VOLUME declaration can result in difficult to diagnose misbehavior

[HoloRin]

By declaring the VOLUME $RABBITMQ_DATA_DIR in the base Dockerfile, (i.e.

rabbitmq/3.8/ubuntu/Dockerfile

Line 257 in 91be7cf

VOLUME $RABBITMQ_DATA_DIR

), it ensures that changes to that directory in subsequent Dockerfiles are ignored. This can cause very confusing behavior if, for instance, a user wants to add a specific erlang cookie in a new Dockerfile that inherits from this one. Additionally, if the behavior of rabbitmq-plugins were to change such that relies on modifying the data dir, the management Dockerfile would at least partially break.

[HoloRin]

https://docs.docker.com/engine/reference/builder/#volume

If any build steps change the data within the volume after it has been declared, those changes will be discarded.

I also tried redeclaring the VOLUME after making the desired changes, however the behavior remains unchanged:

FROM rabbitmq:3.8

RUN echo "test" > ${RABBITMQ_DATA_DIR}/test.txt && cat ${RABBITMQ_DATA_DIR}/test.txt

VOLUME $RABBITMQ_DATA_DIR

docker build . -t dvdt
docker run --rm -it dvdt /bin/cat /var/lib/rabbitmq/test.txt

which prints

/bin/cat: /var/lib/rabbitmq/test.txt: No such file or directory

So, I believe the only available solution is to drop the VOLUME declaration from the Dockerfile.

[wglambert]

Other discussions on removing inherent volumes in images docker-library/mongo#306, redis/docker-library-redis#140, docker-library/postgres#404, docker-library/mysql#255

docker-library/cassandra#180 (comment)

While I agree it's unfortunate Docker doesn't have a feature to disable inherited volumes, I really hesitate to add extra explicit variants that then need to be maintained to support this.

[HoloRin]

I'd like to propose #416 as a solution with minimal maintenance overhead.

[edvinkuric]

Yeah, that is a known issue: moby/moby#3639

i always had to replace the volume-command manually in a fork of that image

[lukebakken]

Closing since the behavior reported in this comment does not seem to be the case anymore.

Please see the following project for the Dockerfile I used, my environment, and a Makefile to build and run the image:

https://github.com/lukebakken/docker-library-rabbitmq-410