This is a Docker image based on the Jenkins Docker image that allows users to build and test the Gerrit CI jobs automatically, based on the configuration at https://gerrit.googlesource.com/gerrit-ci-scripts/
In turn, these CI scripts are based on http://docs.openstack.org/infra/jenkins-job-builder/ -- which builds Jenkins jobs based on YAML configurations.
In this particular image, the YAML configurations are updated and jobs reloaded every 5 minutes via the Jenkins SCM trigger. These jobs are fetched from the gerrit-ci-scripts repository and automatically reloaded.
It is also possible to run the gerrit-ci-scripts-manual job and provide the legacy Change ID number and a particular revision to build: Jenkins will fetch this particular change and load any job configurations changed in this revision. Note that it will not inhibit the main gerrit-ci-scripts trigger from polling.
If you're using boot2docker, the stock drive image and memory will not be enough. I would recommend growing your boot2docker volume to at least 40GB, and perhaps adding an extra 2-4GB swap space at the end of the volume. Additionally, you may wish to increase the amount of memory allocated to your boot2docker VM to at least 3GB (4GB+ preferred). Failing to do this may result in unusual failures of the VM or build errors.
For more information on enlarging the boot2docker volume, please see: https://docs.docker.com/articles/b2d_volume_resize/