The Docker image here is actually an Accumulo image with the Gaffer iterators bundled in. When run with cocker-compose though, it will provide you a full accumulo ecosystem complete with hdfs and a Gaffer REST API
You can build the gchq/gaffer image using docker-compose:
docker-compose build
To add your own libraries into the build, you can add files to the /files directory these will be added to accumulo's /opt/accumulo/lib/ext directory
docker-compose up
Access the HDFS NameNode web UI at: http://localhost:9870
Access the Accumulo Monitor UI at: http://localhost:9995
Access the Gaffer Web UI at: http://localhost:8080/ui/
Access the Gaffer REST API at: http://localhost:8080/rest/