Docker mounting an empty directory - docker

Question

Working in Jenkinsx build container ...
I'm trying to mount a volume while in docker container. The directory get's mounted, however, the files that exist on source ( host ) directory are not present in the container.
In this case, the host is a docker container as well, so basically I'm running docker-compose from docker container.
Does anyone experienced this issue and has a solution?
Here are the results :
bash-4.2# pwd
/home/jenkins
bash-4.2# ls -l datadir/
total 4
-rw-r--r-- 1 root root 4 May 15 20:06 foo.txt
bash-4.2# cat docker-compose.yml
version: '2.3'
services:
testing-wiremock:
image: rodolpheche/wiremock
volumes:
- ./datadir:/home/wiremock
bash-4.2# df -h
Filesystem Size Used Avail Use% Mounted on
overlay 95G 24G 71G 25% /
tmpfs 7.4G 0 7.4G 0% /dev
tmpfs 7.4G 0 7.4G 0% /sys/fs/cgroup
/dev/sda1 95G 24G 71G 25% /etc/hosts
tmpfs 7.4G 4.0K 7.4G 1% /root/.m2
shm 64M 0 64M 0% /dev/shm
tmpfs 7.4G 4.0K 7.4G 1% /home/jenkins/.docker
tmpfs 7.4G 1.9M 7.4G 1% /run/docker.sock
tmpfs 7.4G 0 7.4G 0% /home/jenkins/.gnupg
tmpfs 7.4G 12K 7.4G 1% /run/secrets/kubernetes.io/serviceaccount
bash-4.2# docker-compose up -d
Creating network "jenkins_default" with the default driver
Creating jenkins_testing-wiremock_1 ... done
bash-4.2# docker ps |grep wiremock
6293dee408aa rodolpheche/wiremock "/docker-entrypoint.…" 26 seconds ago Up 25 seconds 8080/tcp, 8443/tcp jenkins_testing-wiremock_1
8db3b729c5d2 rodolpheche/wiremock "/docker-entrypoint.…" 21 minutes ago Up 21 minutes (unhealthy) 8080/tcp, 8443/tcp zendeskintegration_rest_1
bd52fb96036d rodolpheche/wiremock "/docker-entrypoint.…" 21 minutes ago Up 21 minutes (unhealthy) 8080/tcp, 8443/tcp zendeskintegration_zendesk_1
bash-4.2# docker exec -it 6293dee408aa bash
root#6293dee408aa:/home/wiremock# ls -ltr
total 8
drwxr-xr-x 2 root root 4096 May 15 20:06 mappings
drwxr-xr-x 2 root root 4096 May 15 20:06 __files

Answer 1

I could reproduce the issue by running this on a MacOS system:
First open a shell in a container that already has docker-compose installed:
docker run --rm -v $(pwd):/work -v /var/run/docker.sock:/var/run/docker.sock --workdir /work -ti tmaier/docker-compose sh
I map the current folder so that I can work with my current project as if it were on my host.
And then inside the container:
docker-compose run testing-wiremock ls -lart
Now change the docker-compose.yml to the following:
version: '2.3'
services:
testing-wiremock:
image: rodolpheche/wiremock
volumes:
- /tmp:/home/wiremock/
and run again:
docker-compose run testing-wiremock ls -lart
This will show you the contents of the /tmp directory on the host (where the docker socket actually runs). To test you can even create a folder and a file in the /tmp and run the "docker-compose run" again. You will see the new files.
Moral of the story:
If the mounted folder corresponds to an existing folder on the host where the docker daemon is actually running, then the mapping will actually work.
host -> container -> container (mounts here refer to paths on the host)
In your specific case the folder is mounted empty because the mounted path (check it by running docker-compose config) is not present on the host (host = the host running your Jenkins container, not the Jenkins container itself).