Huginn is packaged in two docker images.
huginn/huginn multiple process image
This image runs all processes needed by Huginn in one container, when the database is not linked it will also start MySQL internally. This is great to try huginn without having to set up anything, however maintenance and backups can be difficult.
huginn/huginn-single-process multiple container image
This image runs just one process per container and thus needs at least two container to be started, one for the Huginn application server and one for the threaded background worker. It is also possible to every background worker in a separate container to improve the performance. See the PostgreSQL docker-compose configuration for an example.