Document upgrade path for Geo nodes to PostgreSQL 10.0

Problem to solve

Further details

GitLab %12.0 will upgrade the underlying PostgreSQL version to 10.0 automatically (see omnibus-gitlab#4299 (closed)); however, the upgrade will be skipped for nodes with Geo configuration. We need to document the required steps needed to take on Geo primary and secondaries to upgrade from any installation prior to %12.0 to %12.0.

Proposal

Currently, the steps listed by @brodock in https://gitlab.com/gitlab-org/gitlab-ee/issues/12092 are roughly:

• Disable PostgreSQL automatic upgrade
• Upgrade GitLab to 12.0
• Schedule downtime on secondary nodes
• Put secondary in maintenance mode (halt access)
• Upgrade primary
• Trigger postgresql upgrade on secondary
• Backup/restore database from primary
• Enable access again

These steps need to be clearly defined and added to the Administrator documentation for Geo: https://docs.gitlab.com/ee/administration/geo/replication/updating_the_geo_nodes.html

Who can address the issue

Other links/references