Jenkins With Docker Agents

🔥 Adding Docker-Based Jenkins Agents

To add Jenkins agents running as Docker containers, you need to: 1️⃣ Install Docker in the Jenkins controller container. 2️⃣ Install and configure the “Docker Plugin” in Jenkins. 3️⃣ Configure Jenkins to launch Docker-based agents dynamically. 🚀 Step 1: Run Jenkins with Docker Access

First, ensure your Jenkins container can communicate with the Docker daemon. Run Jenkins with the Docker socket mounted:

docker run -d \
  -p 8080:8080 \
  -p 50000:50000 \
  --name jenkins \
  --user root \
  -v jenkins_home:/var/jenkins_home \
  -v /var/run/docker.sock:/var/run/docker.sock \
  jenkins/jenkins:lts

Now, install Docker inside the Jenkins container:

docker exec -it jenkins bash
apt-get update && apt-get install -y docker.io
exit

🔧 Step 2: Install the Docker Plugin in Jenkins

Open Jenkins at http://your-server-ip:8080/

• Go to Manage Jenkins → Manage Plugins
• In the “Available” tab, search for “Docker Plugin” and install it.
• Restart Jenkins after installation.

⚙️ Step 3: Configure Docker Cloud in Jenkins

Go to Manage Jenkins → Manage Nodes and Clouds → Configure Clouds
Click Add a new cloud → Select Docker
In "Docker Host URI", enter:

unix:///var/run/docker.sock

Click Test Connection → It should be successful.

🏗 Step 4: Create a Docker Agent Template

Under "Docker Agent templates," click Add Docker Template
Set:
    Label: docker-agent
    Docker Image: Use jenkins/inbound-agent (official Jenkins agent)
    Remote File System Root: /home/jenkins
    Usage: "Use this node as much as possible"
    Launch Method: Select "Attach Docker container"
Click Save.

✅ Step 5: Run a Test Pipeline Using Docker Agents

Now create a simple Jenkins Pipeline:

Go to Jenkins Dashboard → New Item → Pipeline Use the following script:

pipeline {
    agent { label 'docker-agent' }
    stages {
        stage('Run on Docker Agent') {
            steps {
                sh 'echo "Running on a Docker Agent!"'
                sh 'docker --version'
            }
        }
    }
}

Click Build Now → Jenkins will automatically start a Docker agent and run the job inside it.

🎯 Final Notes

• Dynamic Agents: Jenkins will only spin up agents when needed and remove them after execution.
• If agents don’t start: Check Manage Nodes and Clouds → Check agent logs.
• Using Custom Images: You can specify a different agent image, e.g., python:3.10, maven:latest, etc.

---

Let me know if you need more details! 🚀

It looks like Jenkins inside your container does not have the Docker CLI installed. Mounting the Docker socket (/var/run/docker.sock) allows the container to communicate with the Docker daemon running on your host, but the Jenkins container itself still needs the docker CLI to execute commands. Solution: Use a Docker-in-Docker (DinD) Approach

Instead of using the basic jenkins/jenkins image, use jenkins/jenkins:lts with Docker installed or use a dedicated image like jenkins/jenkins:lts-jdk17 that comes with Docker.

Steps to Fix

1️⃣ Run Jenkins with Docker Installed

Instead of jenkins/jenkins:latest, use jenkins/jenkins:lts and manually install Docker inside it.

docker run -d \
  -p 8080:8080 \
  -p 50000:50000 \
  --name jenkins \
  --user root \
  -v jenkins_home:/var/jenkins_home \
  -v /var/run/docker.sock:/var/run/docker.sock \
  jenkins/jenkins:lts

2️⃣ Install Docker in the Jenkins Container

Once the container is running, enter it:

docker exec -it jenkins bash

Then, install Docker inside the Jenkins container:

apt-get update && apt-get install -y docker.io

3️⃣ Verify Docker Inside Jenkins

Run inside the container:

docker --version
docker ps

If these commands work, your Jenkins pipelines should now be able to execute docker commands successfully. Alternative: Use the jenkinsci/blueocean Image

The jenkinsci/blueocean image comes pre-installed with Docker CLI:

docker run -d \
  -p 8080:8080 \
  -p 50000:50000 \
  --name jenkins \
  --user root \
  -v jenkins_home:/var/jenkins_home \
  -v /var/run/docker.sock:/var/run/docker.sock \
  jenkinsci/blueocean
 

This might be an easier way if you don’t want to manually install Docker inside Jenkins.

Let me know if you need more help! 🚀 You said: why -p 50000:50000 \ ChatGPT said: ChatGPT

The -p 50000:50000 option in your Docker run command is used to expose the Jenkins agent (slave) communication port. 🔹 Why is Port 50000 Used?

Jenkins uses port 50000 for JNLP-based (Java Network Launch Protocol) agent communication. This is needed when Jenkins connects to remote build agents (worker nodes) that run jobs.

• If you plan to run Jenkins agents on different machines and connect them to your Jenkins controller, you should expose port 50000.
• If you are running everything on a single container without agents, you don’t need -p 50000:50000.

✅ When to Use -p 50000:50000

✔️ If you want to add remote Jenkins agents. ✔️ If you use JNLP (Java Web Start) agents to connect workers to Jenkins. ❌ When You Can Skip It

❌ If you are running all jobs inside the Jenkins container itself. ❌ If you are using Docker-based agents instead of traditional JNLP agents. 🛠 Example Without Agents (If You Don’t Need Port 50000)

docker run -d \
  -p 8080:8080 \
  --name jenkins \
  --user root \
  -v jenkins_home:/var/jenkins_home \
  -v /var/run/docker.sock:/var/run/docker.sock \
  jenkins/jenkins:lts