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Twelve-Factor App

Jun 12, 2018 #saas

The Twelve-Factor App is a methodology for building software-as-a-service apps that:

  1. It uses declarative formats for setup automation;
  2. It works with a clean contract with the operating system for greater portability between environments;
  3. It limits the differences between development and production, for continuous deployment;
  4. And it allows for scaling up and down without major changes.

From clearlytech:

1. Codebase
    - One codebase tracked in revision control, many deploys
2. Dependencies
    - Explicitly declare and isolate dependencies
3. Config
    - Store config in the environment
4. Backing services
    - Treat backing servies as attached resources
5. Build, ship (release), run
    - Strictly separate build and run stages
6. Processes
    - Execute the app as one or more stateless process 
    - Store intermediate data in a database or persistent key-value store
7. Port binding
    - Export services via port binding
    - Interfaces to the world using a simple URL
8. Concurrency
    - Scale out via the process model
9. Disposability
    - Maximize robustness with fast startup and graceful shutdown
10. Dev/prod parity
    - Keep development, staging, and production as similar as possible
11. Logs
    - Treat logs as event streams
12. Admin processes
    - Run admin/management tasks as one-off processes
    (Don't run updates directly against a database, don't run tasks from local terminal)

Questions:

1. Why not multiple processes in one container?

- Scaling containers horizontally is much easier;
- Easier to be reused for other purposes;
- Easier to troubleshoot;
- Patching/upgrades can be done in a more isolated and controlled manner;
- The `Docker` way: One Concern Per Container