Jenkins-node as docker container

Question

The jenkins-node is a docker-container on which the jobs are run. A jenkins-job running in the dockerized jenkins-node checks the project of svn/git and runs the build and test in other docker-containers launched by the job. In doing so the jenkins-job mounts via "docker run -v : ..." files/directories from the checked out project into the build-container. This sounds like docker-in-docker, but according to http://jpetazzo.github.io/2015/09/03/do-not-use-docker-in-docker-for-ci/ docker-in-docker is not good in ci. With the recommended approach (mount the hosts docker-socket into the jenkins-node container) I'm facing the problem that the mounted files in the build-container appear as empty direcotries. I think it's because these files are not known in the host (they are checked out inside the jenkins-node container). Providing the --privileged flag doesn't help this way.

However the 'evil' docker-in-docker approach works fine with this scenario. Am I doing s.th. wrong or is docker-in-docker the way to go here?

Answer 1

With "expose the docker socket" approach all volume paths are going to be relative to the host. So if you need to access something in the jenkins-node container you have two options:

• make sure the checkout directory is a volume, and use --volumes-from jenkins-node as an argument to all the other docker containers. From your question it sounds like the containers created by the test suite would be configured from the app repos, so this is probably not a good option.
• make the checkout directory a host mounted volume -v /git/checkouts:/path/in/jenkins-node/container when you start jenkins-node. That way the files will actually end up on the host (not in the jenkins-node container), and you'll be able to access them a the host path.

I would also say that the article you're referencing is more of a caution. dind is still done quite a bit, sometimes it's even necessary. It's not the worst thing ever, just be aware that it's not a silver bullet and does come with it's own set of issues/problems.