CI/CD pipeline for Flask - Mini Project: Build & Apply

CI/CD Pipeline for Flask Application

📖 Scenario: You have created a simple Flask web application. Now, you want to automate testing and deployment using a CI/CD pipeline. This project will guide you through setting up the basic files and configuration to enable continuous integration and continuous deployment for your Flask app.

🎯 Goal: Build a basic CI/CD pipeline configuration for a Flask app that installs dependencies, runs tests, and deploys the app automatically.

📋 What You'll Learn

Create a simple Flask app file named app.py with a basic route.

Add a requirements file named requirements.txt listing Flask.

Create a GitHub Actions workflow file named ci-cd.yml to automate install, test, and deploy steps.

Print the deployment success message at the end.

💡 Why This Matters

🌍 Real World

Automating testing and deployment saves time and reduces errors when updating web applications.

💼 Career

CI/CD pipelines are essential skills for DevOps engineers and developers to deliver software reliably and quickly.

1

Create a simple Flask app

Create a file named app.py with a Flask app that has one route / returning the text "Hello, CI/CD!". Use the variable name app for the Flask instance.

Flask

# Your code here

Hint

Import Flask, create app = Flask(__name__), define a route / with a function returning the string.

2

Add requirements file

Create a file named requirements.txt containing the exact line Flask==2.3.2 to specify the Flask version dependency.

Flask

from flask import Flask
app = Flask(__name__)

@app.route('/')
def home():
    return "Hello, CI/CD!"

if __name__ == '__main__':
    app.run(debug=True)

# Create requirements.txt with Flask==2.3.2

Hint

Write Flask==2.3.2 exactly in requirements.txt to specify the Flask version.

3

Create GitHub Actions workflow

Create a file named .github/workflows/ci-cd.yml with a GitHub Actions workflow that triggers on push to main. The workflow should have a job named build that runs on ubuntu-latest. It should have steps to: checkout code, set up Python 3.12, install dependencies from requirements.txt, run tests by executing python -m unittest discover, and print Deployment successful! at the end.

Flask

from flask import Flask
app = Flask(__name__)

@app.route('/')
def home():
    return "Hello, CI/CD!"

if __name__ == '__main__':
    app.run(debug=True)

# Create .github/workflows/ci-cd.yml with the described workflow
# Your code here

Hint

Use GitHub Actions syntax to define a workflow triggered on push to main. Include steps for checkout, Python setup, install, test, and a final echo message.

4

Print deployment success message

Add a print statement in app.py after the Flask app runs to print "Deployment successful!" to the console.

Flask

from flask import Flask
app = Flask(__name__)

@app.route('/')
def home():
    return "Hello, CI/CD!"

if __name__ == '__main__':
    app.run(debug=True)

# Add print statement for deployment success below
# Your code here

Hint

Use print("Deployment successful!") after app.run() in app.py.

Practice

1. What is the main purpose of a CI/CD pipeline for a Flask application?

easy

A. To automate testing and deployment whenever code changes

B. To manually deploy code after testing

C. To write Flask application code faster

D. To create user interfaces automatically

Solution

1. Step 1: Understand CI/CD pipeline role

   A CI/CD pipeline automates the process of testing and deploying code changes to catch errors early and speed up delivery.

2. Step 2: Match purpose with options

   To automate testing and deployment whenever code changes correctly states automation of testing and deployment on code changes, which is the main goal of CI/CD.

3. Final Answer:

   To automate testing and deployment whenever code changes -> Option A

4. Quick Check:

   CI/CD automates testing and deployment = C [OK]

Hint: CI/CD means automatic test and deploy on code change [OK]

Common Mistakes:

• Thinking CI/CD writes code
• Confusing manual deployment with CI/CD
• Assuming CI/CD creates UI automatically

2. Which of the following is a correct minimal GitHub Actions workflow file name and location for a Flask CI/CD pipeline?

easy

A. .github/workflows/flask-ci.yml

B. github/actions/flask-ci.yaml

C. .github/actions/flask-ci.yml

D. workflows/.github/flask-ci.yml

Solution

1. Step 1: Identify GitHub Actions workflow file location

   GitHub Actions requires workflow files inside the repository at .github/workflows/ directory.

2. Step 2: Check file name and extension

   The file should have a .yml or .yaml extension. .github/workflows/flask-ci.yml uses correct directory and file name.

3. Final Answer:

   .github/workflows/flask-ci.yml -> Option A

4. Quick Check:

   Workflow files go in .github/workflows/ = D [OK]

Hint: GitHub Actions workflows live in .github/workflows/ [OK]

Common Mistakes:

• Placing workflow files outside .github/workflows/
• Using wrong file extensions
• Misnaming the directory

3. Given this GitHub Actions snippet for a Flask app:

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - name: Set up Python
        uses: actions/setup-python@v4
        with:
          python-version: '3.12'
      - name: Install dependencies
        run: pip install -r requirements.txt
      - name: Run tests
        run: pytest

What will happen when this workflow runs?

medium

A. It only installs dependencies without running tests

B. It checks out code, sets Python 3.12, installs dependencies, and runs tests

C. It runs tests without installing dependencies

D. It fails because Python version is missing

Solution

1. Step 1: Analyze each step in the workflow

   The workflow checks out the code, sets up Python 3.12, installs dependencies from requirements.txt, then runs pytest tests.

2. Step 2: Confirm all steps are present and correct

   All steps are correctly ordered and complete, so the workflow will perform all these actions successfully.

3. Final Answer:

   It checks out code, sets Python 3.12, installs dependencies, and runs tests -> Option B

4. Quick Check:

   Checkout + setup + install + test = B [OK]

Hint: Check steps order: checkout, setup, install, test [OK]

Common Mistakes:

• Assuming tests run without installing dependencies
• Thinking Python version is missing
• Ignoring the checkout step

4. You wrote this GitHub Actions step to install dependencies:

- name: Install dependencies
  run: pip install requirements.txt

Why does this step fail in your Flask CI/CD pipeline?

medium

A. Because pip install cannot run in GitHub Actions

B. Because requirements.txt file is missing

C. Because the command should be 'pip install -r requirements.txt'

D. Because Python version is not specified

Solution

1. Step 1: Identify the pip install syntax error

   The command 'pip install requirements.txt' tries to install a package named 'requirements.txt' instead of reading the file.

2. Step 2: Correct the command syntax

   The correct command to install from a requirements file is 'pip install -r requirements.txt'. This flag tells pip to read the file.

3. Final Answer:

   Because the command should be 'pip install -r requirements.txt' -> Option C

4. Quick Check:

   Use '-r' flag to install from file = A [OK]

Hint: Use 'pip install -r requirements.txt' to install dependencies [OK]

Common Mistakes:

• Omitting the '-r' flag
• Assuming pip install can't run in CI
• Blaming missing Python version

5. You want to deploy your Flask app automatically after tests pass using GitHub Actions. Which step should you add to your workflow to deploy to Heroku?

hard

A. Add a step that runs 'pip install flask-heroku'

B. Add a step that runs 'heroku login' interactively

C. Add a step that copies files to a local folder

D. Add a step using 'akhileshns/heroku-deploy@v3.12.12' action with Heroku API key and app name

Solution

1. Step 1: Understand automated deployment in GitHub Actions

   To deploy automatically, use a GitHub Action designed for Heroku deployment that accepts API keys and app name securely.

2. Step 2: Identify correct deployment action

   The 'akhileshns/heroku-deploy@v3.12.12' action is a popular choice for Heroku deployment in GitHub workflows.

3. Final Answer:

   Add a step using 'akhileshns/heroku-deploy@v3.12.12' action with Heroku API key and app name -> Option D

4. Quick Check:

   Use Heroku deploy action with API key = A [OK]

Hint: Use Heroku deploy GitHub Action with API key for auto deploy [OK]

Common Mistakes:

• Trying interactive login in CI
• Copying files locally instead of deploying
• Installing unrelated packages