To use it, you not only need to configure the diagrams plugin but also to install graphviz on your system. If you want to use one of the other text-2-diagram tools supported by the plugin (like mermaid), you also have to install this one.
With kroki.io, there is an easier way to solve this. The dev-team behind kroki has taken the idea of the plantuml server to the next level. It takes an optionally zipped and base64 encoded diagram definition and returns the rendered diagram. And it does so not only for plantuml, but also for all the other diagram types supported by the asciidoctor diagram extension!
But I don’t want to use a public server!
Yes, if you don’t work on an open-source problem, this might be a concern, but the kroki team has also taken care of this. Kroki not only comes as ready to use public server, but you can also use it ready to run as a fat jar or as docker image.
To switch to kroki, you only have to point your diagram extension to the server by adding two attributes to your document:
:diagram-server-url: https://yourserver :diagram-server-type: kroki_io
PS: if you’ve used the plantuml server in the past - kroki even works as a replacement for it.