2022-02-08: Websocket service experiencing elevated error rates

Incident DRI

@igorwwwwwwwwwwwwwwwwwwww

Current Status

We recently completed the migration of session data to the new Redis. This resulted in the node using around only 10% of the core Redis Data Storage. Consequently, the decision was made to resize Redis Persistent.

One of the steps during the migration was to perform a Redis Failover. After the failover, the Websocket service had elevated error rates for ~10 minutes.

We have fully recovered and there was no impact to the customers.

Summary for CMOC notice / Exec summary:

1. Customer Impact: There was no customer impact
2. Service Impact: ServiceWebsockets
3. Impact Duration: ~10 minutes
4. Root cause: RootCauseDatabase-Failover

Timeline

Recent Events (available internally only):

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

All times UTC.

2022-02-08

• 10:47 - ActionCable connections drop
• 10:54 - @igorwwwwwwwwwwwwwwwwwwww declares incident in Slack.
• 10:58 - Redis Failover completes
• 11:00 - Incident is mitigated
• 11:42 - Incident is Resolved

Takeaways

• ...

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.

• gitlab-org/gitlab#352250 (closed)

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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
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Customer Impact

1. Who was impacted by this incident? (i.e. external customers, internal customers)
   1. There was no customer impact.
2. What was the customer experience during the incident? (i.e. preventing them from doing X, incorrect display of Y, ...)
   1. N/A
3. How many customers were affected?
   1. N/A
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. N/A

What were the root causes?

• Performing a Redis Failover

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?

• ...

Guidelines

• Blameless RCA Guideline

Resources

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