2022-07-27: HTTP 502 from API requests with pagination on https://gitlab.com/api/v4/projects

Incident Roles

The DRI for this incident is the incident issue assignee, see roles and responsibilities.

Roles when the incident was declared:

• Incident Manager (IMOC): @splattael, @mkaeppler, @m_gill
• Engineer on-call (EOC): @gsgl

Current Status

At around 2022-07-26 1730 UTC we began seeing an increase in 502 logged errors in CloudFlare. This coordinated with a deploy but errors were not seen in the application. The errors were related to the CSP headers being too large resulting in headers above 4k (Nginx's default proxy-buffer-size setting is 4k). We have resolved this incident by reducing CSP headers and increasing the proxy-buffer-size setting to 8k.

Summary for CMOC notice / Exec summary:

1. Customer Impact: Some requests to /api/v4/projects are timing out.
2. Service Impact: ServiceAPI
3. Impact Duration: July 26 - 17:30 UTC - July 27 - 14:13 UTC.
4. Root cause: Rails upgrade

Timeline

Recent Events (available internally only):

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

All times UTC.

2022-07-26

• 17:30 - increase in 502 logged errors in CF.

2022-07-27

• 05:46 - @pguinoiseau declares incident in Slack.
• 10:49 - gitlab-com/gl-infra/k8s-workloads/gitlab-com!1989 (merged) merged.
• 11:25 - MR applied
• 11:30 - 502's drop considerably
• 12:46 - receiving a report of some 502's for specific paths
• 13:35 - gitlab-com/gl-infra/k8s-workloads/gitlab-com!1990 (merged) merged
• 14:13 - Incident has been confirmed as resolved

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• Corrective action
• Investigation followup
• Confidential / Support contact
• QA investigation
• Infradev

Takeaways

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Corrective Actions

• Increase the proxy_buffer_size (done)
• Prevent generating links with all of the params present - For example the Link header can grow quite large, which happens for all endpoints but Project and Group/Project endpoints has a lot of possible params.
  • <https://gitlab.com/api/v4/projects?imported=false&membership=false&order_by=created_at&owned=false&page=1&per_page=20&repository_checksum_failed=false&simple=false&sort=desc&starred=false&statistics=false&wiki_checksum_failed=false&with_custom_attributes=false&with_issues_enabled=false&with_merge_requests_enabled=false>; rel="prev", <https://gitlab.com/api/v4/projects?imported=false&membership=false&order_by=created_at&owned=false&page=3&per_page=20&repository_checksum_failed=false…
• Use a different CSP for API endpoints (in progress)
• Create tests/validation for CSP headers across environments

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Incident Review

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Customer Impact

1. Who was impacted by this incident? (i.e. external customers, internal customers)
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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, ...)?
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What were the root causes?

• ...

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

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Resources

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