The 12 Factor App is a methodology for building software-as-a-service apps that emphasizes portability, scalability, and maintainability. Developed by engineers at Heroku, the 12-factor methodology is intended to standardize and streamline app development and deployment. Below are the twelve factors in detail:

1. Codebase

• One codebase tracked in revision control, many deploys
• There should be a single codebase for a project, which is tracked in a version control system like Git. Multiple environments (e.g., production, staging, development) should be different deployments of the same codebase.

2. Dependencies

• Explicitly declare and isolate dependencies
• All dependencies should be declared explicitly in a dependency declaration file (e.g., requirements.txt for Python, package.json for Node.js). Use a dependency management tool to ensure these dependencies are isolated and versioned properly.

3. Config

• Store config in the environment
• Configuration that varies between deploys (such as credentials or resource handles) should be stored in the environment. This separates config from code, allowing for different configurations in different environments.

4. Backing Services

• Treat backing services as attached resources
• Backing services (e.g., databases, messaging systems, caches) should be treated as attached resources that can be attached and detached as needed, without making changes to the app's code.

5. Build, Release, Run

• Strictly separate build and run stages
• The build stage converts a code repo into an executable bundle (e.g., compiling code). The release stage takes the build and combines it with the current config to create a release. The run stage runs the app in the execution environment.

6. Processes

• Execute the app as one or more stateless processes
• The app should run as stateless processes, with any persistent data stored in a stateful backing service. This allows for easy scaling and resilience.

7. Port Binding

• Export services via port binding
• The app should be self-contained and make services available by listening on a port. This makes the app independent of the execution environment and easy to run.

8. Concurrency

• Scale out via the process model
• The app should be designed to scale out by running multiple instances of its processes. Use a process management tool to manage these processes effectively.

9. Disposability

• Maximize robustness with fast startup and graceful shutdown
• The app's processes should start up quickly and shut down gracefully. This improves resilience and allows for rapid deployment of changes.

10. Dev/Prod Parity

• Keep development, staging, and production as similar as possible
• Minimize the differences between development and production environments to catch issues early and ensure smoother deployments.

11. Logs

• Treat logs as event streams
• The app should not manage or write log files. Instead, it should treat logs as event streams that are sent to a centralized logging service for aggregation and analysis.

12. Admin Processes

• Run admin/management tasks as one-off processes
• Administrative or management tasks (e.g., database migrations) should be run as one-off processes in the same environment as the app, using the same codebase and config.

Adhering to these principles helps developers create applications that are more scalable, maintainable, and portable across different environments, ensuring a smoother development and deployment process.