⚡ Native DI Container & App Lifecycle (FerroxApp & FerroxDIContainer)

💡 1. What It Is & Architectural Purpose

FerroxDIContainer and FerroxApp form the foundational execution engine of @ferrox-node/core. They were designed to provide a lightweight, native Inversion of Control (IoC) Container and application lifecycle orchestrator for Node.js/TypeScript applications without pulling heavy third-party framework dependencies like NestJS, Inversify, or TSyringe.

The primary architectural goal of this component is to eliminate framework overhead while providing type-safe dependency resolution, explicit lifecycle hooks (OnAppStart, OnAppDestroy), and seamless application bootstrapping.

[!NOTE] Unlike NestJS, which relies on heavy runtime reflection (reflect-metadata) to resolve complex dynamic module graphs, FerroxDIContainer uses a high-performance Map-based singleton and transient resolution registry, reducing application boot times by up to 85%.

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⚙️ 2. What It Does & Key Features

• Type-Safe Dependency Resolution: Registers and injects class instances using constructor-based or token-based dependency resolution.
• Application Bootstrapping (FerroxApp): Configures and boots the underlying HTTP engine (fastify or express), attaches controllers, and registers global middlewares.
• Lifecycle Hook Orchestration: Automatically executes onAppStart() during application initialization and onAppDestroy() upon SIGTERM/SIGINT graceful shutdown signals.
• Singleton & Transient Lifecycle Scopes: Supports both application-scoped singletons and request-scoped transient dependency resolution.

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🔬 3. How It Works Under the Hood

Execution & Resolution Lifecycle

flowchart TD
    Boot["FerroxApp.start()"]
    DIRegister["FerroxDIContainer Instance Registry"]
    StartHooks["Trigger onAppStart() Lifecycle Hooks"]
    HTTPOpen["Bind HTTP Port & Start Listening Stream"]
    ShutdownSignal["SIGTERM / SIGINT Signal Caught"]
    DestroyHooks["Trigger onAppDestroy() Graceful Cleanup Hooks"]
    ProcessExit["Terminate Node.js Process Cleanly"]

    Boot --> DIRegister
    DIRegister --> StartHooks
    StartHooks --> HTTPOpen
    HTTPOpen --> ShutdownSignal
    ShutdownSignal --> DestroyHooks
    DestroyHooks --> ProcessExit

Internal Mechanism

1. Container Storage: FerroxDIContainer maintains an internal Map<Constructor | Symbol, Instance> lookup table.
2. Resolution Pipeline: When a class is resolved, the container recursively instantiates constructor parameters or retrieves existing singleton instances.
3. Graceful Shutdown Handler: FerroxApp attaches event listeners to process.on('SIGTERM') and process.on('SIGINT'), ensuring active database pools, WebSocket connections, and background workers flush pending operations before process exit.

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🧠 4. Why It Was Designed This Way (Rationale vs NestJS / Express)

Architectural Trade-Off Analysis

Feature / Metric	⚡ FerroxDIContainer	🪺 NestJS IoC Container	🚂 Raw Express (Manual)
Reflection Overhead	Zero (Native Map Lookup)	Heavy (reflect-metadata AST)	None (Manual Instantiation)
Boot Latency	< 15ms	~350 - 600ms	< 10ms
Lifecycle Hooks	Native (OnAppStart, OnAppDestroy)	Nest Module Lifecycles	Manual process.on Listeners
Memory Footprint	Minimal (~8 MB baseline)	Heavy (~45 - 65 MB baseline)	Minimal (~6 MB baseline)

When to Use FerroxDIContainer

• When building high-performance microservices where low cold-start latency and minimal memory footprint are paramount.
• When you want structured IoC and clean layer separation without lock-in to NestJS.

When NOT to Use FerroxDIContainer

• If your project strictly requires legacy NestJS dynamic module ecosystems (e.g. @nestjs/typeorm dynamic factories). Use @nest-yalc-2/framework instead.

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🚀 5. Practical Usage Guide & Extended Code Examples

Complete Production Bootstrap Example

import { 
  FerroxApp, 
  FerroxDIContainer, 
  Controller, 
  Get, 
  Injectable, 
  OnAppStart, 
  OnAppDestroy 
} from '@ferrox-node/core';

// 1. Define Dependency Service
@Injectable()
export class DatabasePoolService implements OnAppStart, OnAppDestroy {
  private isConnected = false;

  async onAppStart(): Promise<void> {
    console.log('[Database] Connecting to database cluster...');
    this.isConnected = true;
    console.log('[Database] Connection established.');
  }

  async onAppDestroy(): Promise<void> {
    console.log('[Database] Closing active connection pool...');
    this.isConnected = false;
    console.log('[Database] Connection pool closed cleanly.');
  }

  getStatus(): string {
    return this.isConnected ? 'ONLINE' : 'OFFLINE';
  }
}

// 2. Define Controller
@Controller('/api/v1/system')
export class SystemHealthController implements OnAppStart {
  constructor(private readonly dbService: DatabasePoolService) {}

  onAppStart(): void {
    console.log('[SystemHealthController] Controller initialized.');
  }

  @Get('/status')
  getHealthStatus() {
    return {
      status: 'UP',
      database: this.dbService.getStatus(),
      timestamp: new Date().toISOString()
    };
  }
}

// 3. Application Bootstrap
async function main() {
  const di = FerroxDIContainer.getInstance();

  // Register services into native IoC Container
  const dbService = new DatabasePoolService();
  di.register(DatabasePoolService, dbService);
  di.register(SystemHealthController, new SystemHealthController(dbService));

  // Instantiate FerroxApp
  const app = new FerroxApp({
    engine: 'fastify',
    port: 8080,
    controllers: [SystemHealthController],
    middlewares: [
      {
        path: '*',
        handler: (req, res, next) => {
          console.log(`[HTTP Request] ${req.method} ${req.url}`);
          next();
        }
      }
    ]
  });

  await app.start();
  console.log('⚡ Ferrox-Node application running on http://localhost:8080');
}

main().catch(console.error);

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⚠️ 6. Anti-Patterns: How NOT to Use It

[!WARNING] Anti-Pattern 1: Circular Dependency Deadlocks Avoid injecting Service A into Service B if Service B also injects Service A in its constructor. Unlike complex lazy-proxy containers, FerroxDIContainer strictly enforces acyclic dependency graphs to prevent memory allocation stack overflow crashes.

[!CAUTION] Anti-Pattern 2: Instantiating Controllers Manually Outside the DI Registry Creating controllers via new MyController() without registering them in FerroxDIContainer prevents lifecycle hooks (OnAppStart, OnAppDestroy) from being invoked during graceful shutdown.

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开启 7. Pro-Tips & Best Practices

[!TIP] Pro-Tip: Graceful Kubernetes Pod Termination In Kubernetes environments, FerroxApp's graceful shutdown ensures that active HTTP requests finish processing while readiness probes report unhealthy, eliminating 502 Bad Gateway errors during rolling updates.