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[GSTG][Sec Decomp] - Phase 4 Rollout - Separate read and write connection for Sec from Main (shared primary host)

Production Change

NOTE: Follow-up to changeaborted rollout [GSTG][Sec Decomp] - Phase 4 Rollout - Separate... (#19491 - closed)

Change Summary

Summary: In this phase we will gradually enable the sec connection across promoted environments, allowing GitLab Rails to connect to a dedicated pgbouncer-sec deployment.

Once traffic is enabled through pgbouncer-sec we will update our pgbouncer configuration to begin sending read traffic to patroni-sec instead of patroni-main. This will allow us to validate read queries against the standby replica before rolling reads back to patroni-main.

Background: In Phase 4 of decomposition we change the rails application to start using a new connection for read-write queries. This new read-write connection will point to a new set of PGBouncer hosts (called "PGBouncer Sec"). These PGBouncer hosts will still point writes to the main Patroni cluster (as we are not yet fully ready to decompose the Sec database. Once both Read and Write traffic is configured through pgbouncer-sec, we will begin serving reads from the patroni-sec replicas (synced via cascading replication) to validate queries are working as expected.

This step effectively gets us to a point where the application thinks it is reading and writing 2 independent databases. It just happens they are still the same database which reduces risk considerably as there is no possibility of split-brain and we can easily revert if the application runs into bugs with 2 separate connections.

Prior to this we are in Phase 2 (NOTE: Phase 3 has been skipped as a no-op) where GitLab is not utilizing the new Sec Patroni cluster at all.

Accessing the rails and database consoles

Staging

  • rails: ssh $USER-rails@console-01-sv-gstg.c.gitlab-staging-1.internal
  • main db replica: ssh $USER-db@console-01-sv-gstg.c.gitlab-staging-1.internal
  • main db primary: ssh $USER-db-primary@console-01-sv-gstg.c.gitlab-staging-1.internal
  • sec db replica: ssh $USER-db-sec@console-01-sv-gstg.c.gitlab-staging-1.internal
  • sec db primary: ssh $USER-db-sec-primary@console-01-sv-gstg.c.gitlab-staging-1.internal
  • main db psql: ssh -t patroni-main-v14-102-db-gstg.c.gitlab-staging-1.internal sudo gitlab-psql
  • sec db psql: ssh -t patroni-sec-v14-102-db-gstg.c.gitlab-staging-1.internal sudo gitlab-psql

Dashboards and debugging

These dashboards might be useful during the rollout:

Staging

Destination db: sec

Source db: main

Change Details

  1. Services Impacted - ServicePatroni
  2. Change Technician - @zbraddock
  3. Change Reviewer - @rmar1
  4. Scheduled Date and Time (UTC in format YYYY-MM-DD HH:MM) - 2025-03-27 20:00 UTC
  5. Time tracking - 6h
  6. Downtime Component - 0h

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) - 360

  • Verify with @sre-oncall and @release-managers that there are no blockers in gstg currently
  • Set label changein-progress /label ~change::in-progress

4.1 Console node rollout

4.2 GSTG node rollout

Note this is a combined phase from the previous phases 4.2 to 4.4. To avoid confusion, I've left the total phase names the same so we go straight from 4.2 to 4.5

  • Switchover gstg configuration to new pgbouncer-sec
  • Verify connectivity, monitor pgbouncer connections
  • Observe logs and prometheus for errors
  • Promote chef database connection configuration to gstg-base) setting sec to new patroni-sec-v16 DB. Writes will continue to go through PGBouncer host to main and reads to sec replicas.
    • merge chef MR
    • Ensure database_tasks: false is set for gstg-base-deploy-node.json to prevent migrations from being ran for sec DB, to be unset in Phase 7 (see note)
  • Execute Database::MonitorLockedTablesWorker.perform_async on the write console to run the table locker code. Check elastic search logs for confirmation of execution.
  • Monitor for signs of increased error rate / and or attempt to interact with staging via the UI. If you're able to login or create any records associated with the main DB then there should be no locking concerns.

4.2.1 Observable logs

All logs will split db_*_count metrics into separate buckets describing each used connection:

4.2.2. Observable prometheus metrics

4.5 Verify read traffic to patroni-sec

  1. ssh to read-write console

    • ssh $USERNAME-rails@console-01-sv-gstg.c.gitlab-staging-1.internal

  2. run chef-client to sync changes

  3. Simple checks if application sees a proper configuration (on read-write console). Expected: sec load balancer and sec_replica for read connection

    [1] pry(main)> ApplicationRecord.load_balancer.name
=> :main
[2] pry(main)> Gitlab::Database::SecApplicationRecord.load_balancer.name
=> :sec
[3] pry(main)> ApplicationRecord.connection.pool.db_config.name
=> "main"
[4] pry(main)> Gitlab::Database::SecApplicationRecord.connection.pool.db_config.name
=> "sec"
[5] pry(main)> Gitlab::Database::SecApplicationRecord.load_balancer.read { |connection| connection.pool.db_config.name }
=> "sec_replica"
[6]  Gitlab::Database::SecApplicationRecord.load_balancer.read_write { |connection| connection.pool.db_config.name }
=> "sec"

Rollback

Rollback steps - steps to be taken in the event of a need to rollback this change

Estimated Time to Complete (mins) - 90

  • Switchover gstg deploy node config back
  • Switchover gstg configuration back to pgbouncer.int.gstg.gitlab.net
  • Set label changeaborted /label ~change::aborted

Monitoring

Key metrics to observe

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.
Edited by Zoe Braddock