PlantUML

Tier: Free, Premium, Ultimate Offering: Self-managed

With the PlantUML integration, you can create diagrams in snippets, wikis, and repositories. This integration is enabled on GitLab.com for all SaaS users and does not require any additional configuration.

To set up the integration on a self-managed instance, you must configure your PlantUML server.

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 files with the extension .md: 

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

    For additional acceptable extensions, review the languages.yaml file.

  • AsciiDoc files with the extension .asciidoc, .adoc, or .asc: 

    [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:

  • 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 8005:8080 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:8005/: 

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    rewrite ^/-/plantuml/(.*) /$1 break;\n proxy_cache off; \n    proxy_pass  http://plantuml:8005/; \n}\n"

  plantuml:
    image: 'plantuml/plantuml-server:tomcat'
    container_name: plantuml
    ports:
     - "8005:8080"

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/
  • http://plantuml:8005/
  • http://localhost:8005/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  rewrite ^/-/plantuml/(.*) /$1 break;\n  proxy_cache off; \n    proxy_pass  http://plantuml:8005/; \n}\n"

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

    sudo gitlab-ctl reconfigure

Debian/Ubuntu

You can install and configure a PlantUML server in Debian/Ubuntu distributions using Tomcat or Jetty.

Prerequisites:

  • JRE/JDK version 11 or later.
  • (Recommended) Jetty version 11 or later.
  • (Recommended) Tomcat version 10 or later.

Installation

PlantUML recommends to install Tomcat 10 or above. The scope of this page only includes setting up a basic Tomcat server. For more production-ready configurations, see the Tomcat Documentation.

  1. Install JDK/JRE 11: 

    sudo apt update
sudo apt-get install graphviz default-jdk git-core

  2. Add a user for Tomcat: 

    sudo useradd -m -d /opt/tomcat -U -s /bin/false tomcat

  3. Install and configure Tomcat 10: 

    wget https://dlcdn.apache.org/tomcat/tomcat-10/v10.1.15/bin/apache-tomcat-10.1.15.tar.gz -P /tmp
sudo tar xzvf /tmp/apache-tomcat-10*tar.gz -C /opt/tomcat --strip-components=1
sudo chown -R tomcat:tomcat /opt/tomcat/
sudo chmod -R u+x /opt/tomcat/bin

  4. Create a systemd service. Edit the /etc/systemd/system/tomcat.service file and add: 

    [Unit]
Description=Tomcat
After=network.target

[Service]
Type=forking

User=tomcat
Group=tomcat

Environment="JAVA_HOME=/usr/lib/jvm/java-1.11.0-openjdk-amd64"
Environment="JAVA_OPTS=-Djava.security.egd=file:///dev/urandom"
Environment="CATALINA_BASE=/opt/tomcat"
Environment="CATALINA_HOME=/opt/tomcat"
Environment="CATALINA_PID=/opt/tomcat/temp/tomcat.pid"
Environment="CATALINA_OPTS=-Xms512M -Xmx1024M -server -XX:+UseParallelGC"

ExecStart=/opt/tomcat/bin/startup.sh
ExecStop=/opt/tomcat/bin/shutdown.sh

RestartSec=10
Restart=always

[Install]
WantedBy=multi-user.target

    JAVA_HOME should be the same path as seen in sudo update-java-alternatives -l.

  5. To configure ports, edit your /opt/tomcat/conf/server.xml and choose your ports. Avoid using port 8080, as Puma listens on port 8080 for metrics. 

    <Server port="8006" shutdown="SHUTDOWN">
...
    <Connector port="8005" protocol="HTTP/1.1"
...

  6. Reload and start Tomcat: 

    sudo systemctl daemon-reload
sudo systemctl start tomcat
sudo systemctl status tomcat
sudo systemctl enable tomcat

    The Java process should be listening on these ports: 

    root@gitlab-omnibus:/plantuml-server# netstat -plnt | grep java
tcp6       0      0 127.0.0.1:8006          :::*                    LISTEN      14935/java
tcp6       0      0 :::8005                 :::*                    LISTEN      14935/java

  7. Modify your NGINX configuration in /etc/gitlab/gitlab.rb. Ensure the proxy_pass port matches the Connector port in server.xml: 

    nginx['custom_gitlab_server_config'] = "location /-/plantuml {
    rewrite ^/-/(plantuml.*) /$1 break;
    proxy_set_header  HOST               $host;
    proxy_set_header  X-Forwarded-Host   $host;
    proxy_set_header  X-Forwarded-Proto  $scheme;
    proxy_cache off;
    proxy_pass http://localhost:8005/plantuml;
}"

  8. Reconfigure GitLab to read the new changes: 

    sudo gitlab-ctl reconfigure

  9. Install PlantUML and copy the .war file:

    Use the latest release of plantuml-jsp (example: plantuml-jsp-v1.2023.12.war). For context, see this issue. 

    wget -P /tmp https://github.com/plantuml/plantuml-server/releases/download/v1.2023.12/plantuml-jsp-v1.2023.12.war
sudo cp /tmp/plantuml-jsp-v1.2023.12.war /opt/tomcat/webapps/plantuml.war
sudo chown tomcat:tomcat /opt/tomcat/webapps/plantuml.war
sudo systemctl restart tomcat

The Tomcat service should restart. After the restart is complete, the PlantUML integration is ready and listening for requests on port 8005: http://localhost:8005/plantuml

To test if the PlantUML server is working, run curl --location --verbose "http://localhost:8005/plantuml/".

To change the Tomcat defaults, edit the /opt/tomcat/conf/server.xml file.

note
The 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.

404 error when opening the PlantUML page in the browser

You might get a 404 error when visiting https://gitlab.example.com/-/plantuml/, when the PlantUML server is set up in Debian or Ubuntu.

This can happen even when the integration is working. It does not necessarily indicate a problem with your PlantUML server or configuration.

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. For example, make use of PlantUML’s security profiles. 

@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 left sidebar, at the bottom, select Admin.
  3. On the left sidebar, go to Settings > General and expand the PlantUML section.
  4. Select the Enable PlantUML checkbox.
  5. Set the PlantUML instance as https://gitlab.example.com/-/plantuml/, and select 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 later, such as plantuml.com, you must set the PLANTUML_ENCODING environment variable to enable the deflate compression. In Linux package installations, you can set this value in /etc/gitlab/gitlab.rb with this command: 

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

    In GitLab Helm chart, you can set it by adding a variable to the global.extraEnv section, like this: 

    global:
extraEnv:
  PLANTUML_ENCODING: deflate

  • deflate is the default encoding type for PlantUML. To use a different encoding type, PlantUML integration requires a header prefix in the URL to distinguish different encoding types.

Troubleshooting

Rendered diagram URL remains the same after update

Rendered diagrams are cached. To see the updates, try these steps:

  • If the diagram is in a Markdown file, make a small change to the Markdown file, and commit it. This triggers a re-render.
  • Invalidate the Markdown cache to force any cached Markdown in the database or Redis to be cleared.

If you’re still not seeing the updated URL, check the following:

  • Ensure the PlantUML server is accessible from your GitLab instance.
  • Verify that the PlantUML integration is enabled in your GitLab settings.
  • Check the GitLab logs for errors related to PlantUML rendering.
  • Clear your GitLab Redis cache.