Jenkins Installation Steps with WAR file in Linux

Version — 2.289.2 LTS Installation Type — Deployment of WAR File Mounting of /opt partition

We will be creating a new Volume group from the newly attached 500 Gb disk and then Create a new Logical Volume out of it

sudo vgcreate vg01 /dev/xvdb

sudo lvcreate -l 100%FREE — name lvol01 vg01

Once Logical Volume is created, we assign File System type to it which is ext4 in our case

sudo mkfs -t ext4 /dev/vg01/lvol01

After that, we create a directory /opt and assign our 500Gb Volume to the /opt folder

sudo mkdir -p /opt

sudo echo ‘/dev/vg01/lvol01 /opt ext4 defaults 1 2’ >> /etc/fstab

Then we run the mount command which will now mount the /opt as a new partition

sudo mount -a

You can verify by running the df -h command

cd /opt/

Next, we will be installing Jenkins and other requirements in /opt partition

Summary

· Install Java Version 8 — Jenkins is a Java-based application, hence Java is a must.

· Install Apache Tomcat Version 9 — Tomcat is required to deploy Jenkins war file.

· Download Jenkins war File — This war is required to install Jenkins.

· Deploy Jenkins war File — Jenkins war file needs to be deployed using Tomcat to run Jenkins.

· Install Suggested Plugins — Install a list of plugins suggested by Jenkins.

Installing prerequisites

Run the below commands as the root user,

yum install java-1.8.0-openjdk git

yum install wget

cd /opt/

wget https://archive.apache.org/dist/tomcat/tomcat-9/v9.0.50/bin/apache-tomcat-9.0.50.tar.gz

tar –xvzf apache-tomcat-9.0.50.tar.gz

Configuring Tomcat server

We have to create an Admin user and assign roles to him to proceed

vi /opt/apache-tomcat-9.0.50/conf/tomcat-users.xml

Add the below line into that file

<user username=”<some-tomacat-user>” password=”<some-tomacat-pwd>” roles=”manager-gui,admin-gui,manager-script,standard”/>

We can try running the Tomcat Apache server without any application by

cd /opt/apache-tomcat-9.0.50/bin

./ catalina.sh start

You can get the hostname of the Server using ifconfig command and try accessing the below URL

http://< your hostname>:8080

You will be redirected to the Tomcat Apache Manager page

Here try selecting the Manager Tool button

You will face an error like access denied, this is because by default Tomcat will allow the only browser from the machine which hosts the Apache Server

So we need to make a change in context.xml

cd /opt/apache-tomcat-9.0.50/webapps/manager/META-INF

Open the file context.xml and comment on the Valve configuration line alone, check below

<! — <Valve className=”org.apache.catalina.valves.RemoteAddrValve”

allow=”127\.\d+\.\d+\.\d+|::1|0:0:0:0:0:0:0:1" /> →

Restart Tomcat server by going to bin path again,

./ catalina.sh stop

./ catalina.sh start

Deploying the Jenkins WAR file into Tomcat Server

You can find the Latest Jenkins LTS version in this page — https://www.jenkins.io/download/

Download the Generic Java package and move it to server using WinSCP (or)

Use this command to download it directly to the server

wget https://get.jenkins.io/war-stable/2.289.2/jenkins.war

Once downloaded move the WAR file to the path — /opt/apache-tomcat-9.0.50/webapps/

Moving to this path will directly deploy the Application into Tomcat

We have to perform a restart to load the Application in Tomcat

But very important before, restarting you have to mention the JENKINS_HOME variable otherwise it will automatically set to the user home directory (i.e root in our case)

Open .bash_profile file of Root user and Jenkins home variable

vi ~/.bash_profile

Add this line inside the file — export JENKINS_HOME=/opt/JenkinsHome

Perform restart again

Now if you open the Manage Tool page of Tomcat Apache, You could see the Jenkins under the Application Table

Now Try accessing this — http://< your hostname>:8080/Jenkins

You will land on Unlock Jenkins Page, this means that our Jenkins is up and running.

Configuring in Jenkins UI

Once you hit the URL, you will be prompted to unlock Jenkins using the Initial Admin password placed at this path

{ JENKINS_HOME_PATH}secrets/initialAdminPassword

Enter the Password

Install the Suggested Plugins

Create your First Admin User

Then there you Jenkins is ready

Validate the Jenkins home path once by checking under

Manage Jenkins à Configure System

Adding Agent/Slave Nodes to Jenkins

We need Java and GIT installed in Agent Nodes to perform Jenkins Operations

yum –y install java-1.8.0-openjdk git

It is advisable to use the same user across all the Jenkins Master and Agent nodes

In our case since we ran Tomcat and deployed Jenkins WAR files as the root users, we are going to use root everywhere

We need to connect Master to Agent nodes to Integrate them

Go into the Master server and run the ssh-keygen command as the root user

Command — ssh-keygen

Example screenshot

It will ask you for the location to store the id_rsa (Private key) and id_rsa.pub (Public key) by default it is the home directory so proceed by giving enter

It is better to provide a passphrase, so note it down somewhere safe

Once done, you can find the files under the folder .ssh in the Root home directory

Creating Passwordless SSH between Master and Agent Node

We need to copy the id_rsa.pub key and paste it in the authorized_keys file of the Agent nodes which Master Jenkins will be accessing

Authorized_keys file will be present inside user home directory (In our case it is root) under .ssh folder

If not present create a file and paste the public key in it

cd ~/.ssh

vi authorized_keys

Once this is done, try to ssh from Master Server to the Slave Node (Both users are root)

ssh root@<your agent node host>

It will prompt you to confirm that this is a Verified Host, proceed by giving yes

This will add it in the known_host file, which will be useful for selecting strategy as Known Host Verification in Jenkins UI while adding the Agent Node

Adding the Agent Node from Jenkins UI

Once done go to Jenkins UI and under

Manage Jenkins à Mange Nodes and Clouds

Select New Node, Enter the Node name and select the Radio button Permanent Agent and give next

Proceed by entering the Name, Description. No. of executors you require and Remote Directory

It is advisable to use the same Home directory structure in the Master in Agent node as well, so create the Remote directory (Eg /opt/JenkinsHome) in the Agent server first and then enter the same path in the Remote Directory section

Select the Usage as Use the Node as much as possible

And Launch Method as Launch Agent via SSH

Enter the Hostname details

Under Credentials, Select Add and choose Jenkins

Select the Kind as SSH username with Private key and Scope as Jenkins

Enter the ID (Eg Master-To-Node-Key), Username and select the checkbox Treat Username as Secret

Choose Enter Directly and Enter the id_rsa (Private key) content of the Master Jenkins server in that section

(Those who have the Private key can access any machine which contains respective public key in their authorized_keys file)

Finish by giving Add

Now Select the Credentials which you just now created

Select the Host Key Verification Strategy as Know Host file Verification Strategy which we previously discussed

Leave others to default and Finish by giving Save.

Master Jenkins will now try to launch the Agent node, which will come online in few minutes.

You can confirm the node is up by checking under the build Executor Tab on the Jenkins Home page, you can see the Node name with the number of Executors which you entered while creating the Node.

So we have brought up the Jenkins and have Integrated the Node Agents as well, follow the same steps if you want another Node to be added.

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