Build the independent post-deploy migration pipeline

As part of &585 (closed).

After having visibility of the pending post-deploy migrations, we need to build a post-deploy migration pipeline that is triggered independently from the coordinated pipeline.

This pipeline:

• Notifies the start/ending of the post-deployment migrations in gstg and gprd
• Executes the post-deployment migrations if production is healthy
• Is executed independently from the coordinated pipeline

Slides: https://docs.google.com/presentation/d/1SjdeV3_DIYmqUnSHfdrx9kG0laVnsjI995B8skkkE38/edit?usp=sharing

Implementation details

Coordinated pipeline

• Implement a production check that is executed before the post-migrations are executed gitlab-org/release-tools!1752 (merged)
• Implement the post-deploy migration CI gitlab-org/release-tools!1747 (merged) / gitlab-org/release-tools!1777 (merged)
• Update the post-deploy migrations notifications. gitlab-org/release-tools!1758 (merged)
  • These notifications differ since they will not point out to a DEPLOY_VERSION
  • Notifications should notify the start/end (whether is success or fail) of the post-deploy migrations in gstg and gprd.

Deployer

• Ensure the post-deployment migrations can be executed without a DEPLOY_VERSION https://ops.gitlab.net/gitlab-com/gl-infra/deployer/-/merge_requests/473/diffs
• Ensure the post-deployment migration execution locks the environment https://ops.gitlab.net/gitlab-com/gl-infra/deployer/-/merge_requests/477

Other

• Create a pipeline schedule that executes this independent post-deploy pipeline (later a ChatOps command can be built) https://ops.gitlab.net/gitlab-org/release/tools/-/pipeline_schedules/251/edit

Follow-ups

• Remove the post-migration jobs from the coordinated pipeline #2353 (closed)
• Remove the deploy_version dependency from the post-deployment classes #2354 (closed)
• Post a message on release/tasks when the post-deploy pipeline is executed #2346 (closed)