fix for #60120

doc/administration/integration/plantuml.md

@@ -54,6 +54,21 @@ http://localhost:8080/plantuml
 
 you can change these defaults by editing the `/etc/tomcat7/server.xml` file.
 
+### Making local PlantUML accessible using custom GitLab setup
+
+The PlantUML server runs locally on your server, so it is not accessible
+externally. As such, it is necessary to catch external PlantUML calls and 
+redirect them to the local server. 
+
+The idea is to redirect each call to `https://gitlab.example.com/-/plantuml/`
+to the local PlantUML server `http://localhost:8080/plantuml`.
+
+To enable the redirection, add the following line in `/etc/gitlab/gitlab.rb`:
+
+```ruby
+nginx['custom_gitlab_server_config'] = "location /-/plantuml { \n    proxy_cache off; \n    proxy_pass  http://127.0.0.1:8080; \n}\n"
+```
+
 ## GitLab
 
 You need to enable PlantUML integration from Settings under Admin Area. To do
@@ -62,7 +77,7 @@ that, login with an Admin account and do following:
 - In GitLab, go to **Admin Area > Settings > Integrations**.
 - Expand the **PlantUML** section.
 - Check **Enable PlantUML** checkbox.
-- Set the PlantUML instance as **PlantUML URL**.
+- Set the PlantUML instance as `https://gitlab.example.com/-/plantuml/`.
 
 ## Creating Diagrams