---
id: ADR-0009
type: ADR
title: "Rate Limiting Strategy"
status: Accepted
decision_date: 2026-01-10
updated_at: 2026-01-10
simco_version: "4.0.1"
stakeholders:
  - "Equipo MiChangarrito"
tags:
  - rate-limiting
  - api
  - redis
  - security
---

# ADR-0009: Rate Limiting Strategy

## Metadata

| Campo | Valor |
|-------|-------|
| **ID** | ADR-0009 |
| **Estado** | Accepted |
| **Fecha** | 2026-01-10 |
| **Autor** | Architecture Team |
| **Supersede** | - |

---

## Contexto

MiChangarrito expone una API REST que puede ser abusada por clientes mal configurados o ataques maliciosos. Necesitamos rate limiting para:

1. Proteger la infraestructura
2. Garantizar uso justo entre tenants
3. Diferenciar limites por plan
4. Informar a clientes sobre limites

---

## Decision

**Implementamos Token Bucket algorithm con Redis, limites por plan/tenant y headers estandar de rate limit.**

```
Header: X-RateLimit-Limit: 1000
Header: X-RateLimit-Remaining: 999
Header: X-RateLimit-Reset: 1704880800
```

---

## Alternativas Consideradas

### Opcion 1: Fixed Window
- **Pros:**
  - Simple de implementar
  - Facil de entender
- **Cons:**
  - Vulnerable a bursts al cambiar ventana
  - No es smooth

### Opcion 2: Sliding Window Log
- **Pros:**
  - Preciso
  - Sin bursts
- **Cons:**
  - Alto uso de memoria
  - Queries complejas

### Opcion 3: Token Bucket (Elegida)
- **Pros:**
  - Permite bursts controlados
  - Eficiente en memoria
  - Smooth rate limiting
- **Cons:**
  - Ligeramente mas complejo

---

## Consecuencias

### Positivas

1. **Proteccion:** API protegida contra abusos
2. **Justicia:** Cada tenant tiene su cuota
3. **Transparencia:** Headers informan estado
4. **Flexibilidad:** Limites por plan

### Negativas

1. **Dependencia Redis:** Requiere Redis disponible
2. **Complejidad:** Logica adicional en cada request

---

## Implementacion

### Limites por Plan

| Plan | Requests/minuto | Requests/dia | Burst |
|------|-----------------|--------------|-------|
| Basic | 60 | 10,000 | 10 |
| Pro | 300 | 100,000 | 50 |
| Enterprise | 1,000 | 1,000,000 | 100 |

### Guard

```typescript
@Injectable()
export class RateLimitGuard implements CanActivate {
  constructor(
    @Inject('REDIS_CLIENT') private readonly redis: Redis,
    private readonly planService: PlanService,
  ) {}

  async canActivate(context: ExecutionContext): Promise<boolean> {
    const request = context.switchToHttp().getRequest();
    const response = context.switchToHttp().getResponse();
    const tenantId = request.user?.tenantId;

    if (!tenantId) return true; // Sin tenant, skip

    const plan = await this.planService.getTenantPlan(tenantId);
    const limit = this.getLimitForPlan(plan);

    const result = await this.checkLimit(tenantId, limit);

    // Agregar headers
    response.setHeader('X-RateLimit-Limit', limit.requestsPerMinute);
    response.setHeader('X-RateLimit-Remaining', result.remaining);
    response.setHeader('X-RateLimit-Reset', result.resetAt);

    if (!result.allowed) {
      response.setHeader('Retry-After', result.retryAfter);
      throw new HttpException({
        statusCode: 429,
        message: 'Too Many Requests',
        retryAfter: result.retryAfter,
      }, 429);
    }

    return true;
  }

  private async checkLimit(
    tenantId: string,
    limit: RateLimit,
  ): Promise<RateLimitResult> {
    const key = `rate:${tenantId}`;
    const now = Date.now();
    const windowMs = 60 * 1000; // 1 minuto

    const pipe = this.redis.pipeline();

    // Remover tokens viejos
    pipe.zremrangebyscore(key, 0, now - windowMs);

    // Contar tokens actuales
    pipe.zcard(key);

    // Agregar token actual
    pipe.zadd(key, now, `${now}-${Math.random()}`);

    // Expirar key
    pipe.expire(key, 60);

    const results = await pipe.exec();
    const count = results[1][1] as number;

    const allowed = count < limit.requestsPerMinute;
    const remaining = Math.max(0, limit.requestsPerMinute - count - 1);
    const resetAt = Math.floor((now + windowMs) / 1000);

    return {
      allowed,
      remaining,
      resetAt,
      retryAfter: allowed ? 0 : Math.ceil(windowMs / 1000),
    };
  }
}
```

### Bypass

Algunas rutas no tienen rate limit:

```typescript
@RateLimitBypass()
@Get('health')
healthCheck() {
  return { status: 'ok' };
}

// Decorator
export const RateLimitBypass = () => SetMetadata('rateLimitBypass', true);
```

### Response 429

```json
{
  "statusCode": 429,
  "message": "Too Many Requests",
  "error": "Rate limit exceeded. Please retry after 45 seconds.",
  "retryAfter": 45
}
```

---

## Headers Estandar

| Header | Descripcion |
|--------|-------------|
| `X-RateLimit-Limit` | Limite maximo de requests |
| `X-RateLimit-Remaining` | Requests restantes |
| `X-RateLimit-Reset` | Unix timestamp cuando se resetea |
| `Retry-After` | Segundos a esperar (solo en 429) |

---

## Monitoreo

### Metricas

```typescript
rate_limit_requests_total{tenant, plan, allowed}
rate_limit_exceeded_total{tenant, plan}
```

### Alertas

- Rate limit hits > 100/minuto por tenant
- Mismo IP excediendo multiples tenants

---

## Referencias

- [Token Bucket Algorithm](https://en.wikipedia.org/wiki/Token_bucket)
- [RFC 6585 - 429 Too Many Requests](https://tools.ietf.org/html/rfc6585)
- [GitHub API Rate Limiting](https://docs.github.com/en/rest/rate-limit)

---

**Fecha decision:** 2026-01-10
**Autores:** Architecture Team