Docker-in-Docker considerations in Jenkins - Mini Project: Build & Apply

Docker-in-Docker Considerations with Jenkins

📖 Scenario: You are setting up a Jenkins pipeline that needs to build Docker images inside a Jenkins container. This requires understanding how to configure Docker-in-Docker (DinD) safely and correctly.

🎯 Goal: Build a Jenkins pipeline script that sets up Docker-in-Docker by defining the Docker daemon socket path, configuring the Docker image, and running a Docker build command inside the pipeline.

📋 What You'll Learn

Create a Jenkins pipeline variable for the Docker socket path

Configure the Docker agent to use the Docker-in-Docker image

Write a pipeline stage that runs a Docker build command using the socket

Print the Docker image build output

💡 Why This Matters

🌍 Real World

Many CI/CD pipelines need to build Docker images inside containers. Docker-in-Docker allows Jenkins to run Docker commands safely inside its own container.

💼 Career

Understanding Docker-in-Docker is essential for DevOps engineers working with containerized build pipelines and automating Docker image builds in Jenkins.

1

Set Docker socket path variable

Create a pipeline variable called dockerSocket and set it to "/var/run/docker.sock".

Jenkins

# Create a variable called dockerSocket and set it to "/var/run/docker.sock"
# Your code here

Need a hint?

The Docker socket path is usually /var/run/docker.sock. Assign it to a variable named dockerSocket.

2

Configure Docker agent with DinD image

Add an agent block to the pipeline that uses the Docker image docker:20.10.16-dind and mounts the Docker socket using dockerSocket as the volume path.

Jenkins

def dockerSocket = "/var/run/docker.sock"
// Add an agent block using docker:20.10.16-dind image and mount dockerSocket as volume
# Your code here

Need a hint?

Use the docker agent with image set to docker:20.10.16-dind. Use args to mount the socket volume with -v ${dockerSocket}:${dockerSocket}.

3

Add a build stage with Docker build command

Inside the pipeline block, add a stage named Build Image that runs the shell command docker build -t myapp:latest . using the sh step.

Jenkins

def dockerSocket = "/var/run/docker.sock"
pipeline {
    agent {
        docker {
            image 'docker:20.10.16-dind'
            args "-v ${dockerSocket}:${dockerSocket}"
        }
    }
    // Add a stage named 'Build Image' that runs 'docker build -t myapp:latest .'
    // Use the sh step
    # Your code here
}

Need a hint?

Inside stages, add a stage named Build Image. Use steps with sh 'docker build -t myapp:latest .' to build the Docker image.

4

Print Docker build output

Add a post block inside the Build Image stage that prints "Docker build completed successfully" using the echo step when the build succeeds.

Jenkins

def dockerSocket = "/var/run/docker.sock"
pipeline {
    agent {
        docker {
            image 'docker:20.10.16-dind'
            args "-v ${dockerSocket}:${dockerSocket}"
        }
    }
    stages {
        stage('Build Image') {
            steps {
                sh 'docker build -t myapp:latest .'
            }
            // Add a post block that echoes success message on build success
            # Your code here
        }
    }
}

Need a hint?

Use a post block inside the stage with a success condition. Inside it, use echo to print the message.