2022-01-28: Alertmanager Notifications Failing

Incident DRI

@alejandro

Current Status

The Alert Manager Notifications were failing. Only internal customers were impacted. We have mitigated the issue by reverting two MRs that could have caused this incident:

• Revert "Merge branch 'pguinoiseau/thanos-rules-staging-ref' into 'master'"
• Revert "Merge branch 'pguinoiseau/thanos-staging-ref' into 'master'"

We are continuing the investigation.

Summary for CMOC notice / Exec summary:

We reconfigured alertmanager recently and we are investigating whether or not this change has caused the alerts manager notifications to fail.

1. Customer Impact: ServiceAlertManager
2. Customer Impact Duration: 45 minutes
3. Current state: IncidentActive
4. Root cause: RootCauseConfig-Change

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Timeline

Recent Events (available internally only):

• Deployments
• Feature Flag Changes
• Infrastructure Configurations
• GCP Events (e.g. host failure)

All times UTC.

2022-01-28

• 11:17 - alejandro declares incident in Slack.
• 11:19 - Alejandro observes errors when trying to query this metric on thanos
• 11:21 - Alejandro suspects the error could be due to a recent alert manager configuration change
• 11:26 - Alejandro notices the error message directly references a staging-ref cluster
• 11:35 - Alejandro creates an MR to Revert "Merge branch 'pguinoiseau/thanos-rules-staging-ref' into 'master'"
• 11:52 - Pierre suggest that we revert this MR to disconnect it completely from Thanos until we can investigate the issue next week
• 11:53 - gitlab-com/runbooks!4283 (merged) merged
• 11:55 - Alejandro creates an MR to Revert "Merge branch 'pguinoiseau/thanos-staging-ref' into 'master'"
• 12:01 - Tanka deployment revert merged gitlab-com/gl-infra/k8s-workloads/tanka-deployments!304 (merged)
• 12:05 - Pierre observes the GitLab metrics took a dip and suggests there might have been an issue with the GKE cluster

Takeaways

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Corrective Actions

Corrective actions should be put here as soon as an incident is mitigated, ensure that all corrective actions mentioned in the notes below are included.

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Incident Review

• Ensure that the exec summary is completed at the top of the incident issue, the timeline is updated and relevant graphs are included in the summary
• If there are any corrective action items mentioned in the notes on the incident, ensure they are listed in the "Corrective Action" section
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Customer Impact

1. Who was impacted by this incident? (i.e. external customers, internal customers)
   1. Internal customer: Infrastructure
2. What was the customer experience during the incident? (i.e. preventing them from doing X, incorrect display of Y, ...)
   1. Missing alert notifications
3. How many customers were affected?
   1. ...
4. If a precise customer impact number is unknown, what is the estimated impact (number and ratio of failed requests, amount of traffic drop, ...)?
   1. ...

What were the root causes?

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Incident Response Analysis

1. How was the incident detected?
   1. ...
2. How could detection time be improved?
   1. ...
3. How was the root cause diagnosed?
   1. ...
4. How could time to diagnosis be improved?
   1. ...
5. How did we reach the point where we knew how to mitigate the impact?
   1. ...
6. How could time to mitigation be improved?
   1. ...
7. What went well?
   1. ...

Post Incident Analysis

1. Did we have other events in the past with the same root cause?
   1. ...
2. Do we have existing backlog items that would've prevented or greatly reduced the impact of this incident?
   1. ...
3. Was this incident triggered by a change (deployment of code or change to infrastructure)? If yes, link the issue.
   1. ...

What went well?

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Guidelines

• Blameless RCA Guideline

Resources

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