2022-07-13: Enable memory watchdog in pre-prod & canaries

Production Change

Change Summary

We are experimenting with a new in-application memory watchdog in gitlab-org/gitlab!91910 (merged).

This component runs in Puma and Sidekiq workers and observes Ruby heap fragmentation. If it trips a given threshold, it issues a callback.

The current callback does nothing, so it's completely safe. All we do is increment Prometheus counters and log these events so that we can learn how sensitive it is. The log volume will be very small since the watchdog only wakes up once a minute and only logs when the threshold is exceeded.

If this approach proves successful in identifying workers that suffer from sustained high memory use due to heap fragmentation, we will follow with a change that reaps these workers automatically.

MR for SaaS config: gitlab-com/gl-infra/k8s-workloads/gitlab-com!1940 (merged)

Change Details

1. Services Impacted - ServiceGitLab Rails ServiceSidekiq
2. Change Technician - @mkaeppler
3. Change Reviewer - @igorwwwwwwwwwwwwwwwwwwww
4. Time tracking - unknown
5. Downtime Component - none

Detailed steps for the change

Rollout plan

See gitlab-org/gitlab#367534 (closed)

Change Steps - steps to take to execute the change

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

• Set label changein-progress /label ~change::in-progress
• Merge MR gitlab-com/gl-infra/k8s-workloads/gitlab-com!1940 (merged)
• 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

• Revert MR gitlab-com/gl-infra/k8s-workloads/gitlab-com!1940 (merged)
• Set label changeaborted /label ~change::aborted

Monitoring

Key metrics to observe

• Metric: memwd_* log events
  • Location:
    • stg: https://nonprod-log.gitlab.net/goto/ac0b0930-073c-11ed-af31-918941b0065a
    • prd: https://log.gprd.gitlab.net/goto/28bbf300-0287-11ed-b86b-d963a1a6788e
  • What changes to this metric should prompt a rollback: none, just informational
• Metric: gitlab_memwd_heap_frag_limit
  • Location: https://thanos-query.ops.gitlab.net/graph?g0.expr=gitlab_memwd_heap_frag_limit&g0.tab=1&g0.stacked=0&g0.range_input=1h&g0.max_source_resolution=0s&g0.deduplicate=1&g0.partial_response=0&g0.store_matches=%5B%5D
  • What changes to this metric should prompt a rollback: none, just informational
• Metric: gitlab_memwd_heap_frag_violations_total
  • Location: https://thanos-query.ops.gitlab.net/graph?g0.expr=gitlab_memwd_heap_frag_violations_total&g0.tab=1&g0.stacked=0&g0.range_input=1h&g0.max_source_resolution=0s&g0.deduplicate=1&g0.partial_response=0&g0.store_matches=%5B%5D
  • What changes to this metric should prompt a rollback: none, just informational

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.
  • 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.