The Twelve-Factor App: A Guideline for Building Modern Web Applications

The Twelve-Factor App: A Guideline for Building Modern Web Applications
Photo by Michael Skok / Unsplash


In the realm of software development, the Twelve-Factor App methodology onced garnered significant attention as a guide for building scalable, maintainable, and portable software-as-a-service applications.

I guess.

To be honest, I hadn't really thought about it specifically in some years until a recent job posting mentioned it alongside the SOLID & ACID principles (etc.).

The methodology was crafted by engineers at Heroku with experience in meeting the intricate challenges that come with SaaS development. It outlines twelve principles or "factors" designed to be a blueprint for modern web architectures.

I thought, given my lack of recollection, that writing an overview of these factors, explaining their significance and how they can be applied might be helpful for me.

Perhaps it will be helpful for you as well.

The Twelve Factors

1. Codebase

Principle: One codebase tracked in version control, multiple deploys

Significance: Having a single codebase ensures uniformity and ease of collaboration. Version control systems like Git enable tracking changes and coordinating work among multiple developers.

2. Dependencies

Principle: Explicitly declare and isolate dependencies

Significance: Dependencies should be explicitly declared to prevent any surprises during deployment or maintenance. This isolation simplifies troubleshooting and enhances portability.

3. Config

Principle: Store configuration in the environment

Significance: Configuration settings should be externalized from the codebase and read from the environment. This enables easy modification without code changes, providing flexibility in deployment.

4. Backing Services

Principle: Treat backing services as attached resources

Significance: Whether it's a database, a messaging queue, or a caching layer, backing services should be loosely coupled to the codebase. This allows for easy replacement and upgrades without affecting the application.

5. Build, Release, Run

Principle: Strictly separate build and run stages

Significance: The build, release, and run stages should be distinct to minimize errors and maximize deployability. This ensures that any change goes through a well-defined pipeline before it impacts users.

6. Processes

Principle: Execute the app as one or more stateless processes

Significance: Applications should be stateless to enable effortless scaling. State should be externalized to backing services like databases to maintain this statelessness.

7. Port Binding

Principle: Export services via port binding

Significance: Applications should be self-reliant, exposing services through binding to ports. This makes them easy to containerize and deploy using modern orchestration tools.

8. Concurrency

Principle: Scale out via the process model

Significance: Applications should be built to scale horizontally, meaning they can handle more traffic by adding more instances rather than upgrading a single instance's resources.

9. Disposability

Principle: Maximize robustness with fast startup and graceful shutdown

Significance: Applications should be designed to start quickly and shut down gracefully. This resilience enables seamless deployments and scaling operations.

10. Dev/Prod Parity

Principle: Keep development, staging, and production as similar as possible

Significance: A consistent environment across development, staging, and production minimizes surprises during deployment, making life easier for both developers and operations teams.

11. Logs

Principle: Treat logs as event streams

Significance: Logs should be viewed as a continuous stream of events rather than static files. This enables real-time monitoring and analysis.

12. Admin Processes

Principle: Run admin/management tasks as one-off processes

Significance: Administrative tasks, like database migrations, should be performed as one-off processes to ensure they are repeatable, auditable, and isolated from the application.


The Twelve-Factor App methodology offers a set of best practices that aim to optimize various aspects of a web application, from codebase management to how configuration and logging are handled. Adopting these principles can dramatically improve the maintainability, scalability, and portability of your applications.

I realized, while reacquainting myself with this list, that these are indeed best practices for web applications. While these are rather tailored specifically to a host like Heroku, they're still a good set of guidelines regardless of your cloud provider (for example, the job listing that triggered this post wanted familiarity with GCP and/or AWS).