2023-01-31: Functionally shard redis-repository-cache from redis-cache in production.
Production Change
Change Summary
Using feature flags, we will first dual write all redis-repository-cache keys to both redis-repository-cache and then redis-cache, and then we will transition to only using redis-cache. The process will take approximately 8 hours (due to TTLs) and will be done during the quiestest period possible, beginning at approximately 2100 UTC (pre-change steps) and completed by 0700 UTC.
scalability#2054 (closed) is the scalability issue.
gitlab-org/gitlab#388080 (closed) is the issue for the feature flags in question.
Change Details
- Services Impacted - ServiceRedis
- Change Technician - @stejacks-gitlab and @reprazent
- Change Reviewer - @msmiley
- Time tracking - 24h
Detailed steps for the change
Pre-change Steps
Estimated Time to Complete (mins) - 60 minutes
-
Update chef-repo vault with new password and key:
stejacks@atlas~/projects/gitlab-com/gl-infra/chef-repo (master) $ EDITOR=vim bin/gkms-vault-edit gitlab-omnibus-secrets gprd
"gitlab-rails": {
...
"redis_repository_cache_instance": "redis://<IAMAPASSWORD>@gprd-redis-repository-cache",
...
-
Merge chef-repo MR https://gitlab.com/gitlab-com/gl-infra/chef-repo/-/merge_requests/2791 -
Merge k8s-workloads MR gitlab-com/gl-infra/k8s-workloads/gitlab-com!2535 (merged)
Change Steps - steps to take to execute the change
Estimated Time to Complete (mins) - 1440 minutes
-
Set label changein-progress /label ~change::in-progress
-
Start dual writes: /chatops run feature set use_primary_and_secondary_stores_for_repository_cache true
-
Monitor for fallback queries and hit rate, wait for fallback queries to flatten out. This should take approximately 8 hours. -
Wait 24 hours to allow for failback if required. -
Start primary write: /chatops run feature set use_primary_store_as_default_for_repository_cache true
-
Stop dual write: /chatops run feature set use_primary_and_secondary_stores_for_repository_cache false
-
Take RDB dump on one redis-cache secondary and one redis-repository-cache secondary shortly after turning off the feature flags.
$ sudo gitlab-redis-cli bgsave
# Monitor the file on disk, once it stops increasing in size, it's ready to be used!
$ sudo ls -lta /var/opt/gitlab/redis/dump.rdb
# Once the file is ready, move it to a safe-er location, for example
$ sudo mv /var/opt/gitlab/redis/dump.rdb /var/opt/gitlab/redis/dump-8309.rdb
-
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_repository_cache false
/chatops run feature set use_primary_store_as_default_for_repository_cache false
-
Set label changeaborted /label ~change::aborted
Monitoring
Key metrics to observe
-
Metric: All redis metrics for redis-repository-cache and redis-cache.
- Location: Redis-cache: https://dashboards.gitlab.net/d/redis-cache-main/redis-cache-overview?orgId=1 Redis-repository-cache: https://dashboards.gitlab.net/d/redis-repository-cache-main/redis-repository-cache-overview?orgId=1
- What changes to this metric should prompt a rollback: Hitting the 1h SLO outage rate for apdex or error rate for redis-cache or redis-repository-cache.
-
Metric: Redis-fallback-queries and hit rates:
Change Reviewer checklist
-
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.
-
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.