Adds documentation on how to disable Geo

New page that details the steps to be taken to disable
a Geo setup.

doc/administration/geo/replication/disable_geo.md

+---
+stage: Enablement
+group: Geo
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
+type: howto
+---
+
+# Disabling Geo **(PREMIUM ONLY)**
+
+If you want to revert to a regular Omnibus setup after a test, or you have encountered a Disaster Recovery
+situation and you want to disable Geo momentarily, you can use these instructions to disable your
+Geo setup.
+
+There should be no functional difference between disabling Geo and having an active Geo setup with
+no secondary Geo nodes if you remove them correctly.
+
+To disable Geo, follow these steps:
+
+1. [Remove all secondary Geo nodes](#remove-all-secondary-geo-nodes).
+1. [Remove the primary node from the UI](#remove-the-primary-node-from-the-ui).
+1. [Remove secondary replication slots](#remove-secondary-replication-slots).
+1. [Remove Geo-related configuration](#remove-geo-related-configuration).
+1. [(Optional) Revert PostgreSQL settings to use a password and listen on an IP](#optional-revert-postgresql-settings-to-use-a-password-and-listen-on-an-ip).
+
+## Remove all secondary Geo nodes
+
+To disable Geo, you need to first remove all your secondary Geo nodes, which means replication will not happen
+anymore on these nodes. You can follow our docs to [remove your secondary Geo nodes](./remove_geo_node.md).
+
+If the current node that you want to keep using is a secondary node, you need to first promote it to primary.
+You can use our steps on [how to promote a secondary node](../disaster_recovery/#step-3-promoting-a-secondary-node)
+in order to do that.
+
+## Remove the primary node from the UI
+
+1. Go to **{admin}** **Admin Area >** **{location-dot}** **Geo** (`/admin/geo/nodes`).
+1. Click the **Remove** button for the **primary** node.
+1. Confirm by clicking **Remove** when the prompt appears.
+
+## Remove secondary replication slots
+
+To remove secondary replication slots, run one of the following queries on your primary
+Geo node in a PostgreSQL console (`sudo gitlab-psql`):
+
+- If you already have a PostgreSQL cluster, drop individual replication slots by name to prevent
+  removing your secondary databases from the same cluster. You can use the following to get
+  all names and then drop each individual slot:
+
+  ```sql
+  SELECT slot_name, slot_type, active FROM pg_replication_slots; -- view present replication slots
+  SELECT pg_drop_replication_slot('slot_name'); -- where slot_name is the one expected from above
+  ```
+
+- To remove all secondary replication slots:
+
+  ```sql
+  SELECT pg_drop_replication_slot(slot_name) FROM pg_replication_slots;
+  ```
+
+## Remove Geo-related configuration
+
+1. SSH into your primary Geo node and log in as root:
+
+   ```shell
+   sudo -i
+   ```
+
+1. Edit `/etc/gitlab/gitlab.rb` and remove the Geo related configuration by
+   removing any lines that enabled `geo_primary_role`:
+
+   ```ruby
+   ## In pre-11.5 documentation, the role was enabled as follows. Remove this line.
+   geo_primary_role['enable'] = true
+
+   ## In 11.5+ documentation, the role was enabled as follows. Remove this line.
+   roles ['geo_primary_role']
+   ```
+
+1. After making these changes, [reconfigure GitLab](../../restart_gitlab.md#omnibus-gitlab-reconfigure)
+   for the changes to take effect.
+
+## (Optional) Revert PostgreSQL settings to use a password and listen on an IP
+
+If you want to remove the PostgreSQL-specific settings and revert
+to the defaults (using a socket instead), you can safely remove the following
+lines from the `/etc/gitlab/gitlab.rb` file:
+
+```ruby
+postgresql['sql_user_password'] = '...'
+gitlab_rails['db_password'] = '...'
+postgresql['listen_address'] = '...'
+postgresql['md5_auth_cidr_addresses'] =  ['...', '...']
+```

doc/administration/geo/replication/index.md

@@ -265,6 +265,10 @@ For an example of how to set up a location-aware Git remote URL with AWS Route53
 
 For more information on removing a Geo node, see [Removing **secondary** Geo nodes](remove_geo_node.md).
 
+## Disable Geo
+
+To find out how to disable Geo, see [Disabling Geo](disable_geo.md).
+
 ## Current limitations
 
 CAUTION: **Caution:**