Jenkins with Docker

What is this?

This is a Dockerfile and set of helper scripts to get Jenkins CI server up and running with proper permissions to the host /var/run/docker.sock. The dreaded and common permission denied problem is solved with a properly built container using this repo. Everything is optimised for use on your local workstation with a minimum of hassle (and security!), and not recommended for use in a team setting. If the latter is what you're after, just fork and refer to the article referenced at the end of this README.

With a Jenkins container built from this repo, you can easily use Docker images as an execution environment in your Pipelines. For example:

pipeline {
    agent {
        docker { image 'node:alpine' }
    }
    stages {
        stage('Test') {
            steps {
                sh 'node --version'
            }
        }
    }
}

This allows you to use any Docker container for build steps or pipelines without needing to install dependencies on your workstation or in a custom Jenkins image.

What does "minimum of hassle (and security)" mean?

It means:

• The Jenkins setup wizard is skipped.
• NO SECURITY IS ENABLED! ALL ACCESS IS ANONYMOUS! Great for use on your local workstation, but NOT suitable if you want to expose this to a LAN or WAN.
• A common set of plugins is installed by default, but you can easily customise them by editing config/plugins.txt.
• The Code as Configuration plugin is enabled and a customisable basic config is provided.
• HTTP (not HTTPS).

How to use this repo

1. Clone the repo.
2. Edit env_vars.sh to your liking. SUPER IMPORTANT: MAKE SURE YOU SET THE UID AND GID AS THE COMMENTS INSTRUCT! If you don't do this, Jenkins will almost certainly not be able to access /var/run/docker.sock and you'll get permission denied errors.

#
# SUPER IMPORTANT!
#   HOST_DOCKER_UID: UID of user in docker group *ON THE HOST* 
#   HOST_DOCKER_GID: GID of docker group *ON THE HOST*
#
# To find these values, use the id command on the host
#  (as a user that's been added to the docker group). E.g.:
#   rocket@ubuntu:~$ id
#   uid=1000(rocket) groups=1000(rocket),1001(docker)
#
HOST_DOCKER_UID=1000
HOST_DOCKER_GID=1001

3. Run build_and start_jenkins.sh. You only need to run this script once. It builds the image and creates a container with a persistent volume for JENKINS_HOME. So, if you stop the container, you only need to docker start jenkins-docker (or whatever you set CONTAINER_NAME to before running the script) to start it again.

$ sh ./build_and start_jenkins.sh

4. Access the Jenkins UI at http://locahost:8080 (unless you changed the vars in env_vars.sh ... read on ...)

How do I tweak stuff?

After the first run of build_and start_jenkins.sh, a persistent volume is created for the Jenkins home dir (where all build and job config data is stored). So, to add or delete plugins or change any other config, you can use the Jenkins UI as normal. Any changes you make will be persisted across restarts of the container. However, if you ever delete the volume, all your changes will be lost (along with any jobs and builds).

If you want to bake changes into the image, just run cleanup_jenkins.sh to stop and remove the container. Then, hack away; the scripts are fairly-well commented. To change the list of default plugins, simply edit config/plugins.txt and rebuild the image.

Prerequisites

Ensure you've got a recent (18.09+) Docker Desktop or Docker Engine installation.

Troubleshooting

The most likely thing to go wrong is that Jenkins will get a permission denied error while trying to access /var/run/docker.sock. Follow the instructions above in step #2 carefully.

Credit and next steps

Most of this repo comes from the article at https://www.digitalocean.com/community/tutorials/how-to-automate-jenkins-setup-with-docker-and-jenkins-configuration-as-code. Read the article if you want to learn how to automate a user and build credentials to further secure your container.