PlantUML & GitLab

Introduced in GitLab 8.16.

When PlantUML integration is enabled and configured in GitLab we are able to create simple diagrams in AsciiDoc and Markdown documents created in snippets, wikis, and repositories.

PlantUML Server

Before you can enable PlantUML in GitLab; you need to set up your own PlantUML server that will generate the diagrams.

Docker

With Docker, you can just run a container like this:

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

The PlantUML URL will be the hostname of the server running the container.

When running GitLab in Docker, it will need to have access to the PlantUML container. The easiest way to achieve that is by using Docker Compose.

A simple docker-compose.yml file would be:

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

In this scenario, PlantUML will be accessible for GitLab at the URL http://plantuml:8080/.

Debian/Ubuntu

Installing and configuring your own PlantUML server is easy in Debian/Ubuntu distributions using Tomcat.

First you need 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

The above sequence of commands will generate a WAR file that can be deployed using Tomcat:

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

Once the Tomcat service restarts the PlantUML service will be ready and listening for requests on port 8080:

http://localhost:8080/plantuml

you can change these defaults by editing the /etc/tomcat8/server.xml file.

Note that the default URL is different than when using the Docker-based image, where the service is available at the root of URL with no relative path. Adjust the configuration below accordingly.

Making local PlantUML accessible using custom GitLab setup

The PlantUML server runs locally on your server, so it is not accessible externally by default. 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://plantuml:8080/ or http://localhost:8080/plantuml/, depending on your setup.

To enable the redirection, add the following line in /etc/gitlab/gitlab.rb:

# 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"

To activate the changes, run the following command:

sudo gitlab-ctl reconfigure

Note that the redirection through GitLab must be configured when running GitLab with TLS due to PlantUML's use of the insecure HTTP protocol. Newer browsers such as Google Chrome 86+ do not load insecure HTTP resources on a page served over HTTPS.

Security

PlantUML has features that allows fetching network resources.

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

If you self-host the PlantUML server, network controls should be put in place to isolate it.

GitLab

You need to enable PlantUML integration from Settings under Admin Area. To do that, login with an Admin account and do following:

In GitLab, go to Admin Area > Settings > General.
Expand the PlantUML section.
Check Enable PlantUML checkbox.
Set the PlantUML instance as https://gitlab.example.com/-/plantuml/.

NOTE: If you are using a PlantUML server running v1.2020.9 and above (for example, plantuml.com), set the PLANTUML_ENCODING environment variable to enable the deflate compression. On Omnibus, this can be done set in /etc/gitlab.rb:

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

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

Creating Diagrams

With PlantUML integration enabled and configured, we can start adding diagrams to our AsciiDoc snippets, wikis, and repositories using delimited blocks:

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
```
You can also use the uml:: directive for compatibility with sphinxcontrib-plantuml, but please note that we currently only support the caption option.

The above blocks will be converted to an HTML image tag with source pointing to the PlantUML instance. If the PlantUML server is correctly configured, this should render a nice diagram instead of the block:

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

Inside the block you can add any of the supported diagrams by PlantUML such as Sequence, Use Case, Class, Activity, Component, State, and Object diagrams. You do not need to use the PlantUML diagram delimiters @startuml/@enduml as these are replaced by the AsciiDoc plantuml block.

Some parameters can be added to the AsciiDoc block definition:

format: Can be either png or svg. Note that svg is not supported by all browsers so use with care. The default is png.
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 will always use PNG format.