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Jenkins-Debian-Glue Docker image

The Jenkins Continuous Integration and Delivery server + jenkins-debian-glue

Based on <a href="https://github.com/cloudbees/jenkins-ci.org-docker">Official Jenkins Docker image</a>

Usage

docker run -p 8080:8080 -p 50000:50000 jenkins

This will store the workspace in /var/jenkins_home. All Jenkins data lives in there - including plugins and configuration.
You will probably want to make that a persistent volume (recommended):

docker run -p 8080:8080 -p 50000:50000 -v /your/home:/var/jenkins_home jenkins

This will store the jenkins data in /your/home on the host.
Ensure that /your/home is accessible by the jenkins user in container (jenkins user - uid 1000) or use -u some_other_user parameter with docker run.

You can also use a volume container:

docker run --name myjenkins -p 8080:8080 -p 50000:50000 -v /var/jenkins_home jenkins

Then myjenkins container has the volume (please do read about docker volume handling to find out more).

Backing up data

If you bind mount in a volume - you can simply back up that directory
(which is jenkins_home) at any time.

This is highly recommended. Treat the jenkins_home directory as you would a database - in Docker you would generally put a database on a volume.

If your volume is inside a container - you can use docker cp $ID:/var/jenkins_home command to extract the data, or other options to find where the volume data is.
Note that some symlinks on some OSes may be converted to copies (this can confuse jenkins with lastStableBuild links etc)

For more info check Docker docs section on Managing data in containers

Setting the number of executors

You can specify and set the number of executors of your Jenkins master instance using a groovy script. By default its set to 2 executors, but you can extend the image and change it to your desired number of executors :

# executors.groovy
Jenkins.instance.setNumExecutors(5)

and Dockerfile

FROM jenkins
COPY executors.groovy /usr/share/jenkins/ref/init.groovy.d/executors.groovy

Attaching build executors

You can run builds on the master (out of the box) but if you want to attach build slave servers: make sure you map the port: -p 50000:50000 - which will be used when you connect a slave agent.

<a href="https://registry.hub.docker.com/u/maestrodev/build-agent/">Here</a> is an example docker container you can use as a build server with lots of good tools installed - which is well worth trying.

Passing JVM parameters

You might need to customize the JVM running Jenkins, typically to pass system properties or tweak heap memory settings. Use JAVA_OPTS environment
variable for this purpose :

docker run --name myjenkins -p 8080:8080 -p 50000:50000 --env JAVA_OPTS=-Dhudson.footerURL=http://mycompany.com jenkins

Passing Jenkins launcher parameters

Argument you pass to docker running the jenkins image are passed to jenkins launcher, so you can run for sample :

docker run jenkins --version

This will dump Jenkins version, just like when you run jenkins as an executable war.

You also can define jenkins arguments as JENKINS_OPTS. This is usefull to define a set of arguments to pass to jenkins launcher as you
define a derived jenkins image based on the official one with some customized settings. The following sample Dockerfile uses this option
to force use of HTTPS with a certificate included in the image

FROM jenkins:1.565.3

COPY https.pem /var/lib/jenkins/cert
COPY https.key /var/lib/jenkins/pk
ENV JENKINS_OPTS --httpPort=-1 --httpsPort=8083 --httpsCertificate=/var/lib/jenkins/cert --httpsPrivateKey=/var/lib/jenkins/pk
EXPOSE 8083

You can also change the default slave agent port for jenkins by defining JENKINS_SLAVE_AGENT_PORT in a sample Dockerfile.

FROM jenkins:1.565.3
ENV JENKINS_SLAVE_AGENT_PORT 50001

or as a parameter to docker,

docker run --name myjenkins -p 8080:8080 -p 50001:50001 --env JENKINS_SLAVE_AGENT_PORT=50001 jenkins

Installing more tools

You can run your container as root - and install via apt-get, install as part of build steps via jenkins tool installers, or you can create your own Dockerfile to customise, for example:

FROM jenkins
# if we want to install via apt
USER root
RUN apt-get update && apt-get install -y ruby make more-thing-here
USER jenkins # drop back to the regular jenkins user - good practice

In such a derived image, you can customize your jenkins instance with hook scripts or additional plugins.
For this purpose, use /usr/share/jenkins/ref as a place to define the default JENKINS_HOME content you
wish the target installation to look like :

FROM jenkins
COPY plugins.txt /usr/share/jenkins/ref/
COPY custom.groovy /usr/share/jenkins/ref/init.groovy.d/custom.groovy
RUN /usr/local/bin/plugins.sh /usr/share/jenkins/ref/plugins.txt

When jenkins container starts, it will check JENKINS_HOME has this reference content, and copy them there if required. It will not override such files, so if you upgraded some plugins from UI they won't be reverted on next start.

Also see JENKINS-24986

For your convenience, you also can use a plain text file to define plugins to be installed (using core-support plugin format)

pluginID:version
anotherPluginID:version

And in derived Dockerfile just invoke the utility plugin.sh script

FROM jenkins
COPY plugins.txt /usr/share/jenkins/plugins.txt
RUN /usr/local/bin/plugins.sh /usr/share/jenkins/plugins.txt

Upgrading

All the data needed is in the /var/jenkins_home directory - so depending on how you manage that - depends on how you upgrade. Generally - you can copy it out - and then "docker pull" the image again - and you will have the latest LTS - you can then start up with -v pointing to that data (/var/jenkins_home) and everything will be as you left it.

As always - please ensure that you know how to drive docker - especially volume handling!

Questions?

Jump on irc.freenode.net and the #jenkins room for jenkins related questions
and #jenkins-debian-glue for questions related to jdg. Enjoy!

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linuxmaniac

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