[PRDSUB] Grow the customersdot production VM size

Production Change

Change Summary

As a mitigation for avoiding OOM on customers.gitlab.com as seen in https://gitlab.com/gitlab-com/gl-infra/production/-/issues/7589 we want to increase the memory of this node. Since it's a single node we'll require downtime to change the machine type.

Related MR for updating Terraform: https://ops.gitlab.net/gitlab-com/gl-infra/config-mgmt/-/merge_requests/4068

This is being done manually because our Terraform uses exceptions to not modify instance types, so changes there have no effect on existing VMs.

Change Details

1. Services Impacted - ServiceCustomersDot
2. Change Technician - @cmcfarland
3. Change Reviewer - @msmiley
4. Time tracking - 15 minutes
5. Downtime Component - 5 minutes

Detailed steps for the change

Change Steps - steps to take to execute the change

Estimated Time to Complete (mins) - 15

• Set label changein-progress /label ~change::in-progress
• Create disk snapshot of customers VM data disk

gcloud --project gitlab-subscriptions-prod compute snapshots create prod7591 --source-disk customers-01-inf-prdsub --source-disk-zone us-east1-c

• Stop prdsub customers VM

gcloud --project gitlab-subscriptions-prod compute instances stop customers-01-inf-prdsub

• Change prdsub customers VM size/type

gcloud --project gitlab-subscriptions-prod compute instances set-machine-type customers-01-inf-prdsub --machine-type n1-standard-8

• Start prdsub customers VM

gcloud --project gitlab-subscriptions-prod compute instances start customers-01-inf-prdsub

• 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) - 20

• If the machine type change does not work, we can just start the VM up again and verify it's returned to operating status.
• If the machine type change causes the system to not start or start with missing data, we should stop the VM, and replace the disk with the snapshot copy (and possibly revert the machine type change).
• Set label changeaborted /label ~change::aborted

Monitoring

Key metrics to observe

• Metric: Request rate, error rate, apdex
  • Location: https://dashboards.gitlab.net/d/customersdot-main/customersdot-overview
  • What changes to this metric should prompt a rollback: Ensure that after the reboot, requests are arriving at roughly the same rate, and error rate is comparably low. Apdex may be temporarily worse since the machine will start with a cold cache.
• Metric: Host memory capacity
  • Location: thanos query
  • What changes to this metric should prompt a rollback: Ensure that after the reboot, memory capacity has doubled.

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.