QGIS-Server-light is a python worker process which uses pyqgis to render a set of layers into an image. It is backed by Redis as a queue system. All configuration happens at runtime through a lean interface.
docker run --rm -d -p 1234:6379 --name qsl-redis redis
docker run -ti --rm --net host --name qsl opengisch/qgis-server-light:latest
In case you have local geodata which is used in your QGIS projects, you need to make it available to QGIS-Server-Light through a volume mount:
docker run -ti --rm --net host --name qsl -v <local-path-to-your-qgis-projects>:/io/data opengisch/qgis-server-light:latest
For further details and a better understanding please refer to the documentation.