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Incidents/2021-11-25 eventgate-main outage

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document status: in-review

Summary and Metadata

Incident ID 2021-11-25 eventgate-main outage UTC Start Timestamp: 2021-11-25 07:32
Incident Task https://phabricator.wikimedia.org/T299970 UTC End Timestamp 2021-11-25 07:35
People Paged 0 Responder Count 1
Coordinator(s) No Coordinator needed Relevant Metrics / SLO(s) affected
  • 25k MediaWiki backend errors
  • 1k web & API requests resulted in a 500
  • Event intake dropped to 0 (from 3k) for the duration

No SLO defined, no error budget consumed

Summary: For about 3 minutes (from 7:32 to 7:35 UTC), eventgate-main was unavailable. This resulted in 25,000 unrecoverable MediaWiki backend errors due to inability to queue new jobs. About 1,000 user-facing web requests and API requests failed with an HTTP 500 error. Event intake processing rate measured by eventgate briefly dropped from ~3000/second to 0/second during the outage.

During the helm3 migration of eqiad Kubernetes cluster the service eventgate-main experience an outage. The service was not available between 7:32 and 7:35 UTC.

For the helm3 migration the service had to be removed and re-deployed to the cluster. Most Kubernetes services were explicitly pooled in codfw-only during the re-deployments. eventgate-main was also falsely assumed to be served by Codfw but was still pooled in Eqiad. So during the time of removing and re-creating the pods, no traffic could be served for this service.

The commands used to migrate and re-deploy codfw (see T251305#7492328) were adapted and re-used for eqiad (see T251305#7526591). Due to a small difference in what Kubernetes services are pooled as active-active and what are active-passive, eventgate-main was missing in the depooling command (as is it not pooled in codfw currently).

Impact: For about 3 minutes (from 7:32 to 7:35 UTC), eventgate-main was unavailable. This resulted in 25,000 unrecoverable MediaWiki backend errors due to inability to queue new jobs. About 1,000 user-facing web requests and API requests failed with an HTTP 500 error. Event intake processing rate measured by eventgate briefly dropped from ~3000/second to 0/second during the outage.

Documentation:

Scorecard

Incident Engagement™  ScoreCard Score
People Were the people responding to this incident sufficiently different than the previous N incidents? (0/5pt) 5
Were the people who responded prepared enough to respond effectively (0/5pt) 4
Did fewer than 5 people get paged (0/5pt)? 5
Were pages routed to the correct sub-team(s)? N/A
Were pages routed to online (working hours) engineers (0/5pt)? (score 0 if people were paged after-hours) N/A
Process Was the incident status section actively updated during the incident? (0/1pt) N/A
If this was a major outage noticed by the community, was the public status page updated? If the issue was internal, was the rest of the organization updated with relevant incident statuses? (0/1pt) N/A
Is there a phabricator task for the incident? (0/1pt) 0
Are the documented action items assigned?  (0/1pt) 1
Is this a repeat of an earlier incident (-1 per prev occurrence) 0
Is there an open task that would prevent this incident / make mitigation easier if implemented? (0/-1p per task) -1
Tooling Did the people responding have trouble communicating effectively during the incident due to the existing or lack of tooling? (0/5pt) N/A
Did existing monitoring notify the initial responders? (1pt) N/A
Were all engineering tools required available and in service? (0/5pt) 5
Was there a runbook for all known issues present? (0/5pt) 0
Total Score 19

Actionables