Add note on external url setting for HA clusters.

doc/administration/high_availability/gitlab.md

@@ -71,6 +71,12 @@ for each GitLab application server in your environment.
     gitlab_rails['redis_password'] = 'Redis Password'
     ```
     
+    > **Note:** To maintain uniformity of links across HA clusters, the `external_url` 
+    on the master as well as all secondary application servers should point to the 
+    eventual url that users will use to access GitLab. In a typical HA setup, 
+    this will be the url of the load balancer which will route traffic to all 
+    GitLab application servers in the HA cluster. 
+
 1. Run `sudo gitlab-ctl reconfigure` to compile the configuration.
 
 ## Primary GitLab application server