The Twelve-Factor App is a methodology for building software-as-a-service applications that emphasizes best practices and principles for developing web applications. It provides a set of twelve guidelines aimed at maximizing application portability, scalability, and maintainability. The principles focus on aspects such as codebase management, dependencies, configuration, backing services, and process management, among others. By adhering to these factors, developers can create applications that are more robust, adaptable to changing environments, and easier to deploy and manage in a cloud-based ecosystem.

Key Points:

• Codebase: One codebase tracked in source control, multiple deployments.
• Dependencies: Explicitly declare and isolate dependencies.
• Configuration: Store configuration in the environment, separate from code.
• Backing Services: Treat backing services as attached resources, which can be swapped easily.
• Build, Release, Run: Strictly separate the build, release, and run stages.
• Processes: Execute the application as one or more stateless processes.
• Port Binding: Export services through 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 administrative/management tasks as one-off processes.
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