How to Automate Jenkins Setup with Docker

In the modern software development world, Continuous Integration and Continuous Delivery (CI/CD) have become an integral part of the development process. Jenkins, one of the leading CI/CD tools, helps automate application build, testing, and deployment. However, setting up and managing Jenkins can be time-consuming and complex, especially in large projects with many developers and diverse requirements.

Docker, containerization, and container orchestration have come to the rescue, offering more efficient and scalable solutions for deploying applications and infrastructure. Docker allows developers to package applications and their dependencies into containers, which can be easily transported and run on any system with Docker installed.

Benefits of Using Docker for Automating Jenkins Setup

• Simplified Installation and Setup: Using Docker to deploy Jenkins eliminates many challenges associated with installing dependencies and setting up the environment. You only need to run a few commands to get a fully functional Jenkins server.
• Repeatability: With Docker, you can be confident that your environment will always be the same, regardless of where it runs. This eliminates problems associated with different configurations across different servers.
• Environment Isolation: Docker provides isolation of applications and their dependencies, avoiding conflicts between different projects and services.
• Scalability: Using Docker and orchestration tools such as Docker Compose or Kubernetes allows Jenkins to be easily scaled by adding or removing agents as needed.
• Fast Deployment and Recovery: In case of failure or the need for an upgrade, Docker allows you to quickly deploy a new Jenkins container, minimizing downtime and ensuring business continuity.

In this article, we will discuss how to automate the setup and deployment of Jenkins using Docker. We will cover all the stages, from creating a Docker file and setting up Docker Compose to integrating Jenkins Configuration as Code (JCasC) for automatic Jenkins configuration. As a result, you'll have a complete understanding of the process and a ready-made solution for automating Jenkins in your projects.

Prerequisites

Before you begin setting up Jenkins with Docker, you need to ensure that you have all the necessary tools and software. In this section, we will discuss the requirements for successfully automating Jenkins and how to install the necessary components.

Installing Docker and Docker Compose

Docker can be installed on various operating systems, including Linux, macOS, and Windows. Below are the steps for installing Docker on the most popular platforms:

Linux (Ubuntu)

1. Update the package list with the command:

sudo apt update

2. Install packages for HTTPS support:

sudo apt install apt-transport-https ca-certificates curl software-properties-common

3. Add the official Docker GPG key:

curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -

4. Add the Docker repository to APT sources:

sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"

5. Install Docker:

sudo apt install docker-ce

6. Verify Docker is running:

sudo systemctl status docker

macOS

1. Download and install Docker Desktop from the official website: Docker Desktop for Mac.
2. Follow the on-screen instructions to complete the installation.

Windows

1. Download and install Docker Desktop from the official website: Docker Desktop for Windows.
2. Follow the on-screen instructions to complete the installation.

Docker Compose is typically installed along with Docker Desktop on macOS and Windows. For Linux, it requires separate installation:

1. Download the latest version of Docker Compose:

sudo curl -L "https://github.com/docker/compose/releases/download/$(curl -s https://api.github.com/repos/docker/compose/releases/latest | grep -Po '"tag_name": "\K.*?(?=")')/docker-compose-$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose

2. Make the downloaded file executable:

sudo chmod +x /usr/local/bin/docker-compose

3. Verify the installation:

docker-compose --version

Docker Hub is a cloud-based repository where you can find and store Docker images. The official Jenkins Docker image is available on Docker Hub and provides a ready-to-use Jenkins server.

1. Go to the Docker Hub website.
2. In the search bar, type Jenkins.
3. Select the official image jenkins/jenkins.

The official image is regularly updated and maintained by the community, ensuring a stable and secure environment.

Creating a Dockerfile for Jenkins

In this chapter, we will explore how to create a Dockerfile for Jenkins that will be used to build a Docker image. We will also discuss how to add configurations and plugins to this image to meet the specific requirements of your project.

Structure of a Dockerfile

A Dockerfile is a text document containing all the commands that a user could call on the command line to build an image. In each Dockerfile, instructions are used to define a step in the image-building process. The key commands include:

• FROM: Specifies the base image to create a new image from.
• RUN: Executes a command in the container.
• COPY or ADD: Copies files or directories into the container.
• CMD or ENTRYPOINT: Defines the command that will be executed when the container starts.

Basic Dockerfile for Jenkins

Let’s start by creating a simple Dockerfile for Jenkins. This file will use the official Jenkins image as the base and add a few necessary plugins.

1. Create a new file named Dockerfile in your project directory.
2. Add the following code:

FROM jenkins/jenkins:lts

RUN jenkins-plugin-cli --plugins workflow-aggregator git

EXPOSE 8080
EXPOSE 50000

This basic Dockerfile installs two plugins: workflow-aggregator and git. It also exposes ports 8080 (for the web interface) and 50000 (for connecting Jenkins agents).

Adding Configurations and Plugins

For more complex configurations, we can add additional steps to the Dockerfile. For example, we can configure Jenkins to automatically use a specific configuration file or add scripts for pre-configuration.

1. Create a jenkins_home directory to store custom configurations.

2. Inside the new directory, create a custom_config.xml file with the required configurations:

<?xml version='1.0' encoding='UTF-8'?>
<hudson>
    <numExecutors>2</numExecutors>
    <mode>NORMAL</mode>
    <useSecurity>false</useSecurity>
    <disableRememberMe>false</disableRememberMe>
    <label></label>
    <primaryView>All</primaryView>
    <slaveAgentPort>50000</slaveAgentPort>
    <securityRealm class='hudson.security.SecurityRealm$None'/>
    <authorizationStrategy class='hudson.security.AuthorizationStrategy$Unsecured'/>
</hudson>

3. Update the Dockerfile as follows:

FROM jenkins/jenkins:lts

RUN jenkins-plugin-cli --plugins workflow-aggregator git docker-workflow

COPY jenkins_home/custom_config.xml /var/jenkins_home/config.xml

COPY scripts/init.groovy.d /usr/share/jenkins/ref/init.groovy.d/

EXPOSE 8080
EXPOSE 50000

In this example, we are installing additional plugins, copying the custom configuration file into Jenkins, and adding scripts to the init.groovy.d directory for automatic initialization of Jenkins during its first startup.

Docker Compose Setup

Docker Compose allows you to define your application's infrastructure as code using YAML files. This simplifies the configuration and deployment process, making it repeatable and easier to manage.

Key benefits of using Docker Compose:

• Ease of Use: Create and manage multi-container applications with a single YAML file.
• Scalability: Easily scale services by adding or removing containers as needed.
• Convenience for Testing: Ability to run isolated environments for development and testing.

Example of docker-compose.yml for Jenkins

Let’s create a docker-compose.yml file to deploy Jenkins along with associated services such as a database and Jenkins agent.

1. Create a docker-compose.yml file in your project directory.
2. Add the following code to the file:

version: '3.8'

services:
  jenkins:
    image: jenkins/jenkins:lts
    container_name: jenkins-server
    ports:
      - "8080:8080"
      - "50000:50000"
    volumes:
      - jenkins_home:/var/jenkins_home
    networks:
      - jenkins-network

  jenkins-agent:
    image: jenkins/inbound-agent
    container_name: jenkins-agent
    environment:
      - JENKINS_URL=http://jenkins-server:8080
      - JENKINS_AGENT_NAME=agent
      - JENKINS_AGENT_WORKDIR=/home/jenkins/agent
    volumes:
      - agent_workdir:/home/jenkins/agent
    depends_on:
      - jenkins
    networks:
      - jenkins-network

volumes:
  jenkins_home:
  agent_workdir:

networks:
  jenkins-network:

This file defines two services:

• jenkins: The service uses the official Jenkins image. Ports 8080 and 50000 are forwarded for access to the Jenkins web interface and communication with agents. The /var/jenkins_home directory is mounted on the external volume jenkins_home to persist data across container restarts.
• jenkins-agent: The service uses the Jenkins inbound-agent image. The agent connects to the Jenkins server via the URL specified in the JENKINS_URL environment variable. The agent's working directory is mounted on an external volume agent_workdir.

Once you create the docker-compose.yml file, you can start all services with a single command:

1. Navigate to the directory that contains your docker-compose.yml.
2. Run the following command to start all services:

docker-compose up -d

The -d flag runs the containers in the background. After executing this command, Docker Compose will create and start containers for all services defined in the file.

You can now check the status of the running containers using the following command:

docker-compose ps

If everything went well, you should see only the jenkins-server container in the output.

Now, let’s set up the Jenkins server and agent.

1. Open a browser and go to http://localhost:8080/. During the first startup, you will see the following message:

To retrieve the password, run this command:

docker exec -it jenkins-server cat /var/jenkins_home/secrets/initialAdminPassword

2. Copy the password and paste it into the Unlock Jenkins form. This will open a new window with the initial setup.

3. Select Install suggested plugins. After the installation is complete, fill out the form to create an admin user.

4. Accept the default URL and finish the setup. Then, go to Manage Jenkins → Manage Nodes.

5. Click New Node, provide a name for the new node (e.g., "agent"), and select Permanent Agent. Fill in the remaining fields as shown in the screenshot.

After creating the agent, a window will open with a command containing the secret for the agent connection.

6. Copy the secret and add it to your docker-compose.yml:

environment:
  - JENKINS_URL=http://jenkins-server:8080
  - JENKINS_AGENT_NAME=agent
  - JENKINS_AGENT_WORKDIR=/home/jenkins/agent
  - JENKINS_SECRET=<your-secret-here>  # Insert the secret here

To restart the services, use the following commands and verify that the jenkins-agent container has started:

docker-compose down
docker-compose up -d

Configuring Jenkins with Code (JCasC)

Jenkins Configuration as Code (JCasC) is an approach that allows you to describe the entire Jenkins configuration in a YAML file. It simplifies the automation, maintenance, and portability of Jenkins settings. In this chapter, we will explore how to set up JCasC for automatic Jenkins configuration when the container starts.

JCasC allows you to describe Jenkins configuration in a single YAML file, which provides the following benefits:

• Automation: A fully automated Jenkins setup process, eliminating the need for manual configuration.
• Manageability: Easier management of configurations using version control systems.
• Documentation: Clear and easily readable documentation of Jenkins configuration.

Example of a Jenkins Configuration File

First, create the configuration file.

1. Create a file named jenkins.yaml in your project directory.

2. Add the following configuration to the file:

jenkins:
  systemMessage: "Welcome to Jenkins configured as code!"
  securityRealm:
    local:
      allowsSignup: false
      users:
        - id: "admin"
          password: "${JENKINS_ADMIN_PASSWORD}"
  authorizationStrategy:
    loggedInUsersCanDoAnything:
      allowAnonymousRead: false
  tools:
    jdk:
      installations:
        - name: "OpenJDK 11"
          home: "/usr/lib/jvm/java-11-openjdk"
  jobs:
    - script: >
        pipeline {
          agent any
          stages {
            stage('Build') {
              steps {
                echo 'Building...'
              }
            }
            stage('Test') {
              steps {
                echo 'Testing...'
              }
            }
            stage('Deploy') {
              steps {
                echo 'Deploying...'
              }
            }
          }
        }

This configuration file defines:

• System message in the systemMessage block. This string will appear on the Jenkins homepage and can be used to inform users of important information or changes.

• Local user database and administrator account in the securityRealm block. The field allowsSignup: false disables self-registration of new users. Then, a user with the ID admin is defined, with the password set by the environment variable ${JENKINS_ADMIN_PASSWORD}.

• Authorization strategy in the authorizationStrategy block. The policy loggedInUsersCanDoAnything allows authenticated users to perform any action, while allowAnonymousRead: false prevents anonymous users from accessing the system.

• JDK installation in the tools block. In this example, a JDK named OpenJDK 11 is specified with the location /usr/lib/jvm/java-11-openjdk.

• Pipeline example in the jobs block. This pipeline includes three stages: Build, Test, and Deploy, each containing one step that outputs a corresponding message to the console.

Integrating JCasC with Docker and Docker Compose

Next, we need to integrate our jenkins.yaml configuration file with Docker and Docker Compose so that this configuration is automatically applied when the Jenkins container starts.

1. Update the Dockerfile to copy the configuration file into the container and install the JCasC plugin:

FROM jenkins/jenkins:lts

RUN jenkins-plugin-cli --plugins configuration-as-code

COPY jenkins.yaml /var/jenkins_home/jenkins.yaml

EXPOSE 8080
EXPOSE 50000

2. Update the docker-compose.yml to set environment variables and mount the configuration file. Add the following code in the volumes block:

- ./jenkins.yaml:/var/jenkins_home/jenkins.yaml

After the volumes block, add a new environment block (if you haven't defined it earlier):

environment:
 - JENKINS_ADMIN_PASSWORD=admin_password

3. Build the new Jenkins image with the JCasC configuration:

docker-compose build

4. Run the containers:

docker-compose up -d

After the containers start, go to your browser at http://localhost:8080 and log in with the administrator account. You should see the system message and the Jenkins configuration applied according to your jenkins.yaml file.

A few important notes:

• The YAML files docker-compose.yml and jenkins.yaml might seem similar at first glance but serve completely different purposes. The file in Docker Compose describes the services and containers needed to run Jenkins and its environment, while the file in JCasC describes the Jenkins configuration itself, including plugin installation, user settings, security, system settings, and jobs.

• The .yml and .yaml extensions are variations of the same YAML file format. They are interchangeable and supported by various tools and libraries for working with YAML. The choice of format depends largely on historical community preferences; in Docker documentation, you will more often encounter examples with the .yml extension, while in JCasC documentation, .yaml is more common.

• The pipeline example provided below only outputs messages at each stage with no useful payload. This example is for demonstrating structure and basic concepts, but it does not prevent Jenkins from successfully applying the configuration. We will not dive into more complex and practical structures. jenkins.yaml describes the static configuration and is not intended to define the details of a specific CI/CD process for a particular project. For that purpose, you can use the Jenkinsfile, which offers flexibility for defining specific CI/CD steps and integrating with version control systems. We will discuss this in more detail in the next chapter.

Key Concepts of Jobs in JCasC

Jobs are a section of the configuration file that allows you to define and configure build tasks using code. This block includes the following:

• Description of Build Tasks: This section describes all aspects of a job, including its type, stages, triggers, and execution steps.
• Types of Jobs: There are different types of jobs in Jenkins, such as freestyle projects, pipelines, and multiconfiguration projects. In JCasC, pipelines are typically used because they provide a more flexible and powerful approach to automation.
• Declarative Syntax: Pipelines are usually described using declarative syntax, simplifying understanding and editing.

Example Breakdown:

• pipeline: The main block that defines the pipeline job.

• agent any: Specifies that the pipeline can run on any available Jenkins agent.

• stages: The block that contains the pipeline stages. A stage is a step in the process.

Additional Features:

• Triggers: You can add triggers to make the job run automatically under certain conditions, such as on a schedule or when a commit is made to a repository:

triggers {
    cron('H 4/* 0 0 1-5')
}

• Post-Conditions: You can add post-conditions to execute steps after the pipeline finishes, such as sending notifications or archiving artifacts.

• Parameters: You can define parameters for a job to make it configurable at runtime:

parameters {
    string(name: 'BRANCH_NAME', defaultValue: 'main', description: 'Branch to build')
}

Automating Jenkins Deployment in Docker with JCasC

Using Scripts for Automatic Deployment

• Use Bash scripts to automate the installation, updating, and running Jenkins containers.
• Leverage Jenkins Configuration as Code (JCasC) to automate Jenkins configuration.

Script Examples

Script for Deploying Jenkins in Docker:

#!/bin/bash

# Jenkins Parameters
JENKINS_IMAGE="jenkins/jenkins:lts"
CONTAINER_NAME="jenkins-server"
JENKINS_PORT="8080"
JENKINS_AGENT_PORT="50000"
VOLUME_NAME="jenkins_home"
CONFIG_DIR="$(pwd)/jenkins_configuration"

# Create a volume to store Jenkins data
docker volume create $VOLUME_NAME

# Run Jenkins container with JCasC
docker run -d \
    --name $CONTAINER_NAME \
    -p $JENKINS_PORT:8080 \
    -p $JENKINS_AGENT_PORT:50000 \
    -v $VOLUME_NAME:/var/jenkins_home \
    -v $CONFIG_DIR:/var/jenkins_home/casc_configs \
    -e CASC_JENKINS_CONFIG=/var/jenkins_home/casc_configs \
    $JENKINS_IMAGE

The JCasC configuration file jenkins.yaml was discussed earlier.

Setting Up a CI/CD Pipeline for Jenkins Updates

To set up a CI/CD pipeline, follow these steps:

1. Open Jenkins and go to the home page.

2. Click on Create Item.

3. Enter a name for the new item, select Pipeline, and click OK.

4. If this section is missing, you need to install the plugin in Jenkins. Go to Manage Jenkins → Manage Plugins. In the Available Plugins tab, search for Pipeline and install the Pipeline plugin.

5. Similarly, install the Git Push plugin.

5. After installation, go back to Create Item.

6. Select Pipeline, and under Definition, choose Pipeline script from SCM. Select Git as the SCM.

7. Add the URL of your repository; if it's private, add the credentials. In the Branch Specifier field, specify the branch that contains the Jenkinsfile (e.g., */main). Note that the Jenkinsfile should be created without an extension. If it's located in a subdirectory, specify it in the Script Path field.

8. Click Save.

Example of a Jenkinsfile

pipeline {
    agent any

    environment {
        JENKINS_CONTAINER_NAME = 'new-jenkins-server'
        JENKINS_IMAGE = 'jenkins/jenkins:lts'
        JENKINS_PORT = '8080'
        JENKINS_VOLUME = 'jenkins_home'
    }

    stages {
        stage('Setup Docker') {
            steps {
                script {
                    // Install Docker on the server if it's not installed
                    sh '''
                    if ! [ -x "$(command -v docker)" ]; then
                      curl -fsSL https://get.docker.com -o get-docker.sh
                      sh get-docker.sh
                    fi
                    '''
                }
            }
        }
        stage('Pull Jenkins Docker Image') {
            steps {
                script {
                    // Pull the latest Jenkins image
                    sh "docker pull ${JENKINS_IMAGE}"
                }
            }
        }
        stage('Cleanup Old Jenkins Container') {
            steps {
                script {
                    // Stop and remove the old container if it exists
                    def existingContainer = sh(script: "docker ps -a -q -f name=${JENKINS_CONTAINER_NAME}", returnStdout: true).trim()
                    
                    if (existingContainer) {
                        echo "Stopping and removing existing container ${JENKINS_CONTAINER_NAME}..."
                        sh "docker stop ${existingContainer} || true"
                        sh "docker rm -f ${existingContainer} || true"
                    } else {
                        echo "No existing container with name ${JENKINS_CONTAINER_NAME} found."
                    }
                }
            }
        }
        stage('Run Jenkins Container') {
            steps {
                script {
                    // Run Jenkins container with port binding and volume mounting
                    sh '''
                    docker run -d --name ${JENKINS_CONTAINER_NAME} \
                      -p ${JENKINS_PORT}:8080 \
                      -p 50000:50000 \
                      -v ${JENKINS_VOLUME}:/var/jenkins_home \
                      ${JENKINS_IMAGE}
                    '''
                }
            }
        }
        stage('Configure Jenkins (Optional)') {
            steps {
                script {
                    // Additional Jenkins configuration through Groovy scripts or REST API
                    sh '''
                    # Example script for performing initial Jenkins setup
                    curl -X POST http://localhost:${JENKINS_PORT}/scriptText --data-urlencode 'script=println("Jenkins is running!")'
                    '''
                }
            }
        }
    }

    post {
        always {
            echo "Jenkins setup and deployment process completed."
        }
    }
}

9. On the page of your new pipeline, click Build Now.

10. Go to Console Output. In case of a successful completion, you should see the following output.

For this pipeline, we used the following files. 

Dockerfile:

FROM jenkins/jenkins:lts

USER root
RUN apt-get update && apt-get install -y docker.io

docker-compose.yml:

version: '3.7'

services:
  jenkins:
    build: .
    ports:
      - "8081:8080" 
      - "50001:50000"
    volumes:
      - jenkins_home:/var/jenkins_home
      - /var/run/docker.sock:/var/run/docker.sock
    environment:
      - JAVA_OPTS=-Djenkins.install.runSetupWizard=false
    networks:
      - jenkins-network

volumes:
  jenkins_home:

networks:
  jenkins-network:

Ports 8081 and 50001 are used here so that the newly deployed Jenkins can occupy ports 8080 and 50000, respectively. This means that the main Jenkins, from which the pipeline is running, is currently located at http://localhost:8081/. One way to check if Jenkins has been deployed is to go to http://localhost:8080/, as we specified this in the pipeline. Since this is a new image, a welcome message with authentication will appear on the homepage.

Conclusion

Automating the deployment, updates, and backups of Jenkins is crucial for ensuring the reliability and security of CI/CD processes. Using modern tools enhances this process with a variety of useful features and resources.

If you're further interested in exploring Jenkins capabilities, we recommend the following useful resources that can assist with automating deployments:

• Official Jenkins website
• Jenkins Configuration as Code documentation
• Pipeline Syntax