Lab 21: Jenkins Pipeline for Local CI¶

Objective

By the end of this lab, you will be able to: - Create a Jenkins Pipeline for building, testing, and deploying a Dockerized app - Deploy the app locally using Docker via Jenkins

Prerequisites

Jenkins is up and running (from Lab 18)
Flask app is built (Lab 19)
Docker installed on the host machine (Lab 17)

Step 1: Prepare GitHub Repository¶

1.1 Fork or clone the Flask app repository¶

git clone https://github.com/Sid-Trainings/flask-sample-webapp.git
cd flask-sample-webapp

1.2a Push it to your own GitHub repo¶

Using SSHUsing HTTP(S)

git remote rename origin upstream
git remote add origin git@github.com:<your_username>/flask-sample-webapp.git
git add .
git commit -m "added Dockerfile"
git push -u origin main

git remote rename origin upstream
git remote add origin https://github.com/skarkhanis95/flask-sample-webapp.git
git add .
git commit -m "added Dockerfile"
git push -u origin main

Step 2: Configure GitHub Credentials in Jenkins¶

Go to Manage Jenkins > Credentials
Under (global), click Add Credentials
Choose Username and Password
Add your GitHub username and Personal Access Token (PAT)
Save it with an ID like github-creds

Step 3: Recreate Jenkins Container with Docker Access¶

If Jenkins is running inside Docker, stop and recreate the container with required permissions:

3.1 Stop and remove Jenkins¶

docker stop jenkins
docker rm jenkins

3.2 Run Jenkins as root and mount Docker socket¶

docker run -d \
  --name jenkins \
  -u root \
  -p 8080:8080 -p 50000:50000 \
  -v jenkins_home:/var/jenkins_home \
  -v /var/run/docker.sock:/var/run/docker.sock \
  jenkins/jenkins:lts

3.3 Remove your local python app from Docker socket¶

docker ps

Note the Container ID or Container Name of your local python app. At this point you should have 2, one for Jenkins and one for your local Python Flask App

docker stop <your_flask_app_container_id_or_name>
docker rm <your_flask_app_container_id_or_name>

Step 4: Install Docker CLI Inside Jenkins Container¶

4.1 Enter the container as root¶

docker exec -u 0 -it jenkins bash

4.2 Install Docker¶

apt update
apt install -y docker.io

4.3 Verify Docker is working¶

docker version

This should show both Docker client and server info (the server comes from host)

Type exit to leave the container.

Step 5: Create Jenkins Pipeline Job¶

Go to Jenkins Dashboard > New Item
Enter job name, select Pipeline, click OK
Scroll to Pipeline section
Choose Pipeline script from SCM
Select Git, and enter your GitHub repo URL
Use github-creds if prompted for credentials
Set the branch to main
Save the job

Step 6: Add Jenkinsfile to GitHub Repo¶

In the root of your Flask repo, create a file named Jenkinsfile:

nano Jenkinsfile
Copy the below code and paste into Nano editor

Modify the file below to replace with your actual GitHub username

pipeline {
  agent any

  stages {
    stage('Clone Repository') {
      steps {
        git url: 'https://github.com/<your-github-username>/flask-sample-webapp.git', branch: 'main'
      }
    }

    stage('Build Docker Image') {
      steps {
        sh 'docker build -t flask-demo-app .'
      }
    }

    stage('Run Container') {
      steps {
        sh 'docker stop flask-container || true'
        sh 'docker rm flask-container || true'
        sh 'docker run -d --name flask-container -p 5000:5000 flask-demo-app'
      }
    }
  }
}

Replace your username

Replace <your-github-username> with your actual GitHub username.

Save and Exit the nano editor using Ctrl+O --> press Enter --> Crtl+X

6.1 Push Jenkinsfile to GitHub¶

git add Jenkinsfile
git commit -m "Add Jenkins pipeline"
git push origin main

Step 7: Run Your Pipeline¶

Open Jenkins
Go to your pipeline job
Click Build Now
Monitor output in the Console Output tab

Verification¶

In your host browser, visit:
```
http://<VM-IP>:5000
```
You should see your Flask web app running via a container created by Jenkins

💡 Make sure your Flask app uses app.run(host='0.0.0.0', port=5000) to allow external access