Have to migrate the job https://integration.wikimedia.org/ci/job/language-screenshots-VisualEditor/ off of Nodepool and use Docker containers instead.
It uses a matrix job that populate the axis to be build from yaml files in mediawiki/extensions/VisualEditor. Then for each combination it does something like:
npm install node_modules/.bin/grunt screenshots-all bundle install bundle exec upload
The CI docker container expect to use a npm script or a rake task. So the first step is to add a npm script for 'grunt screenshots-all' and a task for 'upload'.