PlantUML and GitLab

When PlantUML integration is enabled and configured in GitLab, you can create diagrams in snippets, wikis, and repositories. To set up the integration, you must:

  1. Configure your PlantUML server.
  2. Configure local PlantUML access.
  3. Configure PlantUML security.
  4. Enable the integration.

After completing the integration, PlantUML converts plantuml blocks to an HTML image tag, with the source pointing to the PlantUML instance. The PlantUML diagram delimiters @startuml/@enduml aren’t required, as these are replaced by the plantuml block:

  • Markdown 

    ```plantuml
Bob -> Alice : hello
Alice -> Bob : hi
```

  • AsciiDoc 

    [plantuml, format="png", id="myDiagram", width="200px"]
----
Bob->Alice : hello
Alice -> Bob : hi
----

  • reStructuredText 

    .. plantuml::
   :caption: Caption with **bold** and *italic*

   Bob -> Alice: hello
   Alice -> Bob: hi

    Although you can use the uml:: directive for compatibility with sphinxcontrib-plantuml, GitLab supports only the caption option.

If the PlantUML server is correctly configured, these examples should render a diagram instead of the code block:

Inside the block you can add any of the diagrams PlantUML supports, such as:

You can add parameters to block definitions:

  • format: Can be either png (default) or svg. Use svg with care, as it’s not supported by all browsers, and isn’t supported by Markdown.
  • id: A CSS ID added to the diagram HTML tag.
  • width: Width attribute added to the image tag.
  • height: Height attribute added to the image tag.

Markdown does not support any parameters, and always uses PNG format.

Configure your PlantUML server

Before you can enable PlantUML in GitLab, set up your own PlantUML server to generate the diagrams:

Docker

To run a PlantUML container in Docker, run this command: 

docker run -d --name plantuml -p 8080:8080 plantuml/plantuml-server:tomcat

The PlantUML URL is the hostname of the server running the container.

When running GitLab in Docker, it must have access to the PlantUML container. To achieve that, use Docker Compose. In this basic docker-compose.yml file, PlantUML is accessible to GitLab at the URL http://plantuml:8080/: 

version: "3"
services:
  gitlab:
    image: 'gitlab/gitlab-ee:12.2.5-ee.0'
    environment:
      GITLAB_OMNIBUS_CONFIG: |
        nginx['custom_gitlab_server_config'] = "location /-/plantuml/ { \n    proxy_cache off; \n    proxy_pass  http://plantuml:8080/; \n}\n"

  plantuml:
    image: 'plantuml/plantuml-server:tomcat'
    container_name: plantuml

Debian/Ubuntu

You can install and configure a PlantUML server in Debian/Ubuntu distributions using Tomcat:

  1. Run these commands to create a plantuml.war file from the source code: 

    sudo apt-get install graphviz openjdk-8-jdk git-core maven
git clone https://github.com/plantuml/plantuml-server.git
cd plantuml-server
mvn package

  2. Deploy the .war file from the previous step with these commands: 

    sudo apt-get install tomcat8
sudo cp target/plantuml.war /var/lib/tomcat8/webapps/plantuml.war
sudo chown tomcat8:tomcat8 /var/lib/tomcat8/webapps/plantuml.war
sudo service tomcat8 restart

The Tomcat service should restart. After the restart is complete, the PlantUML service is ready and listening for requests on port 8080: http://localhost:8080/plantuml

To change these defaults, edit the /etc/tomcat8/server.xml file.

noteThe default URL is different when using this approach. The Docker-based image makes the service available at the root URL, with no relative path. Adjust the configuration below accordingly.

Configure local PlantUML access

The PlantUML server runs locally on your server, so it can’t be accessed externally by default. Your server must catch external PlantUML calls to https://gitlab.example.com/-/plantuml/ and redirect them to the local PlantUML server. Depending on your setup, the URL is either of the following:

  • http://plantuml:8080/
  • http://localhost:8080/plantuml/

If you’re running GitLab with TLS you must configure this redirection, because PlantUML uses the insecure HTTP protocol. Newer browsers such as Google Chrome 86+ don’t load insecure HTTP resources on pages served over HTTPS.

To enable this redirection:

  1. Add the following line in /etc/gitlab/gitlab.rb, depending on your setup method: 

    # Docker deployment
nginx['custom_gitlab_server_config'] = "location /-/plantuml/ { \n    proxy_cache off; \n    proxy_pass  http://plantuml:8080/; \n}\n"

# Built from source
nginx['custom_gitlab_server_config'] = "location /-/plantuml { \n rewrite ^/-/(plantuml.*) /$1 break;\n proxy_cache off; \n proxy_pass http://localhost:8080/plantuml; \n}\n"

  2. To activate the changes, run the following command: 

    sudo gitlab-ctl reconfigure

Configure PlantUML security

PlantUML has features that allow fetching network resources. If you self-host the PlantUML server, put network controls in place to isolate it. 

@startuml
start
    ' ...
    !include http://localhost/
stop;
@enduml

Enable PlantUML integration

After configuring your local PlantUML server, you’re ready to enable the PlantUML integration:

  1. Sign in to GitLab as an Administrator user.
  2. On the top bar, select Menu > Admin.
  3. In the left sidebar, go to Settings > General and expand the PlantUML section.
  4. Select the Enable PlantUML check box.
  5. Set the PlantUML instance as https://gitlab.example.com/-/plantuml/, and click Save changes.

Depending on your PlantUML and GitLab version numbers, you may also need to take these steps:

  • For PlantUML servers running v1.2020.9 and above, such as plantuml.com, you must set the PLANTUML_ENCODING environment variable to enable the deflate compression. In Omnibus GitLab, you can set this value in /etc/gitlab.rb with this command: 

     gitlab_rails['env'] = { 'PLANTUML_ENCODING' => 'deflate' }

  • For GitLab versions 13.1 and later, PlantUML integration now requires a header prefix in the URL to distinguish different encoding types.