Jenkins Node Addition

Jenkins Node Addition and Configuration Guide

This guide describes how to add and configure a new Jenkins node, install Java 11 on it, configure SSH keys, and connect it successfully to the Jenkins master.

1. Install Java 11 on the New Node

On the new Jenkins node server, install Java 11 (required for Jenkins agents to run).

Example (Debian/Ubuntu):

apt update
apt install openjdk-11-jdk -y

Verify installation:

java -version

2. Configure SSH Keys for Jenkins Connection

Jenkins communicates with the node over SSH. We use the Jenkins master’s SSH key to connect to the node.

Step 2.1: Locate the Jenkins Master SSH Key

On the Jenkins master server, the SSH key pair for Jenkins is typically stored in:

/var/lib/jenkins/.ssh/id_rsa   (private key)
/var/lib/jenkins/.ssh/id_rsa.pub   (public key)

Step 2.2: Add Jenkins Master Public Key to Node

On the node server, add the Jenkins master’s public key to:

/var/lib/jenkins/.ssh/authorized_keys

Ensure correct permissions:

chmod 700 /var/lib/jenkins/.ssh
chmod 600 /var/lib/jenkins/.ssh/authorized_keys
chown -R jenkins:jenkins /var/lib/jenkins/.ssh

3. Add Jenkins Node in Jenkins UI

1. Open Jenkins master web UI. 2. Go to **Manage Jenkins → Nodes → New Node**. 3. Enter the node name (e.g., ci-node). 4. Select "Permanent Agent". 5. Configure:

  - Remote root directory: `/var/lib/jenkins`
  - Number of executors: `2`
  - Labels: `ci-node`
  - Launch method: "Launch agents via SSH"

4. Configure Node SSH Credentials

1. In Jenkins, go to **Manage Jenkins → Credentials → (Global)**. 2. Add new credentials:

  - Kind: SSH Username with private key
  - Username: jenkins
  - Private key: Enter directly → paste contents of:
    /var/lib/jenkins/.ssh/id_rsa  (from Jenkins master)

3. Save credentials.

5. Link Node with Credentials

In the node configuration page: 1. Set the host to the node's IP address. 2. Select the SSH credentials saved earlier. 3. Save the node configuration.

6. Update /etc/hosts (If Required)

If the node or deployment server requires name resolution, update the `/etc/hosts` file on both servers to map hostnames to IPs.

Example:

192.168.1.100   ci-node

7. Permissions on Node

Ensure that the Jenkins user on the node has: - Access to `/var/lib/jenkins` - Proper ownership and permissions for SSH files - Ability to run Java 11

8. Verify Connection

After saving the configuration, Jenkins will attempt to connect to the node: - Logs will display Java startup commands - If successful, status will show "Agent connected"

Final Result

Once connected, the node will be available for Jenkins builds and deployments. You can now assign jobs to run on this node by using the label: ci-node