The unregister timeout of 1 minute (no matter how long it is) can negatively impact availability of static runner constantly running workflow jobs, and ephemeral runner that runs a long-running job.
We deal with that by completely removing the unregistaration timeout, so that regarldess of the type of runner(static or ephemeral) it waits forever until it successfully to get unregistered before being terminated.
Since #1127 and #1167, we had been retrying `RemoveRunner` API call on each graceful runner stop attempt when the runner was still busy.
There was no reliable way to throttle the retry attempts. The combination of these resulted in ARC spamming RemoveRunner calls(one call per reconciliation loop but the loop runs quite often due to how the controller works) when it failed once due to that the runner is in the middle of running a workflow job.
This fixes that, by adding a few short-circuit conditions that would work for ephemeral runners. An ephemeral runner can unregister itself on completion so in most of cases ARC can just wait for the runner to stop if it's already running a job. As a RemoveRunner response of status 422 implies that the runner is running a job, we can use that as a trigger to start the runner stop waiter.
The end result is that 422 errors will be observed at most once per the whole graceful termination process of an ephemeral runner pod. RemoveRunner API calls are never retried for ephemeral runners. ARC consumes less GitHub API rate limit budget and logs are much cleaner than before.
Ref https://github.com/actions-runner-controller/actions-runner-controller/pull/1167#issuecomment-1064213271
While testing #1179, I discovered that ARC sometimes stop resyncing RunnerReplicaSet when the desired replicas is greater than the actual number of runner pods.
This seems to happen when ARC missed receiving a workflow_job completion event but it has no way to decide if it is either (1) something went wrong on ARC or (2) a loadbalancer in the middle or GitHub or anything not ARC went wrong. It needs a standard to decide it, or if it's not impossible, how to deal with it.
In this change, I added a hard-coded 10 minutes timeout(can be made customizable later) to prevent runner pod recreation.
Now, a RunnerReplicaSet/RunnerSet to restart runner pod recreation 10 minutes after the last scale-up. If the workflow completion event arrived after the timeout, it will decrease the desired replicas number that results in the removal of a runner pod. The removed runner pod might be deleted without ever being used, but I think that's better than leaving the desired replicas and the actual number of replicas diverged forever.
Yusuke Kuoka