exercise2

Python Application with Podman

Table of Contents

• Introduction
• What is Docker?
• What is Podman?
• Project Structure
• Dockerfile Explanation
• Prerequisites
• Building the Container Image
• Running the Container
• Conclusion
• Final Objective

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Introduction

This exercise focuses on containerizing a Python application and running it using Podman, a modern container management tool. You will learn how to build a container image and run it locally, enabling you to work with containerized environments in a secure and rootless manner.

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What is Docker?

Docker is a popular platform used for developing, shipping, and running applications inside containers. Containers allow developers to package an application with all its dependencies and run it in a consistent environment across different systems. Docker provides:

• Simplified container management.
• Compatibility across multiple platforms.
• A daemon-based approach to container orchestration.

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What is Podman?

Podman is an open-source container engine similar to Docker but without requiring a background daemon. Key features include:

• Daemonless and rootless operation for enhanced security.
• Full compatibility with Dockerfiles.
• Support for running containers in environments where Docker is not available or needed.

Unlike Docker, Podman does not require root access and provides improved security for managing containers.

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Project Structure

Here is the project structure for this exercise:

exercises/exercise2/
├── Dockerfile
├── Infra.png
├── README.md
├── app.png
└── app.py

• Dockerfile: Contains the instructions for building the container image.
• Infra.png: Diagram or visualization of the application's infrastructure.
• README.md: This file contains instructions for the exercise.
• app.png: Screenshot of the application running.
• app.py: Python script for the application.

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Dockerfile Explanation

The Dockerfile is a script that contains a series of instructions to automate the creation of a container image. Here is what each instruction in the provided Dockerfile does:

# Use the official Python image from Docker Hub
FROM python:3.9-slim

# Set the working directory inside the container
WORKDIR /app

# Copy the application code into the container
COPY app.py .

# Install the Python dependencies (if any)
RUN pip install flask

# Specify the command to run the application
CMD ["python", "app.py"]

Explanation:

1. FROM: Specifies the base image (Python 3.9 slim version) for the container.
2. WORKDIR: Sets the working directory inside the container to /app.
3. COPY: Copies the app.py file from the host to the container's working directory.
4. RUN: Installs the flask package inside the container.
5. CMD: Defines the command to run the Python application when the container starts.

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Prerequisites

Before you start, ensure the following:

• Podman installed on macOS. Follow the Podman installation guide or use:

  brew install podman

• Basic understanding of Python and containerization concepts.
• Completion of Exercise #1.

For macOS users new to Podman, initialize and start the Podman machine:

podman machine init
podman machine start

Verify that Podman is working with:

podman info

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Building the Container Image

1. Navigate to the exercise2 directory:

   cd sre-abc-training/exercises/exercise2

2. Build the container image:

   podman build -t my-python-app .

   • -t my-python-app: Assigns the tag my-python-app to the image.
   • .: Specifies the current directory containing the Dockerfile.

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Running the Container

Run the container using Podman:

podman run --rm -it -p 5000:5000 my-python-app

Explanation of flags:

• --rm: Removes the container after it stops.
• -it: Runs the container interactively.
• -p 5000:5000: Maps port 5000 on the container to port 5000 on the host.

Access the application by visiting:

http://127.0.0.1:5000/

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Conclusion

You have now successfully containerized and run a Python application using Podman. This exercise demonstrates the basics of containerization and prepares you for more advanced deployment scenarios.

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Final Objective

At the end of this exercise, you should accomplish the following:

[!IMPORTANT] Once the container is running, open your web browser and go to http://127.0.0.1:5000/. You should see the text "Hello, World!" displayed.

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