Reference of the twelve- factor app book (http://12factor.net/).

twelve-factor-app.markdown

The twelve-factor app

I. Codebase

One codebase tracked in revision control, many deploys

II. Dependencies

Explicitly declare and isolate dependencies

III. Config

Store config in the environment

The app stores config in environment variables that are easy to change between deploys without changing any code. They are never grouped together as "environments" (does not scale), but instead are independently managed for each deploy.

IV. Backing Services

Treat backing services as attached resources

The code for an app makes no distinction between local and third party services.

V. Build, release, run

Strictly separate build and run stages

VI. Processes

Execute the app as one or more stateless processes

Processes are stateless and share-nothing. Any data that needs to persist must be stored in a stateful backing service, typically a database. Sticky sessions are a violation and should never be used or relied upon.

VII. Port binding

Export services via port binding

VIII. Concurrency

Scale out via the process model

IX. Disposability

Maximize robustness with fast startup and graceful shutdown

X. Dev/prod parity

Keep development, staging, and production as similar as possible

Make the following gap as small as possible:

• The time gap: Time between writing code and deploy of it.
• The personell gap: Developers write code, ops deploy it.
• The tools gap: Development and production tools.

XI. Logs

Treat logs as events streams

The app never concerns itself with routing or storage of its output.

XII. Admin processes

Run admin/management tasks as one-off processes