This repo is using Universal Robots URSim docker available at hub.docker.com and install the latest released external_control URCap from github as well.
Build example:
docker build -t myursim --build-arg VERSION=latest .
Run example:
docker run --rm -it -p 5900:5900 -p 29999:29999 -p 30001-30004:30001-30004 myursim
More info at hub.docker.com