lacalvom/my-jenkins-agent-dood repository overview

⁠my-jenkins-agent-dood

my-jenkins-agent-dood is a container image created to be used as a Jenkins agent on a CI/CD server based on the image: jenkins/ssh-agent:4.13.0-jdk11 which already has the JDK11 of Java installed, and to which some more tools have been added, necessary in this use case in particular.

In this image, Maven, Google Cloud SDK, Podman and Docker CLI have been additionally installed, in order to build container images and publish them.

The Docker outside of Docker technique has been used, which consists of mapping the socket file of the daemon that is running on our Docker server /var/run/docker.sock as a volume, and thus be able to access the resources of the Docker Host.

NOTE: Depending on the environment, this can be seen as a security vulnerability, but if used judiciously in environments where it is applied it can be very useful and easier to use than other techniques. It is not usually advisable in productive environments and/or exposed to the Internet.

An important detail is that when using this technique you have to match the GID of the existing docker group on the Docker Host with the GID of the same existing group in the container.

This is accomplished by getting the GID of the existing docker group on the Docker Host prior to building the container image and passing it as an argument in its build.

To get the GID of the existing docker group on the Docker Host:

DOCKER_GID=$(getent group docker | cut -d: -f3)

To pass it as an argument to build the container image, assuming we run the command in the same directory where the Dockerfile is:

docker build --build-arg DOCKER_GID=$DOCKER_GID -t my-jenkins-agent-dood:latest .

Last but not least is the fact that for this to work properly, you have to run the container in privileged mode and map /var/run/docker.sock as a volume.

To run a container and test it:

docker run --rm -it --name myagent --privileged -v /var/run/docker.sock:/var/run/docker.sock my-jenkins-agent-dood:latest bash

For details about container creation check out the GitHub repository https://github.com/lacalvom/my-jenkins-agent-dood.git⁠