# Event-Driven Architecture Design

**Date**: 2025-01-27
**Purpose**: Design document for event-driven architecture integration
**Status**: Design Document

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## Executive Summary

This document outlines the design for implementing event-driven architecture across the workspace, enabling cross-project communication and real-time updates.

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## Architecture Overview

### Components

1. **Event Bus** (NATS, RabbitMQ, or Kafka)
2. **Event Producers** (Projects publishing events)
3. **Event Consumers** (Projects subscribing to events)
4. **Event Schemas** (Shared event definitions)
5. **Event Monitoring** (Observability and tracking)

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## Technology Options

### Option 1: NATS (Recommended)

**Pros**:
- Lightweight and fast
- Simple setup
- Good for microservices
- Built-in streaming (NATS JetStream)

**Cons**:
- Less mature than Kafka
- Limited enterprise features

### Option 2: RabbitMQ

**Pros**:
- Mature and stable
- Good management UI
- Flexible routing
- Good documentation

**Cons**:
- Higher resource usage
- More complex setup

### Option 3: Apache Kafka

**Pros**:
- High throughput
- Durable message storage
- Excellent for event streaming
- Enterprise features

**Cons**:
- Complex setup
- Higher resource requirements
- Steeper learning curve

**Recommendation**: Start with NATS for simplicity, migrate to Kafka if needed for scale.

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## Event Schema Design

### Event Structure

```typescript
interface BaseEvent {
  id: string;
  type: string;
  source: string;
  timestamp: Date;
  version: string;
  data: unknown;
  metadata?: Record<string, unknown>;
}
```

### Event Types

#### User Events
- `user.created`
- `user.updated`
- `user.deleted`
- `user.authenticated`

#### Transaction Events
- `transaction.created`
- `transaction.completed`
- `transaction.failed`
- `transaction.cancelled`

#### System Events
- `system.health.check`
- `system.maintenance.start`
- `system.maintenance.end`

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## Implementation Plan

### Phase 1: Event Bus Setup (Weeks 1-2)
- [ ] Deploy NATS/RabbitMQ/Kafka
- [ ] Configure clusters
- [ ] Set up authentication
- [ ] Configure monitoring

### Phase 2: Event Schemas (Weeks 3-4)
- [ ] Create shared event schemas package
- [ ] Define event types
- [ ] Create validation schemas
- [ ] Document event contracts

### Phase 3: Producer Implementation (Weeks 5-6)
- [ ] Implement event producers in projects
- [ ] Add event publishing utilities
- [ ] Test event publishing
- [ ] Monitor event flow

### Phase 4: Consumer Implementation (Weeks 7-8)
- [ ] Implement event consumers
- [ ] Add event handlers
- [ ] Test event processing
- [ ] Handle errors and retries

### Phase 5: Monitoring (Weeks 9-10)
- [ ] Set up event monitoring
- [ ] Create dashboards
- [ ] Set up alerts
- [ ] Track event metrics

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## Event Patterns

### Publish-Subscribe
- Multiple consumers per event
- Decoupled producers and consumers
- Use for notifications

### Request-Reply
- Synchronous communication
- Response required
- Use for RPC-like calls

### Event Sourcing
- Store all events
- Replay events for state
- Use for audit trails

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## Security

### Authentication
- Use TLS for connections
- Authenticate producers/consumers
- Use service accounts

### Authorization
- Topic-based permissions
- Limit producer/consumer access
- Audit event access

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## Monitoring

### Metrics
- Event publish rate
- Event consumption rate
- Processing latency
- Error rates
- Queue depths

### Alerts
- High error rate
- Slow processing
- Queue buildup
- Connection failures

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## Best Practices

### Event Design
- Keep events small
- Use versioning
- Include correlation IDs
- Make events idempotent

### Error Handling
- Retry with backoff
- Dead letter queues
- Log all errors
- Alert on failures

### Performance
- Batch events when possible
- Use compression
- Monitor throughput
- Scale horizontally

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## Migration Strategy

### Gradual Migration
1. Deploy event bus
2. Migrate one project as pilot
3. Add more projects gradually
4. Monitor and optimize

### Coexistence
- Support both sync and async
- Gradual migration
- No breaking changes
- Rollback capability

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**Last Updated**: 2025-01-27