Your product and the deployment

Your hosted application owns accounts, billing, product-wide state, and the user experience. A deployment owns the code and resources that need another environment.

Commands, HTTP, events, and bindings connect them. Choose the interface from the work you need to do, then document the inputs, results, logs, and telemetry that cross it.

hosted product                  deployment
accounts · billing             private code · resources
       │                              │
       └── commands · HTTP · events ──┘
                  · bindings

See How Alien works and What data moves?.