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2021-12-20: 5 Elasticsearch shards unavailable

Current Status

There is no impact on users of Gitlab.com resulting from this incident.

A script was run to change routing allocation settings for ALL data warm indices and made all indices in warm phase have a _tier_preference of data_warm. Shards are reallocating again and we see the cluster recovering but note that we are not yet fully in clear. Details

We noticed that Elasticsearch shard nodes were failing and suspect the shards are not being moved because of a switch from node attributes and attribute-based allocation filters to using data tiers. We are trying to manually reallocate the shards

More information will be added as we investigate the issue.

Timeline

Recent Events (available internally only):

All times UTC.

2021-12-20

2021-12-21

  • 00:30 - @john-mason corrects warm allocation rules set on indices in hot phase but not under active write alias.
  • 01:30 - @john-mason observed that the cluster health returned to green.

2021-12-23

  • 11:00 - @mwasilewski-gitlab has marked this incident as active again Some shards nodes are failing and they are not being moved again. Yesterday he applied the fix to some of the indices. The shards that are failing today do not have the fix applied.
  • 11:17 - @mwasilewski-gitlab observes that the changes made yesterday worked and he begins applyig the same payload

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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Note: In some cases we need to redact information from public view. We only do this in a limited number of documented cases. This might include the summary, timeline or any other bits of information, laid out in out handbook page. Any of this confidential data will be in a linked issue, only visible internally. By default, all information we can share, will be public, in accordance to our transparency value.


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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
  • Fill out relevant sections below or link to the meeting review notes that cover these topics

Customer Impact

  1. Who was impacted by this incident? (i.e. external customers, internal customers)
    1. Gitlab employees
  2. What was the customer experience during the incident? (i.e. preventing them from doing X, incorrect display of Y, ...)
    1. Unable to view production logs
  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, ...)?
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What were the root causes?

  • Change in Elasticsearch routing rules introduced by an upgrade of the cluster

Incident Response Analysis

  1. How was the incident detected?
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  2. How could detection time be improved?
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  3. How was the root cause diagnosed?
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  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?
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  2. Do we have existing backlog items that would've prevented or greatly reduced the impact of this incident?
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  3. Was this incident triggered by a change (deployment of code or change to infrastructure)? If yes, link the issue.
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What went well?

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Guidelines

Resources

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