2020-12-25: Praefect proxy latency apdex intermittently exceeding SLO

Summary

Praefect is intermittently alerting that its mean response time latency is exceeding SLO.

This may be a side-effect of our alerting threshold being too sensitive for the shift in traffic pattern during the holidays, as has been the case with a couple other SLO metrics.

Timeline

All times UTC.

2020-12-25

• 23:40 - 1st PagerDuty alert - https://gitlab.pagerduty.com/incidents/PMS4YYF
• 23:40 - 1st PagerDuty alert cleared
• 23:55 - 2nd PagerDuty alert - https://gitlab.pagerduty.com/incidents/PY7YOC2
• 23:58 - msmiley declares incident in Slack.
• 23:59 - 2nd PagerDuty alert cleared

2020-12-29

• 07:03 - another PagerDuty alert
• 07:05 - PagerDuty alert clears

Corrective Actions

• https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/12219 - Refine Praefect's apdex definition, and make it easy to find the relevant gRPC calls in Kibana

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Incident Review

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Summary

1. Service(s) affected:
2. Team attribution:
3. Time to detection:
4. Minutes downtime or degradation:

Metrics

Customer Impact

1. Who was impacted by this incident? (i.e. external customers, internal customers)
   1. ...
2. What was the customer experience during the incident? (i.e. preventing them from doing X, incorrect display of Y, ...)
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3. How many customers were affected?
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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?

"5 Whys"

Incident Response Analysis

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

Lessons Learned

Guidelines

• Blameless RCA Guideline

Resources

1. If the Situation Zoom room was utilised, recording will be automatically uploaded to Incident room Google Drive folder (private)

Incident Review Stakeholders