🚀 Day 8/30 — Jenkins Setup & Freestyle Project | DevOps Interview Preparation

Welcome to Day 8 of the 30 Days of DevOps Interview Preparation Challenge!
Today, we’ll cover Jenkins, one of the most widely used CI/CD automation tools, and learn how to set it up along with our first Freestyle Project.

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📖 1. Understanding Jenkins

Jenkins is an open-source automation server written in Java. It helps automate:

• Building code

• Running tests

• Deploying applications
  … all in a continuous integration and continuous delivery (CI/CD) pipeline.

Key Features:

• Plugin Ecosystem: 1,800+ plugins to integrate with SCMs, build tools, cloud platforms.

• Cross-Platform: Runs on Windows, macOS, Linux.

• Extensible: Supports both Freestyle jobs and scripted pipelines.

• Integration: Works with GitHub, Bitbucket, GitLab, AWS, Docker, Kubernetes, etc.

Why Jenkins is Popular in DevOps:

• Free & Open Source

• Huge community support

• Flexible for small teams & enterprises

• Easy to install and configure

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🏗 2. Setting up Jenkins on AWS EC2

We’ll use Ubuntu 22.04 EC2 Instance for this setup.

Step 1 — Launch an EC2 Instance

1. Go to AWS Console → EC2 → Launch Instance.

2. Select Ubuntu 22.04 LTS.

3. Instance type: t2.small or higher.

4. Configure security group:

   • Allow SSH (22) from your IP.

   • Allow HTTP (80) from Anywhere.

   • Allow Custom TCP 8080 from Anywhere.

5. Launch the instance.

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Step 2 — Install Java

sudo apt update
sudo apt install -y openjdk-17-jdk
java -version

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Step 3 — Install Jenkins

curl -fsSL https://pkg.jenkins.io/debian/jenkins.io.key | sudo tee \
  /usr/share/keyrings/jenkins-keyring.asc > /dev/null

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

sudo apt update
sudo apt install -y jenkins

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Step 4 — Start & Enable Jenkins

sudo systemctl start jenkins
sudo systemctl enable jenkins

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Step 5 — Access Jenkins UI

1. Open browser:
   http://<EC2-Public-IP>:8080

2. Get admin password:

sudo cat /var/lib/jenkins/secrets/initialAdminPassword

3. Paste it in the UI → Install Suggested Plugins.

4. Create Admin User → Save.

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🛠 3. Creating Your First Freestyle Project

A Freestyle Project in Jenkins is a flexible, simple job configuration for building and deploying projects.

Steps:

1. On Jenkins Dashboard → Click New Item.

2. Enter a name → Select Freestyle project → OK.

3. Source Code Management:

   • Select Git

   • Enter GitHub repo URL

   • Add credentials if private.

4. Build Triggers:

   • Optionally enable Poll SCM or Build periodically.

5. Build Steps:

   • Click Add build step → Select Execute shell.

   • Example:

       echo "Building project..."
       mvn package
     

6. Save → Click Build Now.

7. Check Console Output to see logs.

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🎯 4. Interview Preparation Guide

Common Jenkins Interview Questions:

Q1: What is Jenkins and why do we use it?
A: Jenkins is an open-source automation server that helps implement CI/CD by automating the build, test, and deployment processes. It increases software delivery speed, ensures consistency, and reduces human errors.

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Q2: What is the difference between Freestyle and Pipeline jobs?
A:

• Freestyle: GUI-based configuration, simpler, less scalable for complex workflows.

• Pipeline: Code-as-configuration (Jenkinsfile), better for complex, multi-step, version-controlled pipelines.

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Q3: How can you secure Jenkins?
A:

• Enable authentication & authorization.

• Use Role-Based Access Control (RBAC) plugins.

• Secure Jenkins with HTTPS.

• Restrict script execution.

• Keep Jenkins and plugins updated.

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Q4: How do you integrate GitHub with Jenkins?
A:

• Install Git plugin.

• Configure GitHub webhook to http://<jenkins-url>/github-webhook/.

• Add repo URL in job SCM settings.

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Q5: What are some useful plugins for Jenkins?
A:

• Git plugin

• Pipeline plugin

• Email Extension

• Blue Ocean UI

• Docker plugin

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💡 Pro Tips for Real Projects

• Use Pipeline jobs for scalability, Freestyle for quick tasks.

• Keep Jenkins jobs & configs in source control.

• Set up build notifications (Slack, Email).

• Use agents for isolated builds to avoid conflicts.

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📌 Conclusion:
Today, we learned how to set up Jenkins on AWS EC2, create our first Freestyle Project, and prepare for Jenkins-related interview questions. Tomorrow, we’ll go deeper into Jenkins Pipeline Projects.

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