I was after the same issue (I was using reference runner job server, but same error message), had some clue but no conclusion yet.
The gradle task hangs because the job server isn't able to launch the docker container.
./gradlew :beam-sdks-python:portableWordCount -PjobEndpoint=localhost:8099
[CHAIN MapPartition (MapPartition at 36write/Write/WriteImpl/DoOnce/Impulse.None/beam:env:docker:v1:0) -> FlatMap (FlatMap at 36write/Write/WriteImpl/DoOnce/Impulse.None/beam:env:docker:v1:0/out.0) (8/8)] INFO org.apache.beam.runners.fnexecution.environment.DockerEnvironmentFactory - Still waiting for startup of environment tweise-docker-apache.bintray.io/beam/python:latest
for worker id 1
Unfortunately this isn't covered by tests yet. Is anyone aware what change may have caused this or looking into resolving it?