fix(backend): stop heartbeat status updates for ScheduledWorkflows. Fixes #8757

[demarna1]

Goal

Fix high ETCD usage of Kubeflow ScheduledWorkflows. Closes https://github.com/kubeflow/pipelines/issues/8757

Context

Every time the ScheduledWorkflow controller syncs a SWF resource, it updates the Last Heartbeat Time and Last Transition Time to the current time in the status block.

Status:
  Conditions:
    Last Heartbeat Time:   2024-11-07T11:16:33Z
    Last Transition Time:  2024-11-07T11:16:33Z
    Message:               The schedule is disabled.
    Reason:                Disabled
    Status:                True
    Type:                  Disabled

These heartbeat updates result in an infinite reconciliation loop:

• SWF is added to controller work queue.
• Controller processes the SWF and updates the status' LastProbeTime and LastTransitionTime to current time.
• Object is re-written to ETCD and the resourceVersion is updated.
• Shared informer detects that the resourceVersion has changed.
• Controller event handler re-adds the SWF to the work queue.
• This reconciliation loop occurs every 10 seconds for every SWF resource on the cluster. The reason it's 10s and not 1s is because the controller has a default queue backoff of 10s, so events are always queued for a minimum of 10s.

Description of the fix

The LastProbeTime and LastTransitionTime fields in the ScheduledWorkflow Status are unused by Kubeflow so it is safe to set these fields to 0 for now in order to fix the ETCD performance issues (which for us has resulted in ETCD outages). By keeping these fields constant, the object can be reconciled and the writes to ETCD stop. The schedules continue to function as before. Verbose logging is significantly reduced in several pods. A long-term plan for these fields should be determined (it may be best to remove them from the CRD entirely).

ETCD performance before & after

I measured ETCD bytes written for all resources on our cluster over a 10 minute time span. Once this fix was instituted, we saw a dramatic decrease in ETCD usage (see chart below).

The chart roughly agrees with the back-of-the-napkin math:

• The average size of our SWF objects is 270kb.
• Controller re-writes the object every 10 seconds (6x/min).
• Bytes written to ETCD per minute = 270kb x 6/min = 1.6MB/minute per SWF.
• Our cluster had 54 SWFs at the time of the analysis.
• ETCD write throughput is 54*1.6mb/min = 86mb/min = 430MB every 5 min.

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[google-oss-prow[bot]]

Hi @demarna1. Thanks for your PR.

I'm waiting for a kubeflow member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[droctothorpe]

/ok-to-test

[hbelmiro]

Also @demarna1, can you please link the PR to the issue?

[demarna1]

@hbelmiro linked the PR to the issue.

The LastProbeTime and LastTransitionTime fields in the ScheduledWorkflow Status are unused by Kubeflow so it is safe to set these fields to 0 (...) A long-term plan for these fields should be determined (it may be best to remove them from the CRD entirely).

Any reason for not removing them right now?

My first priority is addressing the ETCD performance issue and I didn't want a CRD change to delay it. But I see no reason we can't remove them and I'd be happy to do that in a follow-on PR!

[droctothorpe]

@hbelmiro do you happen to know why the ok-to-test label is no longer triggering the workflows / CI? It used to be sufficient as recently as a few weeks ago.

[hbelmiro]

@hbelmiro do you happen to know why the ok-to-test label is no longer triggering the workflows / CI? It used to be sufficient as recently as a few weeks ago.

@droctothorpe I don't know :( It seems like something has changed in the repo's permissions. The following used to work for first-time contributors.

/rerun-all /ok-to-test

[droctothorpe]

Thanks, @hbelmiro! @HumairAK @zijianjoy do you happen to know if this change was intentional? It's out of sync with this documentation about membership privileges.

[droctothorpe]

Bump.