Valentine's Day for Jenkins

Using Docker - No plugins required

Last time I investigated using Docker inside the “master” container. It was pretty cool, but it was inconvenient when directories needed to be mounted to the containers. I intend to continue investigating the Docker plugins, but I felt like Jenkins needed some company for Valentines Day.

Jenkins JNLP Slaves as Docker Containers

The goal is to add a “Normal” Jenkins slave node that can connect to the master in the typical fashion. The Jenkins JNLP Agent Docker image published by jenkinsci/docker-jnlp-slave can act as a base image and provides a useful entrypoint. Any number of these slaves can be added to the docker-compose.yaml and then be available to the master. It appears that /home/jenkins/agent is intended to be used for the workdir.

Configuration

Although the entrypoint above supports command line arguments I found that it was much easier to configure the values using multiple ‘env_file’ entries. This way I can share the common variables easily and keep the “secret” out of version control. The entrypoint provided with docker-jnlp-slave was not designed to handle the scenario where the master is being launched by the same docker-compose file. The slave would attempt to connect before the master was ready and then crash. I fixed this by using a simple wrapper to the entrypoint that would keep retrying until the connection was successful.