
    • The configuration parameters accepted by each microservice are in general not well documented, so writing these config files would require a fairly detailed understanding of each microservice.

Installing to a Kubernetes cluster has the additional complexity of:

  • Adding each service’s config file as a ConfigMap to your cluster
  • Adding any files referenced in the service configs as ConfigMaps or Secrets to the cluster.
  • Writing a workload (Deployment/ReplicaSet) manifest for each microservice, making sure to mount the appropriate configuration into each workload.
  • Writing a Service for any workloads (deck, gate) that should be exposed outside of the cluster.

With Halyard, this process is greatly simplified. In particular, a user can install Spinnaker to Kubernetes via:

  • Configuring Halyard with the top-level Spinnaker version to install, without needing to know about the individual microservice versions
  • Adding all configuration parameters to a single config file, either by editing the YAML directly or by running hal config commands
  • Running hal deploy apply to deploy Spinnaker

While Halyard has greatly simplified the install process, it has a number of shortcomings.

Not Kubernetes Native

As Spinnaker positions itself as a Kubernetes-native deployment tool, operators are expecting to deploy and operate Spinnaker using the same Kubernetes-native tools they use for other software. In particular, the workflow for updating Spinnaker using Halyard is to SSH to a VM (or a pod) and run a series of imperative commands. Halyard's client/server nature does not lend itself well to GitOps or Infrastructure as Code workflows; while some users have worked around this, the process is error prone and difficult to automate.

The desire for a Kubernetes-native path to install Spinnaker has led to a number of alternate install paths built on top of Halyard:

  • A Helm chart that installs Halyard as a stateful set
    • While this has provided a Kubernetes-native way of installing Halyard, the process of running and maintaining Spinnaker itself still involves SSH’ing to the Halyard pod and running imperative commands
  • An operator built by OpsMx
    • This operator appears to have many of the same drawbacks as the Helm chart, in that it will initially configure a Spinnaker installation but many customizations still involve SSH’ing to a Halyard pod and running imperative commands.
  • An operator built by Armory
    • This operator removes the need for users to run imperative commands to manage Spinnaker. It allows users to configure Spinnaker via CRUD on a SpinnakerService CRD that contains the full Halyard configuration, with the operator handling any redeployments from those changes.
    • While much of the surface area of Halyard is hidden from users of this operator, it is still built on top of Halyard.

Duplication of Kubernetes-native tools

Users often have requirements for customizing the Kubernetes objects that comprise a Spinnaker installation. For example, a common use case is to add a toleration to some/all of the workloads so that they can run on specific node pools.

As Halyard is responsible for both generating and deploying the YAML for all the Kubernetes objects that comprise a Spinnaker installation, Halyard needs to handle any customization that users want to apply. Maintaining all of these possible customizations in Halyard adds a maintenance burden, as users frequently open pull requests to add additional fields they would like on their deployments/services. Changes to the templates that generate the YAML Halyard deploys are among the most frequent causes of bugs, as there is no test coverage on these files and the templating language (Jinja) is often not familiar to contributors.

The problem of taking a set of YAML files that constitute a software installation, and customizing them with various overrides is one that has numerous solutions in the Kubernetes community, the most notable being Helm and Kustomize. Ideally, Halyard would not duplicate functionality that has existing solutions with much higher adoption; this would reduce both the maintenance burden on Halyard and the barrier to entry to Spinnaker for users familiar with these tools.

Dynamic configuration

Recently, some Spinnaker microservices have been updated to enable the use of dynamic configuration sources, leveraging Spring’s Cloud Config project. In order to use this feature, users need the raw YAML config for the individual service in a config source supported by Cloud Config. The current paradigm of using Halyard to both generate and deploy config does not fit well with this workflow, where users need to separately store their service configuration.

Incompatibility with Kubernetes-native tools

There is currently no easy way to install/manage Spinnaker using either Helm or Kustomize (excluding the above-mentioned Helm chart that effectively just installs Halyard). The root cause is the duplication of functionality in the prior section; as Halyard generates and applies YAML, there is no intermediate representation that users can customize using these tools.

While the Armory operator provides a viable Kubernetes-native way to install Spinnaker, there is still no Kubernetes-native install path for users who won’t want or need an operator. Ideally it would be reasonably easy to write a Helm chart and/or Kustomization that installs Spinnaker’s microservices and is managed using idiomatic patterns.

Complexity of implementation

Halyard is the third-largest of Spinnaker’s microservices by lines of code, comprising 55435 lines of Java code. There is minimal test code, totalling 3094 lines of Java and Groovy code. The poor test coverage, combined with heavy use of reflection and unchecked casts make refactoring difficult.

Halyard also consumes many of the other microservices as libraries. In general, engineers modifying the other microservices don’t expect that they are modifying a library consumed by other microservices. This has led to cases where changes to clouddriver or front50 led to breaking Halyard when trying to bump the dependency.

As a representative example of the amount of code change required to add a new config parameter to Halyard, consider the PR to add Google Pubsub config. This is a fairly representative example of a config parameter; it supports add/edit/delete/get/list on a list of Google Pubsub subscriptions, and required 2244 lines of code to implement (none of which is test code).

The amount of code necessary to add simple config parameters is a burden both on contributors and on the maintainers of Halyard who have to review this code. This has led to Halyard’s config often lagging behind that of the individual microservices. Ideally, adding a config parameter would be a reasonably simple first contribution for someone looking to get involved with the project, but that is currently very far from the case.

Timeline

  • Spinnaker 1.21 (June 2020)
    • An alpha version of kleat is released along with documentation, and is able to generate service configurations from the Halyard config.
    • A simple Kustomize kustomization is released that can deploy Spinnaker to Kubernetes in simple cases.
  • Spinnaker 1.22 (August 2020)
    • Feedback from early users of kleat and the kustomization are addressed, and the kustomization now supports more advanced use cases
    • The Armory operator is moved to depend on kleat
  • Spinnaker 1.23 (October 2020)
    • Kleat, as well as the kustomize install path are GA and the recommended install path for new users of Spinnaker.
    • Documentation (such as install documentation) referencing old Halyard commands is updated to reference kleat.
    • Based on adoption of kleat, a plan is formulated around how and when to deprecate and cease support of Halyard. The details of this plan will be a separate RFC.

Design

Removed and replaced features

Commands to edit the Halyard config

There are currently two ways to update the Halyard configuration:

  • Edit the YAML directly
  • Run hal … commands to update the config

YAML is ubiquitous in the Kubernetes world, and Kubernetes-native tools generally assume that users are comfortable writing YAML configuration files. As such, the value in providing a CLI that hides YAML from users is questionable, and may even contribute to the perception that Spinnaker (or at least its installation) is not Kubernetes-native. The CLI also encourages an imperative workflow whereby configuration is achieved via a series hal commands. Furthermore, a significant amount of the complexity and verbosity of Halyard’s codebase comes from the commands to edit the Halyard configuration.

Based on these considerations, the CLI commands to edit the configuration will be removed. As the hal command reference is the best existing documentation on the available config parameters for Spinnaker, it will be replaced by extensive documentation of a well-typed Halyard configuration so that users can be confident directly editing this config.

Generation and application of Kubernetes YAML

As discussed above, Halyard’s functionality to generate and apply Kubernetes YAML duplicates functionality in existing tools and makes it incompatible with these tools. It also makes it impossible for users to customize their deployments without making code changes to Halyard to account for these customizations.

For these reasons, Halyard will no longer handle generating and deploying Kubernetes YAML. Instead, Halyard will focus on generating the service configs from the Halyard config. We’ll provide a Helm chart and/or Kustomization that consumes these service configs and generates/applies YAML to the cluster.

Input validation

Halyard currently does fairly strict validation of input when using the CLI; in addition to validating the well-formedness of parameters, in some cases it also uses the code from the other services to attempt to perform operations using the parameters. (For example, when configuring a Google Compute account, Halyard will try to make a test request to list instances during its validation step.)

The value of this validation is not clear when Halyard is running on a different machine than the microservice in question. In many cases, network policies or firewalls prevent the Halyard instance from communicating with external services that individual microservices do have access to.

Halyard will reduce the scope of its validation efforts. It will focus on validating the well-formedness of the Halyard config, but will no longer act as the other microservices to try to actually build instances of credentials and make requests using them. Validating the well-formedness of the config will involve both:

  • Validating the structure of the config
  • Performing simple validation on the values supplied in the config, such as ensuring that a value is an integer or a valid URL

Secret management

Spinnaker now supports two ways of handling secrets in config files:

  • Secrets encrypted using the Spinnaker-specific format supported by kork-secrets. Halyard is able to decrypt these secrets, and in some cases (ex: deck) writes unencrypted values to services.
  • Support in the services themselves (via Spring Cloud Config) to decrypt externally-stored secrets

Halyard will no longer support decrypting secrets; users can continue to use either secret encryption method with two exceptions:

  • Halyard will no longer write unencrypted secrets to deck's config. Given that these are effectively not secrets once Halyard has written the unencrypted value to disk, users can store the unencrypted values directly in the Halyard config until deck supports decryption of encrypted secrets.
  • Halyard will no longer decrypt secrets for the purpose of validating the config; a reduction of the scope of Halyard's validation is discussed in more detail in the previous section.

Config backup/restore

Halyard has functionality to backup the entire configuration to an archive file, and to restore from such an archive file. This is useful either for backup purposes, or to copy configuration from one Halyard installation to another.

In general, the canonical solution for backing up and tracking changes to configuration in a Kubernetes-native world is to store this configuration in a git repository. To avoid duplicating existing solutions, Halyard will no longer have built-in support for backing up and restoring the configuration; it will instead presume that the operator is using some external tool to version and back up the configuration.

Version publishing/deprecating

Halyard handles publishing and deprecating Spinnaker versions; this functionality is only used by maintainers of the project and requires having a GCP service account with write permissions to the GCS bucket that stores Spinnaker version info. It is possible to use this functionality to publish custom BOMs to a private GCS bucket, so users who publish and consume custom BOMs may also be using these commands.

To simplify the surface area for end users, this functionality will be removed from Halyard and migrated to a separate admin-specific tool to handle these changes. Any users that are using the hal admin commands to publish custom BOMs will need to migrate to the new tool; given that users publishing a custom BOM are in general advanced users, this should not be a difficult migration. (More research will also be done at that stage to determine if there are even any end-users relying on these commands as part of their custom BOM workflow.)

Retained core competency

Having outlined the features to be removed from Halyard above, this section will outline the remaining core competency of Halyard.

Halyard will focus on its core competency of translating a Halyard config file into the config files for the individual microservices. Halyard will expose a single command that takes as input a Halyard config and outputs to a specified directory the configurations for each microservice, as well as files referenced by these config files.

This command will roughly map onto the current hal config generate command.

API contract

Input

The input to kleat will be a Halyard config file, expressed as YAML. In order to promote backwards compatibility, the format of this config file will change only minimally from the Halyard config.

Notably, the changes that will be made are:

  • A Halyard-generated halconfig contains two top-level fields: deploymentConfigurations (a list of HalConfigs) and currentDeployment, (the name of the deploymentConfiguration to manage). Kleat will accept a file with a single config as input, so any halconfigs with multiple deploymentConfigurations need to be separated into different files. Feedback from users is that having multiple configs in a single file was rarely, if ever, used.
  • Fields where minor changes would greatly simplify kleat and reduce its dependence on microservice-specific details will be changed along with clear upgrade documentation on the changes required. A list of fields found to date can be found here. Note that most users will only have configured a small subset of these fields, so the burden on upgrade should be small.

In addition, there will be some fields that are no longer relevant in kleat; these fields will be documented as being ignored by kleat. Depending on feedback from initial adopters, kleat may emit a non-fatal warning if these fields are set. (An example of such a field is deploymentEnvironment.tolerations, which does not affect the generation of service configurations but only adds fields to the output deployment YAML.)

As the Halyard config is not currently well-documented (with the documentation instead living on the hal command reference), we will add extensive documentation on this config file. In order to ensure the documentation stays up to date, the technical implementation will keep the documentation alongside the code and auto-generate user-facing documentation from this documented code.

Referenced files

In many cases, the Halyard config directly references files that are on disk on the machine running Halyard. For example, the hal config might point to a file containing a service account key that needs to be present in the container running clouddriver.

Halyard has allowed the hal config to reference files anywhere on disk on the machine running Halyard; as part of its config generation, it:

  • copies these files to a staging directory
  • updates all the config files to point to this staging directory
  • mounts all these files in the deployed containers using the path of the staging directory

In order to make the handling of external files (which are generally sensitive) more flexible, kleat will handle cases where the config points to files as follows:

  • The hal config should reference the location of the file as it will be mounted in the container.
  • The default kustomize install pathway will mount a Kubernetes secret into /var/secrets in each container. Users can add any files to this secret in their overlay, and the files will then be mounted under /var/secrets in the pods for each service.
    • Users using this workflow would, for example, reference /var/secrets/my-token.json in their hal config. Then in their overlay, they would add my-token.json to the secret in the base kustomization, which would cause it to be mounted at that path in every container.
  • Users who wish to handle secret deployment out-of-band can do so; they would reference the mounted path of the secret file in their hal config and would be responsible for mounting that secret in all containers (such as with JSON patches in their overlay).

It is worth noting that this approach to handling files referenced in the config is one area where we are most interested in feedback from early adopters, and are definitely open to improvements in this workflow if users find it cumbersome.

Output

The output of kleat will be a directory containing the service YAML of each microservice. As a baseline, hal config generate currently outputs this data to a staging directory and we will use the same format for the output from kleat.

Install Pathways

With kleat, there will be a number of install pathways available to users.

Operator

The operator being built by Armory will replace its dependency on the existing Halyard with kleat. As the operator already abstracts away the parts of Halyard that are being removed, this change should be transparent to the end user.

Kustomize

We’ll provide a Kustomization that contains the necessary Kubernetes YAML for deploying Spinnaker. In order to simplify the configuration in users' overlays, this base kustomization will create empty Secrets for the config and referenced files and will mount them in the appropriate places in the containers. Users will then just need to add files to these Secrets in their overlay.

As a way to quickly get started, we'll provide a skeleton repo that users can clone and add their config to.

An overview of how to deploy one service this way is provided here, but the quick overview is that users will need to:

  • Run kleat on their hal config, to generate their service configs.
  • Add those service configs to the relevant config maps in their kustomization.yaml. (This is already done in the skeleton repo.)
  • Add any referenced files to the spinnaker-secrets secret in their kustomization.yaml
  • For some users, this will be all and they run kustomize build and deploy the result.
  • Other users may want to:
    • Add some -local.yml config files
    • Configure a custom redis endpoint
    • Add custom patches to the deployed services

In terms of customizing the deployment, some users may want to apply JSON patches to the base config in their overlay, and others may want to fork the base config and directly modify the YAML. At this point we don't have a strong opinion about which path users should take and intend to support both.

Users can select a version of Spinnaker to deploy by supplying container tag overrides in their kustomization.yaml file. The release process will be updated so that published container images will be tagged with their top-level version (ex: spinnaker-1.20.1). This avoids the need to fetch a BOM and parse it to find the the specific tag for each microservice.

Helm

The solution here is less clear, as there is not a great way to pass config files to Helm; to have a native Helm installation, it would be necessary to reproduce the entire Halyard config in the values file, and re-implement kleat in Helm’s templating language. A better solution would be to have Helm install the operator, which is similar to how the chart currently just installs Halyard but should provide a more Kubernetes-native experience.

The initial implementation is focusing on the Kustomize install path, and there are no immediate plans to add a Helm install pathway.

Manual

Users with enough Kubernetes experience, or with enough special use cases may want to manually write the YAML for their Spinnaker deployment. In this case, they’d use kleat to generate the required service configuration files, and would then feed these into their process for generating the YAML required to deploy Spinnaker.

Non-Kubernetes

Users who are not using Kubernetes will still be able to use kleat to generate their config files and stage any dependent files. As is the case for Kubernetes, Halyard will no longer handle actually deploying the services to VMs; users will be responsible for putting the generated configs in the expected location and fetching/starting the services. As Halyard currently only supports deploying all services to the same machine where Halyard is running, it's not clear that this was commonly used for actual production setups; the fact that kleat will have an explicit contract to output the required config files should make it easier to build downstream tooling for deploying to VMs for users that want this functionality.

Technical Overview

Refactor or replace

Given the above discussion about the shortcomings of the current implementation of Halyard, and the fact that we are proposing to only support a small core of the current functionality, we will re-implement this core part instead of refactoring Halyard.

This has the advantage of allowing the existing Halyard to be maintained while the new kleat is being implemented and adopted by end users; it also insulates the existing Halyard from quick iteration on kleat. One disadvantage of this approach is that there will be a period of time where we need to maintain both the old and new Halyard.

CLI vs. Daemon

Halyard is currently implemented as a CLI and a daemon, greatly adding to its complexity. This decision was made to allow support for clients other than the CLI, but to date no such implementations have been written and none are planned. The new tool will replace this with a CLI only, with no background daemon process.

Language

kleat will be written in Go, which has the following advantages:

  • The primary initial consumer of kleat will be the Armory Operator, which is also written in Go and will be able to consume parts of kleat as a library
  • Operators deploying to Kubernetes are usually much more familiar with Go than with Java, so this will likely lead to an easier path to contribution from the community
  • Go is well-suited for writing simple command-line tools

Drawbacks

This change will require users to change their workflow for deploying Spinnaker in order to adopt kleat. While the format of the Halyard config itself will not change, users will need to change the way they actually deploy Spinnaker from running hal deploy apply to using one of the above-described install pathways.

Prior Art and Alternatives

One alternative to the current approach of writing a new tool to replace Halyard would be to refactor the existing Halyard to accomplish the same goals. That being said, given the assessment above that the majority of Halyard's functionality is either low-value or exists in other popular tools, the amount of code reuse that would be possible by an in-place refactor is minimal. An in-place refactor would also add the risk of breaking existing users during the implementation of this RFC.

Overall, one of the primary motivations of this RFC is to remove functionality from Halyard that duplicates existing tools with larger market share, and instead build a tool that integrates well with these existing tools. This has the benefit of allowing users to install Spinnaker using tools that are familiar to them, and removes the maintenance burden of Halyard's custom implementation of duplicative tools.

Known Unknowns

At this point, there are still a few details that are unknown and will be clarified during the implementation and testing phases:

  • The exact format of the output from the CLI tool. It will need to output the service configs as well as (possibly) some metadata about the Spinnaker deployment (ex: the versions of containers to pull) but the exact format will be determined in concert with early consumers.
  • The exact format of the Helm chart and Kustomize kustomization that will be provided to support installation to Spinnaker remains unspecified.

Security, Privacy, and Compliance

The Halyard configuration often contains secrets that are eventually included in the microservice configuration files (ex: tokens/passwords for communicating with external services) as discussed in the above section on secret management.

By removing the ability for Halyard to decrypt these secrets and forcing the the services themselves to handle decryption, we are ensuring end-to-end encryption and eliminating one potential vulnerability point.

Operations

Migration to kleat will involve some one-time work to update any scripts or procedures that organizations have developed to deploy Spinnaker. In particular, some configuration that existed in the Halyard configuration will now be moved to the Helm or Kustomize layer, and will require users to update their configuration accordingly.

While this will be a one-time migration effort, it will move users to tools that have wide adoption in the Kubernetes community and which are likely familiar to operators. This should simplify ongoing maintenance and updates to their Spinnaker deployment by reducing the amount that users need to learn about Spinnaker-specific tooling and instead leveraging their knowledge of more general Kubernetes tools.

Risks

The primary risk here is that users do not want to migrate to kleat, either because there is an important user story that it does not support, or because it does not provide enough of an improvement as incentive for the one-time migration costs. As the existing Halyard will continue to be supported during the transition, the primary risk here is wasted effort if kleat does not get enough adoption to warrant continued maintenance. A more likely outcome is that feedback from initial testers results in updates to this plan to better support their use cases, which might delay the full GA availability of kleat.

Future Possibilities

Once Kubernetes-specific configuration for a Spinnaker deployment has been moved out of Halyard and into Kubernetes-specific tools such as Helm and Kustomize, there is a lot of value that could be derived from adding features to these Helm charts and Kustomize kustomizations. For example, one could imagine users sharing (and/or contributing upstream) useful HA or fault-tolerant deployments of Spinnaker. Given that these configurations would be in tools/languages familiar to operators deploying to Kubernetes instead of in a Spinnaker-specific tool, it is likely that there would be more community participation than there currently is in Halyard.