FusionApplication lifecycle
What happens from process start to FusionApp.listen
What
The application lifecycle is the ordered sequence of steps from starting your process to serving HTTP traffic.
Startup sequence
flowchart TD
A[Process start] --> B[Import route modules]
B --> C[Route classes register with binding]
C --> D[load_settings_module / EnsureLoaded]
D --> E[FusionApp constructed]
E --> F[Optional app.use middleware]
F --> G[listen / Listen]
G --> H[Mount routes on Hyper]
H --> I[Mount Swagger if enabled]
I --> J[Accept connections]Step details
| Step | What happens |
|---|---|
| Import / register | Python/Node: decorators run at import. C#: Route.Register<T>() |
| Settings | Load fusion.<env>.json (FUSION_ENV, default dev). Python may merge UPPERCASE attrs from settings / core.settings |
FusionApp | Holds settings, middleware list, native engine handle |
| Middleware | Global chain prepared (see binding notes on framework_headers) |
listen | Binding mounts registered routes, optional Swagger routes, binds host/port, blocks serving |
Settings flow
flowchart LR
Env[FUSION_ENV] --> File["fusion.<env>.json"]
File --> Core[fusion-core Settings]
Py[Python settings.py UPPERCASE] --> Core
Core --> App[FusionApp host/port/swagger/fingerprint]If the JSON has a top-level config object (CLI scaffold style), that object is merged as settings. Otherwise top-level keys (except env / commands) are merged.
Shutdown
listen() typically blocks until the process is terminated. There is no separate Fusion “graceful shutdown API” documented beyond normal process signals — treat OS signal handling as application responsibility unless your binding exposes dispose/using patterns (C# FusionApp is IDisposable).
Next
- Settings and configuration —
fusion.<env>.json,FUSION_ENV, overlays - Request lifecycle
- Language Config: Python · TypeScript · C#