Skip to content

[GSTG][Sec Decomp] - Phase 4 Rollback - Swap pgbouncer-sec read traffic back to main

Production Change

Change Summary

Summary: In this phase we need to swap pgbouncer-sec read traffic from patroni-sec back to patroni-main.

Now that both read/write traffic is enabled on pgbouncer-sec we need to update our pgbouncer configuration to begin sending read traffic back to patroni-main instead of patroni-sec. This will ensure we can perform our physical to logical switchover without issue

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 began serving reads from the patroni-sec replicas (synced via cascading replication) to validate queries are working as expected.

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 ServicePatroniSec
  2. Change Technician - @zbraddock
  3. Change Reviewer - @jjsisson
  4. Scheduled Date and Time (UTC in format YYYY-MM-DD HH:MM) - 2025-04-01 21:00
  5. Time tracking - 2h
  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) - 120

  • 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 k8s-workload node rollout

Note this is a combined phase from the previous phases 4.2 to 4.4

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 }
=> "main_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-sec.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