The 12 Factor Methodology for Beginners

The 12 Factor methodology is a set of best practices for building scalable and maintainable web applications. It was created to make it easier to develop and deploy software in a consistent and efficient way. Imagine you're building a virtual pet store online, and we'll use a simple Python Flask application to explain each factor:

1. Codebase: Your pet store's code should be in a single codebase, tracked in a version control system (like Git). This way, everyone working on the project uses the same code.

2. Dependencies: Use a requirements.txt file to list all the Python packages your pet store needs to run. This ensures that everyone has the same dependencies installed.

3. Config: Store configuration in environment variables, like the database URL or secret keys. This makes it easy to change settings without altering code.

4. Backing Services: Treat services like databases or message queues as attached resources. For example, use environment variables to specify your database connection details.

5. Build, Release, Run: Separate the steps of building your code, releasing it, and running it. This ensures that you can deploy the same code consistently across different environments.

6. Processes: Run your pet store as a set of stateless processes. In our case, Flask will handle each HTTP request independently, without relying on server state.

7. Port Binding: Expose your pet store via a port (like 80 for HTTP). Flask typically runs on a port like 5000, and you can use a web server like Nginx to forward requests to it.

8. Concurrency: Scale your application horizontally by adding more instances. If you have lots of pet store visitors, run multiple copies of your Flask app to handle the load.

9. Disposability: Make your pet store easy to start and stop. If there's an issue, you can quickly replace or restart a part of your application.

10. Dev/Prod Parity: Keep development and production environments as similar as possible. This reduces bugs and surprises when you deploy.

11. Logs: Write logs to stdout (standard output) and let your hosting environment collect them. This makes it easy to monitor and troubleshoot.

12. Admin Processes: Run admin tasks as one-off processes. For example, you can create a script to update your pet store's product inventory.