Finally I found some time to investigate running Jenkins in a Docker container. There is an Official Jenkins Repository on the Docker Hub so I started by pulling the latest version:

docker pull jenkins

More information about this image can be found in the Jenkins website Official Jenkins LTS docker image blog post by Michael Neale. Curiously this post also has a link to cloudbees/jenkins-ci.org-docker GitHub repository which contained a lot of useful information.

Running the official Jenkins image could not be simpler:

docker run -p 8080:8080 jenkins

At this point I decided to implement a Data Volume Container to provide simple back-up capabilites and to experiment with extending the official image to include some plugins via the core-support plugin format.

Adding a Data Volume Container

Creating a named data volume container was pretty simple:

docker create -v /var/jenkins_home --name jenkins-dv jenkins

This command uses the ‘/var/jenkins_home’ directory volume as per the official image and provides a name ‘jenkins-dv’ to identify the data volume container.

To use the data volume container with an image you use the ‘–volumes-from’ flag to mount the ‘/var/jenkins_home’ volume in another container:

docker run -d -p 8080:8080 --volumes-from jenkins-dv --name myjenkins jenkins

Once you have the docker container running you can go to http://localhost:8080 to see the Jenkins instance running. This instance is storing data in the volume container you set up previously, so if you set up a job and stop the container the data is persisted. To prove this you can stop and remove the ‘myjenkins’ container and start a second container:

docker run -d -p 8080:8080 --volumes-from jenkins-dv --name myjenkins2 jenkins

Once more hitting http://localhost:8080 will show your Jenkins instance but this time any jobs you set up and that were stored to the data volume container should be present.

Building a Custom Image including some Plugins

Deriving a new Dockerfile from the official image makes it simple to include some defined plugins. As per the documentation in the Installing more tools section of the cloudbees documentation I created a Dockerfile with the following content:

1 2 3 4 5 FROM jenkins MAINTAINER Pete Sellars <psellars@gmail.com> COPY plugins.txt /usr/share/jenkins/plugins.txt RUN /usr/local/bin/plugins.sh /usr/share/jenkins/plugins.txt

This expects a ‘plugins.txt’ file that in my case looked like this:

1 2 dockerhub:1.0 disk-usage:0.25

I then built my derived image in the folder containing both these files using the following command:

docker build -t psellars/jenkins .

Using this image I was then able to create a container that used the previously created data volume container:

docker run -d -p 8080:8080 --volumes-from jenkins-dv --name custom-jenkins psellars/jenkins

This container will have the DockerHub Plugin and Disk Usage Plugin installed and any jobs set up in the previous containers. You could create a data volume container based on the custom image - and I would recommend this as a task to be done.

Backing Up

To backup the data from the volume container is simple to. Simply run:

docker cp jenkins-dv:/var/jenkins_home /tmp/jenkins-backup

Once this operation is complete on your local machine in ‘/tmp/jenkins-backup’ you will find a ‘jenkins_home’ directory backup. You could now use this to populate a new data volume container.