What is the Twelve-Factor App

The Twelve-Factor App is a methodology for building modern applications, particularly web-based and Software as a Service (SaaS) applications. It outlines a set of twelve best practices aimed at improving scalability, maintainability, and portability. These principles facilitate the development of applications that can effortlessly transition between different stages, from development to deployment, and operate efficiently in cloud environments.

Twelve Factors

I will dissect each of the twelve factors and explore their significance, applications, and best practices.

Factor 1: Codebase

One Codebase, Multiple Deployments

The first factor dictates that an application should have a single codebase that is tracked in a version control system. Multiple deployments can be made from this codebase. This principle encourages maintainability and consistency across different stages of the application's lifecycle.

Using version control systems like Git, Mercurial, or SVN, developers can efficiently manage the codebase, keep track of changes, collaborate, and avoid conflicting versions of code.

Version Control

Version control is an essential aspect of modern software development. It not only provides a historical record of code changes but also enables multiple contributors to work simultaneously without overwriting each other's work. It is imperative to use version control for the codebase and make it the source of truth for your application.

Factor 2: Dependencies

Managing Dependencies

Dependencies are external libraries and tools that your application relies on. The second factor suggests explicitly declaring and isolating dependencies, rather than assuming that they exist in the environment. By doing so, you can ensure that your application runs consistently across various environments.

Dependency Isolation

Tools like virtual environments in Python, npm in Node.js, and Bundler in Ruby, allow you to isolate your application’s dependencies. This isolation ensures that your application does not implicitly rely on system-wide packages, which can lead to version conflicts and inconsistencies between environments.

Factor 3: Config

Configuration and Code Separation

The third factor emphasizes the importance of separating configuration from code. Configuration includes everything likely to vary between deployments, such as database credentials, API keys, and environment-specific settings. Storing these settings in the codebase can lead to security vulnerabilities and reduced portability.

Environmental Variables

Environment variables are a common method for managing configuration. They allow you to keep configuration separate from the codebase and can easily be modified without altering the code.

Factor 4: Backing Services

Treating Backing Services as Attached Resources

Backing services, such as databases, messaging systems, or caching, should be treated as attached resources. This means the application should not distinguish between local and third-party services.

Loose Coupling

This abstraction promotes loose coupling and portability, as the application can easily switch between different service providers without code changes. Configuration details such as service endpoints and credentials should be stored in environment variables.

Factor 5: Build, Release, Run

The Deployment Process

The fifth factor separates the deployment process into three stages: build, release, and run. The build stage involves compiling code and resolving dependencies. The release stage combines the build with the configuration. The run stage executes the application in the execution environment.

Immutable Releases

Once a release is created, it should be immutable, meaning no changes can be made to it. If changes are needed, a new release should be created from the build stage.

Factor 6: Processes

Stateless Processes

The sixth factor advises that applications should be executed as one or more stateless processes. This means that they should not rely on the local storage for persistence, as it is usually ephemeral in cloud environments.

Process Scaling

Statelessness enables the application to scale horizontally by adding more processes. Each process should be independent and share nothing with other running processes.

Factor 7: Port Binding

Self-Containing Services

Applications should be self-contained and not rely on a runtime injection of a webserver into the execution environment. They should be capable of binding themselves to a port to serve requests.

Exporting Services via Port Binding

This factor emphasizes that the web app should be able to bind to a port and listen for incoming requests without relying on an external web server. This makes scaling, deploying, and managing the application easier and more flexible.

Factor 8: Concurrency

Process Model

Concurrency in the context of the Twelve-Factor App refers to the ability of the application to scale horizontally, i.e., by adding more running instances rather than scaling vertically by adding more power to an existing instance. The application should be architected as a collection of small processes that communicate over a backplane.

Scaling Out via the Process Model

This allows for the application to be scaled out easily by simply adding more processes. Different types of work can be assigned to different types of processes, and you can scale them independently based on workload requirements.

Factor 9: Disposability

Fast Startup and Graceful Shutdown

Applications should be able to start quickly and should also be able to shut down gracefully when they receive a signal to do so. This ensures that they can be rapidly and reliably scaled, deployed, and released.

Robustness with Disposable Components

Making components disposable ensures that the system can recover from failures and changes automatically, enhancing its robustness and resilience.

Factor 10: Dev/Prod Parity

Continuous Deployment

This factor emphasizes the importance of keeping development, staging, and production environments as similar as possible. This helps in identifying and addressing issues early in the development cycle and facilitates continuous deployment.

Keeping Development, Staging, and Production as Similar as Possible

By ensuring that the gap between development and production is small, teams can understand and address production issues more efficiently and reliably. This involves using similar backing services, databases, and environmental configurations.

Factor 11: Logs

Log Streams

Applications should not be concerned with managing log files. Instead, they should write logs to the standard output, allowing the execution environment to capture the logs.

Log Management and Monitoring

In production, it is important to have a log management system that aggregates log streams, monitors, and alerts based on them. This helps in debugging, monitoring performance, and understanding user behavior.

Factor 12: Admin Processes

Running Administrative Tasks

One-off administrative tasks, such as database migrations, should be run in an environment identical to the application’s regular long-running processes.

One-off Processes

This ensures that all administrative tasks are performed under the same circumstances as the application, reducing discrepancies and unexpected behavior. One-off processes should be automated and managed through code in the version control system.

References

https://12factor.net