a.k.a. DinJinD

Trying to build Docker images from your Jenkins which is itself in a Docker container and still seeing Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running? message? A solution is here!

If you want a Jenkins Docker image in which you can build Docker images, it is a bit tricky:

• To be able to run Docker commands in a Docker container, you need to use the wrapdocker script from DinD project and run your container with the --privileged flag.
• Because you cannot directly run multiple services in a container, you have to use a tool (Supervisor here) which will manage and run both Jenkins and Docker services. The container will then run Supervisor, which will start Jenkins and Docker.

• Build image:

docker build -t docker-in-jenkins-in-docker .

• Run container:

docker run --privileged -it -p 8080:8080 docker-in-jenkins-in-docker

• Open Jenkins at http://localhost:8080/

If you have a specific DNS configuration (like nameserver and search entries in /etc/resolv.conf configuration), you should forward this DNS configuration to the Docker daemon. To do this, you have to create and configure /etc/docker/daemon.json file and specify dns and dns-search options. For example, you can add these lines to your Dockerfile after the Docker installation:

RUN mkdir -p /etc/docker
RUN touch /etc/docker/daemon.json
RUN echo '{"dns":["8.8.8.8","a.b.c.d"],"dns-search":["search1.domain","search2.domain"]}' > /etc/docker/daemon.json

• https://github.com/jpetazzo/dind
• https://blog.docker.com/2013/09/docker-can-now-run-within-docker/
• https://blog.jayway.com/2015/03/14/docker-in-docker-with-jenkins-and-supervisord/