docker-compose and listing volume contents

Question

Maybe I'm just not understanding correctly but I'm trying to visually verify that I have used volumes properly.

In my docker-compose I'd have something like

some-project:
  volumes:
   - /some-local-path/some-folder:/v-test

I can verify it's contents via "ls -la /some-local-path/some-folder"

In some-projects Dockerfile I'd have something like

  RUN ls -la /v-test

which returns 'No such file or directory"

Is this the correct way to use it? If so, why can't I view the contents from inside the container?

Answer 1

Everything in the Dockerfile runs before anything outside the build: block in the docker-compose.yml file is considered. The image build doesn't see volumes or environment variables that get declared only in docker-compose.yml , and it can't access other services.

In your example, first the Dockerfile tries to ls the directory, then Compose will start the container with the bind mount.

If you're just doing this for verification, you can docker-compose run a container with most of its settings from the docker-compose.yml file, but an alternate command:

docker-compose run some-project \
  ls -la /v-test

(Doing this requires that the image's CMD is a well-formed shell command; either it has no ENTRYPOINT or the ENTRYPOINT is a wrapper script that ends in exec "$@" to run the CMD . If you only have ENTRYPOINT , change it to CMD ; if you've split the command across both directives, consolidate it into a single CMD line.)