Make documented instructions on FDW optional

doc/gitlab-geo/database.md

@@ -304,10 +304,10 @@ because we have not yet configured the secondary server. This is the next step.
     connections. The certificate can only be replicated by someone with access
     to the private key, which is **only** present on the primary node.
 
-1. Configure PostgreSQL to listen on network interfaces on secondary
+1. Optional: Configure PostreSQL to enable FDW support
 
     This step is similar to how we configured the primary instance.
-    We need to enable this, even if using a single node, to enable FDW support.
+    We need to enable this, to enable FDW support, even if using a single node.
 
     Edit `/etc/gitlab/gitlab.rb` and add the following, replacing the IP
     addresses with addresses appropriate to your network configuration:
@@ -320,6 +320,9 @@ because we have not yet configured the secondary server. This is the next step.
 
     # gitlab database user's password (defined previously)
     gitlab_rails['db_password'] = 'mypassword'
+
+    # enable fdw for the geo tracking database
+    geo_secondary['db_fdw'] = true
     ```
 
 1. Test that the `gitlab-psql` user can connect to the primary's database:

doc/gitlab-geo/database_source.md

@@ -33,8 +33,7 @@ recover. See below for more details.
 
 The following guide assumes that:
 
-- You are using PostgreSQL 9.6 or later
-  which includes the
+- You are using PostgreSQL 9.6 or later which includes the
   [`pg_basebackup` tool][pgback] and improved [Foreign Data Wrapper][FDW] support.
 - You have a primary node already set up (the GitLab server you are
   replicating from), running PostgreSQL 9.6 or later, and
@@ -264,7 +263,7 @@ node.
     bundle exec rake geo:db:migrate
     ```
 
-1. Configure the [PostgreSQL FDW][FDW] connection and credentials:
+1. Optional: Configure the [PostgreSQL FDW][FDW] connection and credentials:
 
     Save the script below in a file, ex. `/tmp/geo_fdw.sh` and modify the connection
     params to match your environment.
@@ -291,6 +290,9 @@ node.
     sudo -u postgres psql -h $GEO_DB_HOST -d $GEO_DB_NAME -p $GEO_DB_PORT -c "GRANT USAGE ON FOREIGN SERVER gitlab_secondary TO $(GEO_DB_USER);"
     ```
 
+    And edit the content of `database_geo.yml` and to add `fdw: true` to
+    the  `production:` block.
+
 ### Step 4. Initiate the replication process
 
 Below we provide a script that connects the database on the secondary node to