As of writing this book, 12-factor applications has emerged as a way of developing Software as a Service (SaaS) applications. The 12-factor application approach define 12 software development principles. The motivations behind these principles aim to minimize time and effort, avoid software erosion, and embrace Continuous Delivery and cloud platforms.

In other words the 12-factors aim to to implement enterprise applications in a modern way. Some of the principles sound obvious to most engineers, while others seem to contradict the common practice of building enterprise applications.

The list of the 12-factors includes:

• I. Have one codebase tracked in revision control, many deploys
• II. Explicitly declare and isolate dependencies
• III. Store config in the environment
• IV. Treat backing services as attached resources
• V. Strictly separate build and run stages
• VI. Execute the app as one or more stateless processes
• VII. Export services via port binding
• VIII. Scale out via the process model
• IX. Maximize robustness with fast startup and graceful shutdown
• X. Keep development, staging, and production as similar as possible
• XI. Treat logs as event streams
• XII. Run admin/management tasks as one-off processes

The following explains the motivations of each principle and its realization with Java EE.