For WDL questions, see the WDL specification and WDL docs.
For Cromwell questions, see the Cromwell docs and please post any issues on Github.
docker images used in the "minimal WDL for joint genotyping"
For the docker image used in WDL for joint genotyping (WGS_Joint_Analysis_160909.wdl), broadinstitute/genomes-in-the-cloud:2.2.4-1469632282, is it publically available?
Also, how is the image pulled at runtime when a task is scheduled to run on some server? Is there a docker registry to "docker pull"?