CINQby Victor Louisa
While developing my Jenkinsfile and init Groovy scripts, I needed a Jenkins Docker image that I could launch and destroy easily with a minimal amount of manual interaction. To my surprise, I needed to google multiple references to set this up. Enough reason for me to share my findings and results.
Jenkins offers an official Docker image jenkins/jenkins. This is a good starting point to create your own image since it contains an extensive readme with all kinds of code snippets that you can use in your Dockerfile.
Browse to http://localhost:80 and you immediately see some manual steps which are nice for a first Jenkins experience, but not in your development environment.
You need to:
– Copy a secret key from the log file,
– Select plugins
– Login with a default username/password
– Create a project
So this gives us four manual steps we want to get rid off. To do this, we will create a Dockerfile and some initial Groovy script to configure Jenkins during start up.
We start our Dockerfile by extending the Jenkins image as described in the readme ot the jenkins/jenkins image.
After each step, we will need to build and run our new image so we can verify the result.
The first step to take is to disable the welcome page called “SetupWizard” where you need to add a secret key. This can be done by adding a Java option to your Dockerfile.
As a second step we don’t want to login upon each restart, so we need to remove the required default credentials. This is done with a small Groovy script which can be added to the init.groovy.d directory. All Groovy files in this directory will be executed during startup.
Created the file: init.groovy.d/disable-securit.groovy
And put the whole init.groovy.d directory in your image using COPY in the Dockerfile:
The --chown=jenkins:jenkins option is added here to resolve permission problems.
Plugins can be installed easily by giving the plugin ID to the install-plugins.sh script. This script is provided in the official Jenkins image. I have listed some useful plugins here which we add to our Dockerfile.
During startup I want Jenkins to load my Git repository containing the Jenkinsfile. This can be done by adding another Groovy script initial_project.groovy to the init.groovy.d directory. I have added a Hello World Jenkinsfile example to the repository so we let Jenkins search in https://github.com/cinqict/jenkinsdev.
Note: We have already copied the init.groovy.d directory in our Dockerfile. So when you rebuild and start the image, Jenkins will start with my new project.
Both the list of plugins and the init.groovy.d scripts will change from time to time. Following the Docker best practices , we should put them at the end of my Dockerfile. Since downloading the plugins takes the biggest amount of time, we only want to do this if it’s really necessary. So it is best to put the plugins above the init.groovy.d scripts. We end up with the following Dockerfile:
These Dockerfile and init Groovy scripts give a simple Jenkins image which you can run en destroy in seconds and is therefore very useful for developing Jenkinsfiles and init Groovy scripts.
All code can be found on https://github.com/cinqict/jenkinsdev