Jenkins Master (Server)

Jenkins’s server or master node holds all key configurations. Jenkins master server is like a control server that orchestrates all the workflow defined in the pipelines. For example, scheduling a job, monitoring the jobs, etc.

Jenkins Agent

An agent is typically a machine or container that connects to a Jenkins master and this agent that actually execute all the steps mentioned in a Job. When you create a Jenkins job, you have to assign an agent to it. Every agent has a label as a unique identifier.

When you trigger a Jenkins job from the master, the actual execution happens on the agent node that is configured in the job.

A single, monolithic Jenkins installation can work great for a small team with a relatively small number of projects. As your needs grow, however, it often becomes necessary to scale up. Jenkins provides a way to do this called “master to agent connection.” Instead of serving the Jenkins UI and running build jobs all on a single system, you can provide Jenkins with agents to handle the execution of jobs while the master serves the Jenkins UI and acts as a control node.

Pre-requisites

Let’s say we’re starting with a fresh Ubuntu 22.04 Linux installation. To get an agent working make sure you install Java ( same version as jenkins master server ) and Docker on it.

Note:- While creating an agent, be sure to separate rights, permissions, and ownership for jenkins users.

Step 1

Launch two instances, one agent and master server

These are the two servers, Master and Agent

Step 2

1. Install Java on Jenkins on Master and Agent

2. Install Jenkins on Master and Agent

3. Install Docker on Agent server

Step 3

Once, both servers are setup, we need to make sure the agent server can be connected from within Master server.

For this,

In the master instance, go to

cd .ssh/

Now type

ssh-keygen

Press enter key will be generated in id_rsa.pub

Now

cat id_rsa.pub

This will give us a public key of master

Copy the public key and go to agent server

Now, in agent server,

cd .ssh/

vim auth_keys

and paste the copied public key and save.

Now go back to agent server and type

ssh ubuntu@<agentserver-publicip>

You will directly connect to server

Step 4

Now lets create a agent on Jenkins GUI

Give node name.

Give name, desc, remote-root-dir(/home/ubuntu)

Give label as application to use in that server

Give usage details(as much as possible)

Give launch method ssh

in host give public ip of agent server

In credentials click add

In kind select ssh username with pvt key

In ID (dev-ssh-key)

Put description. Put username as ubuntu

Now in private key section, fetch id_rsa from jenkins master server and paste in private key

in known host verification, select non-verifying verification strategy.

Now save, open check and check, your agent is running

Step 5

Now create a Pipeline and run it on Node server.