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Functionally shard redis-db-load-balancing from redis-persistent in production.

Production Change

Change Summary

Using feature flags, we will first dual write all redis-db-load-balancing keys to both redis-db-load-balancing and then redis-persistent, and then we will transition to only using redis-db-load-balancing.

Change Details

  1. Services Impacted - ServiceRedis
  2. Change Technician - @alejandro
  3. Change Reviewer - @stejacks-gitlab
  4. Time tracking - 90

Detailed steps for the change

Pre-change Steps

Estimated Time to Complete (mins) - 30 minutes

  • Update chef-repo vault with new password and key:
$ bin/gkms-vault-edit gitlab-omnibus-secrets gprd

"gitlab-rails": {
...
  "redis_yml_override": {
    "db_load_balancing": {
      "url": "redis://<IAMAPASSWORD>@gprd-redis-db-load-balancing"
    }
  },
...

Change Steps - steps to take to execute the change

Estimated Time to Complete (mins) - 30 minutes

  • Set label changein-progress /label ~change::in-progress
  • Start dual writes: /chatops run feature set use_primary_and_secondary_stores_for_db_load_balancing true --ignore-feature-flag-consistency-check
  • Monitor for fallback queries and hit rate.. We don't expect this to flatten out (see this discussion), but check it isn't growing unbound and that the rate is low (we're expecting ~1e-1 or less)
  • Wait 10 minutes to allow for failback if required.
  • Start primary write: /chatops run feature set use_primary_store_as_default_for_db_load_balancing true
  • Stop dual write: /chatops run feature set use_primary_and_secondary_stores_for_db_load_balancing false
  • 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) - 30 minutes.

  • Turn all feature flags to false:
/chatops run feature set use_primary_and_secondary_stores_for_db_load_balancing false
/chatops run feature set use_primary_store_as_default_for_db_load_balancing false

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 Alejandro Rodríguez