dev-ops-challenges

Set Up Jenkins Server

Technical Overview

Deploying a continuous integration and continuous deployment (CI/CD) server like Jenkins requires setting up a Java runtime environment (JRE) and configuring official package repositories to ensure clean lifecycle management.

Jenkins operates as a standalone Java application hosting its own embedded servlet container (Jetty). In a standard Linux infrastructure, installing Jenkins involves:

Java Environment Provisioning: Installing a supported Java Runtime Environment (JRE).
Package Repository Configuration: Adding the official Jenkins Debian repository and registering its GPG key to verify package signatures.
Daemon Integration: Managing Jenkins as a background service via system init scripts (service or systemctl).
Initial Setup Wizard: Unlocking the application using a generated file-based secret, installing baseline plugins, and creating the master admin user account.

graph TD
    subgraph ClientSystem ["Client System"]
        User["CI/CD Administrator"]
    end

    subgraph TargetServer ["Jenkins Target Server"]
        APT["APT Package Manager"]
        Java["OpenJDK 21 JRE"]
        JenkinsService["Jenkins Daemon on Port 8080"]
        JenkinsKeyring["GPG Keyring File"]
        JenkinsSource["Jenkins Source File"]
        SecretPath["Unlock Keyfile Secret"]
        SetupWizard["Web Setup Wizard"]
    end

    APT -->|Installs| Java
    APT -->|Installs| JenkinsService
    JenkinsKeyring -.->|Verifies Signatures| APT
    JenkinsSource -.->|Configures Repo| APT
    SecretPath -->|Unlock Code| SetupWizard

    User -->|SSH as root| APT
    User -->|HTTP Access| SetupWizard

Debian Repositories & Java Service Architecture Deep Dive

1. Secure Package Management with APT GPG Keys

Debian-based distributions use GPG (GNU Privacy Guard) keys to sign package metadata. This guarantees that packages installed using apt have not been tampered with.

Keyring Registry: GPG keys are downloaded and saved into a secure keyring directory (such as /etc/apt/keyrings/).
Sources List Configuration: The repository definition /etc/apt/sources.list.d/jenkins.list is configured with a signed-by option pointing directly to this keyring. When apt update runs, the package manager checks the downloaded package metadata against this local key.

2. Servlet Containers & JRE Prerequisites

Jenkins is written in Java and runs inside a servlet container.

Version Compatibility: Modern versions of Jenkins require Java 17 or Java 21. Running Jenkins on unsupported versions of Java will cause compilation errors or application failure upon startup.
Dependency Management: The openjdk-21-jre package installs the core Java Virtual Machine (JVM). Additionally, graphic libraries (e.g., fontconfig) are installed to support PDF rendering, graph generation, and user interface elements.

Infrastructure & Configuration Requirements

Target Server Hostname: jenkins
User Credentials: root (Password: S3curePass)
Installation Utility: apt (Debian-based package manager)
Service Manager: service CLI utility

Jenkins Admin User Specification

Username: theadmin
Password: Adm!n321
Full Name: Rose
E-mail Address: rose@jenkins.stratos.xfusioncorp.com

Step-by-Step Installation

Step 1: Connect to the Jenkins Server

Establish an SSH connection to the destination server using the target host and credentials:

ssh root@jenkins
# Enter password: S3curePass

Step 2: Install Java Runtime Environment (JRE)

Update the package registry index and install the OpenJDK runtime dependency along with system font helpers:

sudo apt update
sudo apt install -y fontconfig openjdk-21-jre

Verify that the JVM has been successfully added to the executable search path:

java -version

Expected Output:

openjdk version "21.0.x" ...
OpenJDK Runtime Environment ...
OpenJDK 64-Bit Server VM ...

Step 3: Add the Official Jenkins Repository

Download and save the Jenkins repository GPG key into the system keyrings directory:

sudo wget -O /etc/apt/keyrings/jenkins-keyring.asc https://pkg.jenkins.io/debian-stable/jenkins.io-2026.key

Add the Jenkins package repository source file pointing to the keyring:

echo "deb [signed-by=/etc/apt/keyrings/jenkins-keyring.asc] https://pkg.jenkins.io/debian-stable binary/" | sudo tee /etc/apt/sources.list.d/jenkins.list > /dev/null

Step 4: Install Jenkins Package

Update the package source cache to discover the new Jenkins repository index, then install the package:

sudo apt update
sudo apt install -y jenkins

Step 5: Start the Jenkins Daemon Service

Start the Jenkins background service using the system init CLI utility:

# Check initial status
service jenkins status

# Start the background daemon
service jenkins start

Confirm that the service is running and listening on default port 8080:

service jenkins status

Expected Output:

● jenkins.service - LSB: Start Jenkins at boot time
     Loaded: loaded (/etc/init.d/jenkins; generated)
     Active: active (running) since Wed 2026-07-22 20:25:00 UTC; 10s ago
     ...

Initial Setup Wizard Walkthrough

Step 1: Retrieve the Initial Admin Password

To unlock the Jenkins administrative interface, read the generated unique password hash from the local filesystem:

cat /var/lib/jenkins/secrets/initialAdminPassword

Expected Output:

a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6

Copy the output hash, paste it into the Administrator password field on the Jenkins landing page (http://<server-ip>:8080), and click Continue.

Unlock Jenkins

Step 2: Install Suggested Plugins

On the customize page, click the Install suggested plugins option. This installs basic plugins for source control (Git), pipelines, credentials management, and node configurations.

Customize Jenkins