Docker Image

For users who do not want to provision an entire system to run a Jenkins slave there exists a Docker image which can quickly get a Jenkins Swarm connected instance to run.

Source Image

For every release of cinch that is made, a version of the Docker container is pushed to Docker Hub. Multiple tags are pushed for each Cinch release. They are named by combining source information image along with the version of Cinch used to build them.

Currently there are images built off of

• centos:7
• centos:6

These get tagged into the Cinch image repository as

• redhatqecinch/jenkins_slave:cent7-0.5.2
• redhatqecinch/jenkins_slave:cent6-0.5.2

This indicates two images, one based on the centos:7 image and one based off the centos:6 image. Both of them are built by the version 0.5.2 release of Cinch.

Image Options

As with the rest of Cinch, there are some customizable image options that a user must supply before the image will work with your infrastrucutre. However, unlike using the Ansible-based solution to create your own system, there are far fewer options. Other than the following options, all builds of the Cinch Docker images utilize all default values for a Cinch slave instance.

There are two variables that the user is required to provide before the image will run properly. Those are

Environment Variable	Explanation
JENKINS_MASTER_URL	The URL to the Jenkins master instance that this slave should connect to
JSLAVE_NAME	The name this slave will be given on the Master node
JSLAVE_LABEL	The Jenkins label this slave will receive, which will be matched against jobs requiring certain labels for execution
JSWARM_EXTRA_ARGS	Additional command-line arguments to pass to the JSwarm client in the iamge

If the container image is run directly from the Docker command line, these options may be passed through docker’s -e option. When running the image in Kubernetes or OpenShift, use that system’s methods for passing in environment variables to the iamge.

Customizing the Image

Instead of running the base image provided, a group could choose to use a Dockerfile to extend the base image provided to do such things as install custom software, edit configurations, etc. If that is the case, then the environment variables can absolutely be preset within the Dockerfile using its ENV command, as with any other environment variable.

Extending the image in this way could simplify deployment, as the image could include information such as the Jenkins Master URL already configured to connect to the organization’s Jenkins instance. Likewise, different slave images could be pre-populated with packages and slave labels for building different types of software or running different types of tasks. As nothing more than a standard Docker image, the provided images can be made fully extensible.

One note is that the image is set to run all commands as the user “jenkins”. If the image is being extended, then it might be necessary to set the USER command in the extending Dockerfile to “USER root” if system software is being installed.