Adding an SSH Based Agent to Jenkins

Prerequsites

• Virtual Machine running Ubuntu 22.04 or newer

Update Package Repository and Upgrade Packages

sudo apt update
sudo apt upgrade

Create Jenkins User

sudo adduser jenkins

Grant Sudo Rights to Jenkins User

sudo usermod -aG sudo jenkins

Logout and ssh back as user Jenkins

Adoptium Java 11

sudo bash

Add Adoptium repository

wget -O - https://packages.adoptium.net/artifactory/api/gpg/key/public | tee /etc/apt/keyrings/adoptium.asc
echo "deb [signed-by=/etc/apt/keyrings/adoptium.asc] https://packages.adoptium.net/artifactory/deb $(awk -F= '/^VERSION_CODENAME/{print$2}' /etc/os-release) main" | tee /etc/apt/sources.list.d/adoptium.list

Install Java 11

apt update
apt install temurin-11-jdk
update-alternatives --config java
/usr/bin/java --version
exit 

Docker

Install using the repository

Update the apt package index and install packages to allow apt to use a repository over HTTPS:

sudo apt-get update

sudo apt-get install \
    ca-certificates \
    curl \
    gnupg \
    lsb-release

Add Docker’s official GPG key:

sudo mkdir -m 0755 -p /etc/apt/keyrings
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg

Use the following command to set up the repository:

echo \
  "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu \
  $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

Install Docker Engine

sudo apt-get update
sudo apt-get install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

Manage Docker as a non-root user

Create the docker group.

sudo groupadd docker

Add your user to the docker group.

sudo usermod -aG docker $USER

Run the following command to activate the changes to groups:

newgrp docker

Verify that you can run docker commands without sudo.

docker run hello-world

Connect to Remote SSH Agent

From the Jenkins UI (Controller)

ssh jenkins@$AGENT_HOSTNAME

Create private and public SSH keys. The following command creates the private key jenkinsAgent_rsa and the public key jenkinsAgent_rsa.pub. It is recommended to store your keys under ~/.ssh/ so we move to that directory before creating the key pair.

 mkdir ~/.ssh; cd ~/.ssh/ && ssh-keygen -t rsa -m PEM -C "Jenkins agent key" -f "jenkinsAgent_rsa"

Add the public SSH key to the list of authorized keys on the agent machine

cat jenkinsAgent_rsa.pub >> ~/.ssh/authorized_keys

Ensure that the permissions of the ~/.ssh directory is secure, as most ssh daemons will refuse to use keys that have file permissions that are considered insecure:

chmod 700 ~/.ssh
 chmod 600 ~/.ssh/authorized_keys ~/.ssh/jenkinsAgent_rsa

Copy the private SSH key (~/.ssh/jenkinsAgent_rsa) from the agent machine to your OS clipboard

cat ~/.ssh/jenkinsAgent_rsa

Now you can add the Agent on the Jenkins UI (Controller)