2022-03-15: Increase zip cache expiration for pages

Production Change

Change Summary

GitLab Pages uses some zip files for serving content, which gets cached. The current cache expiration is 120 seconds. We aim to increase the expiration slowly and check how it affects the hit rate. The MR increase zip cache expiration to 300s.

Change Details

1. Services Impacted - ServicePages
2. Change Technician - @vtak
3. Change Reviewer - @skarbek
4. Time tracking - unknown
5. Downtime Component - none

Detailed steps for the change

Pre-Change Steps - steps to be completed before execution of the change

Estimated Time to Complete (mins) - 1

• Set label changein-progress on this issue

Change Steps - steps to take to execute the change

Estimated Time to Complete (mins) - 15

• Merge and apply MR

Post-Change Steps - steps to take to verify the change

Estimated Time to Complete (mins) - 1

• Verify Pages is up by visiting any gitlab page e.g. https://vtak.gitlab.io/gitlab-for-eks/

Rollback

Rollback steps - steps to be taken in the event of a need to rollback this change

Estimated Time to Complete (mins) - 15

• Revert MR

Monitoring

Key metrics to observe

• Metric: Pages Apdex and Service Error Ratio
  • Location: https://dashboards.gitlab.net/d/web-pages-main/web-pages-overview?orgId=1
  • What changes to this metric should prompt a rollback: lower apdex or increased errors
• Metric: Hit Rate for archive operation
  • Location: https://thanos-query.ops.gitlab.net/graph?g0.expr=sum(gitlab_pages_zip_cached_entries%7Benv%3D%22gprd%22%7D)%20by%20(op)&g0.tab=0&g0.stacked=0&g0.range_input=1w&g0.max_source_resolution=0s&g0.deduplicate=1&g0.partial_response=0&g0.store_matches=%5B%5D&g1.expr=sum(rate(gitlab_pages_zip_cache_requests%7Benv%3D%22gprd%22%2Ccache%3D%22hit%22%7D%5B1h%5D))%20by%20(op%20)%20%2F%20sum(rate(gitlab_pages_zip_cache_requests%7Benv%3D%22gprd%22%20%7D%5B1h%5D))%20by%20(op%20)&g1.tab=0&g1.stacked=0&g1.range_input=1w&g1.max_source_resolution=0s&g1.deduplicate=1&g1.partial_response=0&g1.store_matches=%5B%5D:
  • What changes to this metric should prompt a rollback: significant decrease in hit rate

Summary of infrastructure changes

• Does this change introduce new compute instances? No
• Does this change re-size any existing compute instances? No
• Does this change introduce any additional usage of tooling like Elastic Search, CDNs, Cloudflare, etc? No

Change Reviewer checklist

C4 C3 C2 C1:

• The scheduled day and time of execution of the change is appropriate.
• The change plan is technically accurate.
• The change plan includes estimated timing values based on previous testing.
• The change plan includes a viable rollback plan.
• The specified metrics/monitoring dashboards provide sufficient visibility for the change.

C2 C1:

• The complexity of the plan is appropriate for the corresponding risk of the change. (i.e. the plan contains clear details).
• The change plan includes success measures for all steps/milestones during the execution.
• The change adequately minimizes risk within the environment/service.
• The performance implications of executing the change are well-understood and documented.
• The specified metrics/monitoring dashboards provide sufficient visibility for the change. - If not, is it possible (or necessary) to make changes to observability platforms for added visibility?
• The change has a primary and secondary SRE with knowledge of the details available during the change window.

Change Technician checklist

• This issue has a criticality label (e.g. C1, C2, C3, C4) and a change-type label (e.g. changeunscheduled, changescheduled) based on the Change Management Criticalities.
• This issue has the change technician as the assignee.
• Pre-Change, Change, Post-Change, and Rollback steps and have been filled out and reviewed.
• This Change Issue is linked to the appropriate Issue and/or Epic
• Necessary approvals have been completed based on the Change Management Workflow.
• Change has been tested in staging and results noted in a comment on this issue.
• A dry-run has been conducted and results noted in a comment on this issue.
• SRE on-call has been informed prior to change being rolled out. (In #production channel, mention @sre-oncall and this issue and await their acknowledgement.)
• Release managers have been informed (If needed! Cases include DB change) prior to change being rolled out. (In #production channel, mention @release-managers and this issue and await their acknowledgment.)
• There are currently no active incidents.