As explained on the PlayPen deployer docs, we created a Docker image based on hugmanrique/playpen which git pulls the PlayPen packages (to guarantee an up-to-date packaged PlayPen P3 asset), packages the produced Maven artifacts with playpen-p3 and finally deploys them to the set network.
The Docker image should be rebuilt whenever a large change to the playpen-packages repo is made to ensure git pull times are fast (remember the packages repo contains maps and other produced artifacts such as Spigot or ProtocolLib). Please take a look at the Building the image section on the PlayPen Deployer repo to obtain details on how to build and tag the image with docker. Please note this image must be kept private as it contains a read-only access token to the PlayPen packages repo, so make sure you don't push it to any Docker repository.
If you ever push the Docker image to any Docker repository (even if it's private), please contact @Hugo to generate a new one and remove the old one.