Merge branch 'docs-update-geo' into 'master'

Docs: update Geo with upgrade instructions

See merge request !2491

doc/gitlab-geo/README.md

@@ -113,6 +113,10 @@ If you installed GitLab from source:
 
 [install-ee-source]: https://docs.gitlab.com/ee/install/installation.html "GitLab Enterprise Edition installation from source"
 
+## Configuring GitLab Geo
+
+Read through the [GitLab Geo configuration](configuration.md) documentation.
+
 ## Updating the Geo nodes
 
 Read how to [update your Geo nodes to the latest GitLab version](updating_the_geo_nodes.md).

doc/gitlab-geo/configuration.md

@@ -282,6 +282,19 @@ Host example.com                    # The FQDN of the primary Geo node
   IdentityFile ~/.ssh/mycustom.key  # The location of your private key
 ```
 
+### Upgrading Geo
+
+To avoid having to maintain consistency of the `authorized_keys` file for SSH access,
+we encourage all **Geo** users to
+[switch to SSH key lookups via the database](ssh.md).
+This will be necessary once Geo system hooks are removed.
+
+We highly recommend using replication slots. The easiest way to do this in Omnibus is the following:
+  1. Install GitLab on the primary server
+  1. Run `gitlab-ctl reconfigure` and `gitlab-ctl restart postgresql`. This will enable replication slots on the primary database.
+  1. Install GitLab on the secondary server.
+  1. Re-run the [database replication process](database.md#step-3-initiate-the-replication-process).
+
 ## Troubleshooting
 
 See the [troubleshooting document](troubleshooting.md).