Modules and application composition

Arqen uses explicit modules to make application wiring visible. A module owns its routes, tools, jobs, health checks, and lifecycle hooks. It does not use a hidden dependency-injection container or global service locator.

The composition model

ModuleBuilder
  ├─ dependencies()  → dependency graph
  ├─ register()      → routes, tools, jobs, checks
  ├─ init()          → startup lifecycle
  └─ shutdown()      → graceful teardown

Implement Module for a feature boundary and add it to ModuleBuilder. Dependencies are declared by module name and initialized in dependency order. ModuleGraphError and ModuleError report invalid graphs and registration failures without hiding the cause.

use arqen::{Module, ModuleBuilder};

let builder = ModuleBuilder::new()
    .add_module(MyAccountsModule)
    .add_module(MyJobsModule);

ArqenApp runs registration, initialization, serving, and best-effort shutdown. Use ModuleContext to register health checks and other public application capabilities. Keep domain services in your application and pass them through explicit AppState rather than relying on implicit resolution.

When to use a module

Create a module when a feature has more than one boundary—such as routes plus a job worker, or tools plus a dependency health check. A small application can start with one module and split it later. HttpModule is available for route- focused composition.

See testing for composing modules in an in-process test app.