How To Automate Jenkins Setup with Docker and Jenkins Configuration as Code

Jenkins uses a pluggable architecture to provide most of its functionality. JCasC makes use of the Configuration as Code plugin, which allows you to define the desired state of your Jenkins configuration as one or more YAML file(s), eliminating the ne

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Introduction

Jenkins is one of the most popular open-source automation servers, often used to orchestrate continuous integration (CI) and/or continuous deployment (CD) workflows.

Configuring Jenkins is typically done manually through a web-based setup wizard; this can be a slow, error-prone, and non-scalable process. You can see the steps involved by following Step 4 — Setting Up Jenkins of the How To Install Jenkins on Ubuntu 18.04 guide. Furthermore, configurations cannot be tracked in a version control system (VCS) like Git, nor be under the scrutiny of any code review process.

In this tutorial, you will automate the installation and configuration of Jenkins using Docker and the Jenkins Configuration as Code (JCasC) method.

Jenkins uses a pluggable architecture to provide most of its functionality. JCasC makes use of the Configuration as Code plugin, which allows you to define the desired state of your Jenkins configuration as one or more YAML file(s), eliminating the need for the setup wizard. On initialization, the Configuration as Code plugin would configure Jenkins according to the configuration file(s), greatly reducing the configuration time and eliminating human errors.

Docker is the de facto standard for creating and running containers, which is a virtualization technology that allows you to run isolated, self-contained applications consistently across different operation systems (OSes) and hardware architectures. You will run your Jenkins instance using Docker to take advantage of this consistency and cross-platform capability.

This tutorial starts by guiding you through setting up JCasC. You will then incrementally add to the JCasC configuration file to set up users, configuration authentication and authorization, and finally to secure your Jenkins instance. After you’ve completed this tutorial, you’ll have created a custom Docker image that is set up to use the Configuration as Code plugin on startup to automatically configure and secure your Jenkins instance.

Prerequisites

To complete this tutorial, you will need:

• Access to a server with at least 2GB of RAM and Docker installed. This can be your local development machine, a Droplet, or any kind of server. Follow Step 1 — Installing Docker from one of the tutorials in the How to Install and Use Docker collection to set up Docker.

Note:  This tutorial is tested on Ubuntu 18.04; however, because Docker images are self-contained, the steps outlined here would work for any OSes with Docker installed.

Step 1 — Disabling the Setup Wizard

Using JCasC eliminates the need to show the setup wizard; therefore, in this first step, you’ll create a modified version of the official [jenkins/jenkins](https://hub.docker.com/r/jenkins/jenkins/) image that has the setup wizard disabled. You will do this by creating a Dockerfile and building a custom Jenkins image from it.

The jenkins/jenkins image allows you to enable or disable the setup wizard by passing in a system property named jenkins.install.runSetupWizard via the JAVA_OPTS environment variable. Users of the image can pass in the JAVA_OPTS environment variable at runtime using the [--env](https://docs.docker.com/engine/reference/commandline/run/#set-environment-variables--e---env---env-file) flag to docker run. However, this approach would put the onus of disabling the setup wizard on the user of the image. Instead, you should disable the setup wizard at build time, so that the setup wizard is disabled by default.

You can achieve this by creating a Dockerfile and using the [ENV](https://docs.docker.com/engine/reference/builder/#env) instruction to set the JAVA_OPTS environment variable.

First, create a new directory inside your server to store the files you will be creating in this tutorial:

mkdir -p $HOME/playground/jcasc

Then, navigate inside that directory:

cd $HOME/playground/jcasc

Next, using your editor, create a new file named Dockerfile:

nano $HOME/playground/jcasc/Dockerfile

Then, copy the following content into the Dockerfile:

~/playground/jcasc/

FROM jenkins/jenkins:latest
ENV JAVA_OPTS -Djenkins.install.runSetupWizard=false

Here, you’re using the [FROM](https://docs.docker.com/engine/reference/builder/#from) instruction to specify jenkins/jenkins:latest as the base image, and the ENV instruction to set the JAVA_OPTS environment variable.

Save the file and exit the editor by pressing CTRL+X followed by Y.

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