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.
For details, visit http://12factor.net/.