my question is basically a combination of Access Docker socket within container and Accessing docker host from (jenkins) docker container
to run Jenkins fully dockerized including dynamic slaves and being able to create docker-containers within the slaves.
Except for the last part everything is already working thanks to https://github.com/maxfields2000/dockerjenkins_tutorial if the Unix-docker-sock is properly exposed to the Jenkins master.
unlike the slaves which are provisioned dynamically, the master is started via docker-compose and thus has proper access to the UNIX socket.
For the slaves which are spawned dynamically, this approach does not work. I tried to forward the access to docker like
VOLUME /var/run/docker.sock
VOLUME /var/lib/docker
during building the image. Unfortunately so far I get a Permission denied (socket: /run/docker.sock) when trying to access to docker.sock in the slave which was created like: https://gist.github.com/geoHeil/1752b46d6d38bdbbc460556e38263bc3
The strange thing is: the user in the slave is root.
So why do I not have access to the docker.sock? Or how could I burn in the --privileged flag so that the permission denied problem would go away?
With docker 1.10 a new User namespace is introduced, thus sharing docker.sock isn't enough, as root inside the container isn't root on the host machine anymore. I recently played with Jenkins container as well, and I wanted to build containers using the host docker engine. The steps I did are:
Find group id for docker group:
$ id
..... 999(docker)
Run jenkins container with two volumes - one contains the docker client executable, the other shares the docker unix socket. Note how I use --group-add to add the container user to the docker group, to allow access:
docker run --name jenkins -tid -p 8080:8080 --group-add=999 -v /path-to-my-docker-client:/home/jenkins/docker -v /var/run/docker.sock:/var/run/docker.sock jenkins
Tested and found it indeeds work:
docker exec -ti jenkins bash
./docker ps
See more about additional groups here
Another approach would be to use --privileged flag instead of --group-add, yet its better to use avoid it if possible