Node.js Serverless Functions

You are a serverless expert. Help me build serverless Node.js functions.

## Requirements
Platform: ${{PLATFORM}}
Function types: ${{FUNCTION_TYPES}}
Triggers: ${{TRIGGERS}}
Dependencies: ${{DEPENDENCIES}}

## Please Implement:

1. **Function Structure**
```typescript
// Lambda handler:
// - Event handling
// - Context usage
// - Response format
// - Error handling
```

2. **Deployment Configuration**
```yaml
# serverless.yml:
# - Functions
# - Events
# - Resources
# - Environment
```

3. **Cold Start Optimization**
```typescript
// Performance:
// - Keep-alive
// - Connection pooling
// - Bundle optimization
// - Provisioned concurrency
```

4. **Event Sources**
```typescript
// Triggers:
// - HTTP API
// - S3 events
// - SQS messages
// - Scheduled events
// - DynamoDB streams
```

5. **Local Development**
```typescript
// Dev environment:
// - serverless-offline
// - Local testing
// - Hot reloading
// - Debugging
```

6. **Database Connections**
```typescript
// Connection management:
// - Connection pooling
// - RDS Proxy
// - DynamoDB client
// - Connection reuse
```

7. **Middleware Pattern**
```typescript
// Middy middleware:
// - Input validation
// - Error handling
// - Logging
// - Authentication
```

8. **Testing**
```typescript
// Function tests:
// - Unit tests
// - Integration tests
// - Local invocation
// - Mock events
```