[Microservices] Twelve-Factor App Methology

Modern software development

• Delivery as a service 
• Centrally hosted and accessed through the internet
• Web apps, software-as-a-service
• Twelve-factor app methodology is suited for web apps

Code -> Deploy -> Operate

 

Factor 1: Codebase: Code factor

Track in a version control system(VCS)

• Maintain one-to-one relationship between codebase and app
• Deploy multiple instances of the app
• Develop differnetversions of the codebase in each deploy

Factor 2: Dependencies:Code factor.

• Assume an app is only as reliable as its least reliable dependency
• Explicitly declare any dependencies

Factor 3: Config: Deploy factors

• Keep everythng that varies between deploys such as credentials and backend service locations in config
• Keep separate from the code
• Store config in environment variables

Factor 4: Backend services: Deploy factor.

• Do not distinguish between local and third-part services
• Access all services by a URL and credentials so that they can be swapped without changing the code

Factor 5: Build, release , run: Code factor

• Build: Transform a code base into an executable unit called a build
• Release: Combine build with configuration so that it;s ready for execution
• Run: Run the application

Factor 6: Processes: Deploy factor.

• Should be stateless and share nothing
• Do not share memory and filesystmes so persistent data stored in backend service
• Store data centally

Factor 7: Port binding:Deploy factor.

• Export services by port binding.
• Export HTTP and other services.
• Declare a web server library dependency
• Become backend services for other apps

Factor 8: Concurrency: Operate factors.

• Scale an application
• Stateless processes can be spun up without createing dependencies on other processes

Factor 9: Disposability: Operate factors.

• Require minimal process start time and graceful termination
• Quickly deply code or config changes
• Easily scale apps

Factor 10: Dev/prod parity: Code factor.

• Minimize differences between development and production environments
• Use same backend services across environments

Factor 11: Logs: Operate factors.

• App should not concern itself with storing logs
• Threat logs as an event stream
• Execution environment captures, aggregates, and routes logs to their destination

Factor 12: Admin processes

• Enable one-off app management processes
• Run against a release, using same codebase and config
• Part of application code