The twelve factors

Overview

In the modern era, software is commonly delivered as a service: called web apps, or software-as-a-service. The twelve-factor app is a methodology for building software-as-a-service apps that:

• Use declarative formats for setup automation, to minimize time and cost for new developers joining the project;
• Have a clean contract with the underlying operating system, offering maximum portability between execution environments;
• Are suitable for deployment on modern cloud platforms, obviating the need for servers and systems administration;
• Minimize divergence between development and production, enabling continuous deployment for maximum agility;
• And can scale up without significant changes to tooling, architecture, or development practices.

The twelve-factor methodology can be applied to apps written in any programming language, and which use any combination of backing services (database, queue, memory cache, etc).

The Twelve Factors

Codebase

One codebase tracked in revision control, many deploys

Dependencies

Explicitly declare and isolate dependencies

Config

Store config in the environment

Backing services

Treat backing services as attached resources

Build, release, run

Strictly separate build and run stages

Processes

Execute the app as one or more stateless processes

Port binding

Export services via port binding

Concurrency

Scale out via the process model

Disposability

Maximize robustness with fast startup and graceful shutdown

Dev/prod parity

Keep development, staging, and production as similar as possible

Logs

Treat logs as event streams

Admin processes

Run admin/management tasks as one-off processes