2022-10-05: Rollout PREVENT_LOAD_BALANCER_RETRIES_IN_TRANSACTION environment variable
Production Change
Change Summary
With Do not retry queries if a transaction is open (gitlab-org/gitlab!90447 - merged) we aim to fix DB load balancer: Automatic retries may leak qu... (gitlab-org/gitlab#220242 - closed). As this is a change to delicate part of our load-balancing system, and has the potential to impact many services, we've put it behind an ENV variable so that we can roll it out incrementally.
We did not use feature flag, as the code to check feature flags runs through this code path when querying feature flag state from the database, leading to infinite recursion.
Using an environment variable, combined with rolling it out to the canary stage first, gives us an easy way back, by disabling the canary stage.
Change Details
- Services Impacted - ServiceWeb ServiceAPI ServiceGitLab Rails
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Change Technician -
@krasio
,@stomlinson
@f_santos - Change Reviewer - @f_santos
- Time tracking - unknown
- Downtime Component - none
Detailed steps for the change
Change Steps - steps to take to execute the change
Estimated Time to Complete (mins) - Estimated Time to Complete in Minutes
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Set label changein-progress /label ~change::in-progress
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Apply to staging-canary
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Merge the MR that adds the environment variable to gstg-cny
- gitlab-com/gl-infra/k8s-workloads/gitlab-com!2244 (merged). -
Wait for the deployment to complete and verify
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-
Apply to staging
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Merge the MR that adds the environment variable to gstg
- gitlab-com/gl-infra/k8s-workloads/gitlab-com!2245 (merged). -
Wait for the deployment to complete and verify
-
-
Apply to production-canary
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Merge the MR that adds the environment variable to gprd-cny
- gitlab-com/gl-infra/k8s-workloads/gitlab-com!2354 (merged). -
Wait for the deployment to complete and verify
-
-
Apply to production
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Merge the MR that adds the environment variable to gprd
- gitlab-com/gl-infra/k8s-workloads/gitlab-com!2372 (merged). -
Wait for the deployment to complete and verify
-
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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
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In case we want to rollback the canary stage of environment we can disable it with -
Disable production-canary - /chatops run canary --disable --production
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Disable staging-canary - /chatops run canary --disable
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In case we want to rolling back the change from main stage of an environment, we need to revert the MR that introduced the environment variable and apply the configuration change, here is a revert MR - gitlab-com/gl-infra/k8s-workloads/gitlab-com!2384 (closed). -
Set label changeaborted /label ~change::aborted
Monitoring
How to know if it worked
Transaction leaks occurrences
If everything is working as expected these should disappear:
This is not a common event for staging
, so it may be tricky to verify this quickly.
read_write
retry occurrences
With fixing transaction leaks, we may see increase in read_write_retry
events:
We started to log this just recently, so there may not be data further back in the past.
Key metrics to observe
-
Metric: rails_primary_sql SLI Apdex
- Location: https://dashboards.gitlab.net/d/patroni-main/patroni-overview?orgId=1&viewPanel=2409561530&from=now-6h&to=now
- What changes to this metric should prompt a rollback: Any drop in apdex
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Metric: PostgreSQL Overview dashboard
- Location: https://dashboards.gitlab.net/d/000000144/postgresql-overview?orgId=1&from=now-6h&to=now
- What changes to this metric should prompt a rollback: Any deviation from the normal state
Change Reviewer checklist
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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.
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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
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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.