2023-03-21: Divert redis-ratelimiting traffic to redis-cluster-ratelimiting

Production Change

Change Summary

Using feature flags, we will cutover Redis traffic for rate-limiting related commands from redis-ratelimiting service to redis-cluster-ratelimiting service. This cutover process takes approximately 1 minute since that is the TTL for the Rails app in-memory cache. This change should be done during the quieter periods (2300-0500 UTC window) to minimise any possible user impacts.

redis-cluster-ratelimiting gprd setup is summarised here - scalability#2256

Related scalability issue: scalability#2072

Feature-flag issue: gitlab-org/gitlab#385681 (closed)

Change Details

1. Services Impacted - ServiceRedisClusterRateLimiting ServiceRedisRateLimiting
2. Change Technician - @msmiley
3. Change Reviewer - @igorwwwwwwwwwwwwwwwwwwww
4. Time tracking - 30m
5. Downtime Component - NA

Detailed steps for the change

Change Steps - steps to take to execute the change

Estimated Time to Complete (mins) - 30m

• Set label changein-progress /label ~change::in-progress
• Create a silence in AlertManager for the cause-based alert for redis-ratelimiting db getting no client traffic:

  alert_class=traffic_cessation
  alert_type=cause
  type=redis-ratelimiting
  alertname=~RedisRatelimitingServiceRailsRedisClientTraffic(Cessation|Absent)

• Run cutover chatops command for just 1% of traffic:

/chatops run feature set use_primary_store_as_default_for_rate_limiting 1 --random

• Verify the plumbing works. Confirm the redis-cluster-ratelimiting dashboard starts showing non-zero rates for the normal workload's expected redis command types (DEL, GET, INCR, etc.).
• Fully enable using redis cluster for all ratelimiting traffic:

/chatops run feature set use_primary_store_as_default_for_rate_limiting true

• 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) - 30m

• Run chatops command

/chatops run feature set use_primary_store_as_default_for_rate_limiting false

• Set label changeaborted /label ~change::aborted

Monitoring

Key metrics to observe

• Metric: All Redis metrics for redis-ratelimiting

  • Location: https://dashboards.gitlab.net/d/redis-ratelimiting-main/redis-ratelimiting-overview?orgId=1
  • What changes to this metric should prompt a rollback: NA. Traffic should fall for this dashboard.

• Metric: All Redis metrics for redis-cluster-ratelimiting

  • Location: https://dashboards.gitlab.net/d/redis-cluster-ratelimiting-main/redis-cluster-ratelimiting-overview?orgId=1
  • What changes to this metric should prompt a rollback: High (Hitting the 1h SLO outage rate) "Service Error Ratio" or SLIs (cluster_redirections, rails_redis_client errors)

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.