Nikola JokicandCopilot App
c441394218
Status.FinishedRunnerCleanupPatchID was only ever set, never cleared, so a marker recorded under one listener incarnation outlived the patch-ID sequence it described. Applying a new actionable revision deletes the idle and pending runners so they are rebuilt from the new spec, and it restarts the listener. A restarted listener numbers its patches from 0 upwards and counts through every integer, so it does not merely risk reusing the leftover value, it passes through it. If that reuse lands on the reconcile that has to refill the pool, the guard suppresses exactly the scale up the revision change asked for. Clearing the marker where the applied revision advances is enough, because the marker only ever means "the gap below Spec.Replicas was made by cleaning up finished runners for this patch ID", and a spec change invalidates that claim outright. That read now bypasses the cache: the patch is a diff against the object that was read, so a cached copy showing 0 while the server held a marker would emit no entry for the field and leave the stale value behind. Clearing the marker also breaks the invariant the cached fast path in scaleUpServicedByFinishedRunnerCleanup rested on. That path was safe only because a marker was never removed, so a cache hit could not be a false positive. Now it can be: a lagging cache can show a marker the server has already cleared, which suppresses the rebuild. The decision is therefore always made against an uncached read. That costs one GET, and only on reconciles that were about to issue creates anyway. One window remains and is documented rather than papered over. A listener that restarts without a spec change keeps the marker and still renumbers from 0, so a collision is still likely. It costs one suppressed reconcile, not an outage: the listener calls back into scaling on every long-poll timeout rather than only on change, and an idle set at its minimum publishes the collapsed patch ID 0, which is never suppressed. This was found while investigating the update-gha-runner-scale-set e2e failure on the tip of the stack. It is a real defect, but it does not explain that failure, whose cause remains open: the suppression here is self-correcting within a long-poll cycle rather than terminal. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Actions Runner Controller (ARC)
About
Actions Runner Controller (ARC) is a Kubernetes operator that orchestrates and scales self-hosted runners for GitHub Actions.
With ARC, you can create runner scale sets that automatically scale based on the number of workflows running in your repository, organization, or enterprise. Because controlled runners can be ephemeral and based on containers, new runner instances can scale up or down rapidly and cleanly. For more information about autoscaling, see "Autoscaling with self-hosted runners."
You can set up ARC on Kubernetes using Helm, then create and run a workflow that uses runner scale sets. For more information about runner scale sets, see "Deploying runner scale sets with Actions Runner Controller."
People
Actions Runner Controller (ARC) is an open-source project currently developed and maintained in collaboration with the GitHub Actions team, external maintainers @mumoshu and @toast-gear, various contributors, and the awesome community.
If you think the project is awesome and is adding value to your business, please consider directly sponsoring community maintainers and individual contributors via GitHub Sponsors.
If you are already the employer of one of the contributors, sponsoring via GitHub Sponsors might not be an option. Just support them by other means!
See the sponsorship dashboard for the former and the current sponsors.
Getting Started
To give ARC a try with just a handful of commands, please refer to the Quickstart guide.
For an overview of ARC, please refer to About ARC.
With the introduction of autoscaling runner scale sets, the existing autoscaling modes are now legacy. The legacy modes have certain use cases and will continue to be maintained by the community only.
For further information on what is supported by GitHub and what's managed by the community, please refer to this announcement discussion.
Documentation
ARC documentation is available on docs.github.com.
Legacy documentation
The following documentation is for the legacy autoscaling modes that continue to be maintained by the community:
- Quickstart guide
- About ARC
- Installing ARC
- Authenticating to the GitHub API
- Deploying ARC runners
- Adding ARC runners to a repository, organization, or enterprise
- Automatically scaling runners
- Using custom volumes
- Using ARC runners in a workflow
- Managing access with runner groups
- Configuring Windows runners
- Using ARC across organizations
- Using entrypoint features
- Deploying alternative runners
- Monitoring and troubleshooting
Contributing
We welcome contributions from the community. For more details on contributing to the project (including requirements), please refer to "Getting Started with Contributing."
Troubleshooting
We are very happy to help you with any issues you have. Please refer to the "Troubleshooting" section for common issues.