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[CR][GSTG] Migrate cache workload to redis-cluster-cache

Production Change

Change Summary

This closes the provisioning issue and migrates cache workload on gstg.

The secondary objectives of this migration on gstg are:

  • Rehearsing the cache-warmup with dual-write and validator script's extra migration
  • Practice a rollback (diverting read traffic back to redis-cache)

See scalability#2074

Feature flag rollout issue: gitlab-org/gitlab#415029 (closed)

Change Details

  1. Services Impacted - ServiceRedisCache ServiceRedisClusterCache
  2. Change Technician - @schin1
  3. Change Reviewer - @stejacks-gitlab
  4. Time tracking - ~72 hours (3 days)
  5. Downtime Component - NA

Detailed steps for the change

Change Steps - steps to take to execute the change

Estimated Time to Complete (48hr)

Complete provisioning step

Cache warming

  • To start dual-write: Enable the use_primary_and_secondary_stores_for_cache feature flag for gstg
    • /chatops run feature set use_primary_and_secondary_stores_for_cache true --staging
  • Wait for 24 hours
  • Run validator script https://gitlab.com/gitlab-com/runbooks/-/blob/master/scripts/redis_diff.rb from a console VM with redis-cache as the source while redis-cluster-cache as the destination

Cutover reads

  • To cutover: Enable use_primary_store_as_default_for_cache to cut over read traffic.
    • /chatops run feature set use_primary_store_as_default_for_cache true --staging
Click to show removed component

Rollback reads

Cutover read and write

  • Disable use_primary_and_secondary_stores_for_cache to halt double-write.
  • Set label changecomplete /label ~change::complete

Rollback

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

Estimated Time to Complete (mins) - Estimated Time to Complete in Minutes

Monitoring

Key metrics to observe

Change Reviewer checklist

C4 C3 C2 C1:

  • Check if the following applies:
    • 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:

  • Check if the following applies:
    • 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.
    • The labels blocks deployments and/or blocks feature-flags are applied as necessary

Change Technician checklist

  • Check if all items below are complete:
    • The change plan is technically accurate.
    • This Change Issue is linked to the appropriate Issue and/or Epic
    • 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.
    • The change execution window respects the Production Change Lock periods.
    • For C1 and C2 change issues, the change event is added to the GitLab Production calendar.
    • For C1 and C2 change issues, the 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.)
    • For C1 and C2 change issues, the SRE on-call provided approval with the eoc_approved label on the issue.
    • For C1 and C2 change issues, the Infrastructure Manager provided approval with the manager_approved label on the issue.
    • 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 that are severity1 or severity2
    • If the change involves doing maintenance on a database host, an appropriate silence targeting the host(s) should be added for the duration of the change.
Edited by Sylvester Chin