[GSTG] Update redis sessions configuration for chef nodes and k8s pods post-migration

Production Change

Change Summary

This is part of the clean up process outlined in gitlab-com/gl-infra/data-access/durability/team#34.

This updates the configuration files for chef nodes and k8s pods to connect to Redis Cluster Sessions hosts for redis-sessions.

Change Details

1. Services Impacted - ServiceRedisSessions ServiceRedisClusterSessions ServiceWeb
2. Change Technician - @marcogreg
3. Change Reviewer - @fshabir
4. Scheduled Date and Time (UTC in format YYYY-MM-DD HH:MM) - 2025-03-12 08:30
5. Time tracking - 60 minutes
6. Downtime Component - none

Set Maintenance Mode in GitLab

If your change involves scheduled maintenance, add a step to set and unset maintenance mode per our runbooks. This will make sure SLA calculations adjust for the maintenance period.

Detailed steps for the change

Change Steps - steps to take to execute the change

Estimated Time to Complete (mins) - 30 minutes

• Set label changein-progress /label ~change::in-progress
• Merge k8s-workloads MR gitlab-com/gl-infra/k8s-workloads/gitlab-com!4167 (merged)
• Set the vault password in ."omnibus-gitlab".gitlab_rb."gitlab-rails".redis_yml_override.sessions.password to match redis cluster sessions password
• Update for chef: https://gitlab.com/gitlab-com/gl-infra/chef-repo/-/merge_requests/5602
• Verify that the configuration is updated using a console as described in https://gitlab.com/gitlab-com/runbooks/-/blob/master/docs/redis/provisioning-redis-cluster.md#2-verification-of-config-in-a-vm
• 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

• Revert depending on the impacted env
• Set label changeaborted /label ~change::aborted

Monitoring

Key metrics to observe

Metric: web apdex

• Location: https://dashboards.gitlab.net/d/web-main/web3a-overview?orgId=1
• What changes to this metric should prompt a rollback: any sharp change in error rates needs to be investigated to ensure configurations are set correctly.

Metric: Redis Cluster Sessions apdex/error rate/RPS

• Location: https://dashboards.gitlab.net/d/redis-cluster-sessions-main/redis-cluster-sessionssessions3a-overview?orgId=1&from=now-6h%2Fm&to=now%2Fm&timezone=utc&var-PROMETHEUS_DS=mimir-gitlab-gstg&var-environment=gstg&var-shard=$__all
• What changes to this metric should prompt a rollback: Drop in apdex / Increase in error rate / anomalies in RPS

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 change window has been agreed with Release Managers in advance of the change. If the change is planned for APAC hours, this issue has an agreed pre-change approval.
  • 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. Mention @gitlab-org/saas-platforms/inframanagers in this issue to request approval and provide visibility to all infrastructure managers.
  • Release managers have been informed prior to any C1, C2, or blocks deployments 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.