retellai-architecture-variants

# Retell AI Architecture Variants

## Overview
Three validated architecture blueprints for Retell AI integrations.

## Prerequisites
- Understanding of team size and DAU requirements
- Knowledge of deployment infrastructure
- Clear SLA requirements
- Growth projections available

## Variant A: Monolith (Simple)

**Best for:** MVPs, small teams, < 10K daily active users

```
my-app/
├── src/
│   ├── retellai/
│   │   ├── client.ts          # Singleton client
│   │   ├── types.ts           # Types
│   │   └── middleware.ts      # Express middleware
│   ├── routes/
│   │   └── api/
│   │       └── retellai.ts    # API routes
│   └── index.ts
├── tests/
│   └── retellai.test.ts
└── package.json
```

### Key Characteristics
- Single deployment unit
- Synchronous Retell AI calls in request path
- In-memory caching
- Simple error handling

### Code Pattern
```typescript
// Direct integration in route handler
app.post('/api/create', async (req, res) => {
  try {
    const result = await retellaiClient.create(req.body);
    res.json(result);
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});
```

---

## Variant B: Service Layer (Moderate)

**Best for:** Growing startups, 10K-100K DAU, multiple integrations

```
my-app/
├── src/
│   ├── services/
│   │   ├── retellai/
│   │   │   ├── client.ts      # Client wrapper
│   │   │   ├── service.ts     # Business logic
│   │   │   ├── repository.ts  # Data access
│   │   │   └── types.ts
│   │   └── index.ts           # Service exports
│   ├── controllers/
│   │   └── retellai.ts
│   ├── routes/
│   ├── middleware/
│   ├── queue/
│   │   └── retellai-processor.ts  # Async processing
│   └── index.ts
├── config/
│   └── retellai/
└── package.json
```

### Key Characteristics
- Separation of concerns
- Background job processing
- Redis caching
- Circuit breaker pattern
- Structured error handling

### Code Pattern
```typescript
// Service layer abstraction
class Retell AIService {
  constructor(
    priva