2nd/10_Wiki/Topics/AI_and_ML/Event-Driven-Architecture.md

---
id: wiki-2026-0508-event-driven-architecture
title: Event-Driven Architecture
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [EDA, event-driven, pub-sub, message-driven, choreography, orchestration]
duplicate_of: none
source_trust_level: A
confidence_score: 0.97
verification_status: applied
tags: [architecture, eda, event-driven, kafka, pub-sub, choreography, microservices]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: TypeScript / Java / Python
  framework: Kafka / RabbitMQ / EventBridge / NATS
---

# Event-Driven Architecture

## 매 한 줄
> **"매 service 의 event 의 의 communicate"**. 매 sync HTTP RPC 의 X — 매 async pub/sub. 매 decouple + scale + replay. 매 modern: 매 Kafka, EventBridge, NATS, async.

## 매 핵심

### 매 pattern
- **Event notification**: 매 fire-and-forget.
- **Event-carried state transfer**: 매 payload 의 state.
- **Event sourcing**: 매 store events.
- **CQRS**: 매 read/write split.

### 매 choreography vs orchestration
- **Choreography**: 매 service 의 react.
- **Orchestration**: 매 central coordinator (saga).

### 매 응용
1. **Microservices**: 매 decouple.
2. **Real-time**: 매 streaming.
3. **Fan-out**: 매 1 → many.
4. **Audit**: 매 replay.
5. **Integration**: 매 cross-system.

## 💻 패턴

### Kafka producer (Java)
```java
KafkaProducer<String, String> p = new KafkaProducer<>(props);
p.send(new ProducerRecord<>("orders.placed", orderId, json), (md, ex) -> {
    if (ex != null) log.error("Failed", ex);
});
```

### Kafka consumer (Python)
```python
from confluent_kafka import Consumer
c = Consumer({'bootstrap.servers': 'kafka:9092', 'group.id': 'inventory', 'auto.offset.reset': 'earliest'})
c.subscribe(['orders.placed'])
while True:
    msg = c.poll(1.0)
    if msg and not msg.error():
        handle_order(json.loads(msg.value()))
```

### Outbox (transactional publish)
```typescript
async function placeOrder(o: Order) {
  await db.transaction(async tx => {
    await tx.orders.save(o);
    await tx.outbox.insert({ topic: 'orders.placed', payload: o, status: 'pending' });
  });
}
// 매 separate process polls outbox → Kafka
```

### Schema registry (Avro)
```json
{
  "type": "record",
  "name": "OrderPlaced",
  "fields": [
    { "name": "orderId", "type": "string" },
    { "name": "amount", "type": "long" },
    { "name": "currency", "type": "string", "default": "USD" }
  ]
}
```

### Saga orchestration
```typescript
class OrderSaga {
  async execute(orderId: string) {
    try {
      await reservePayment(orderId);
      await reserveInventory(orderId);
      await scheduleShipping(orderId);
    } catch (e) {
      await this.compensate(orderId);
      throw e;
    }
  }
  
  async compensate(orderId: string) {
    await releaseInventory(orderId);
    await refundPayment(orderId);
  }
}
```

### Choreography (each service reacts)
```typescript
// 매 inventory service
on('orders.placed', async event => {
  const ok = await reserve(event.orderId);
  publish(ok ? 'inventory.reserved' : 'inventory.failed', event);
});

// 매 shipping service
on('inventory.reserved', async event => {
  await schedule(event.orderId);
  publish('shipping.scheduled', event);
});
```

### DLQ (dead letter queue)
```python
def consume_with_dlq(topic, handler, max_retries=3):
    for msg in consumer:
        for attempt in range(max_retries):
            try:
                handler(msg)
                break
            except Exception as e:
                if attempt == max_retries - 1:
                    dlq.publish(msg, error=str(e))
```

### Idempotency
```python
def idempotent_handler(event):
    if redis.set(f'evt:{event.id}', '1', nx=True, ex=86400):
        process(event)
    # 매 else: skip duplicate
```

### Backpressure
```python
def consume_with_backpressure(consumer, max_in_flight=100):
    sem = Semaphore(max_in_flight)
    for msg in consumer:
        sem.acquire()
        thread = Thread(target=lambda m=msg: (process(m), sem.release()))
        thread.start()
```

### Event versioning
```typescript
type OrderPlacedV1 = { version: 1; orderId: string; amount: number };
type OrderPlacedV2 = { version: 2; orderId: string; amount: number; currency: string };

function migrate(e: OrderPlacedV1 | OrderPlacedV2): OrderPlacedV2 {
  if (e.version === 1) return { ...e, version: 2, currency: 'USD' };
  return e;
}
```

## 매 결정 기준
| 상황 | Tool |
|---|---|
| High throughput | Kafka |
| Cloud-native AWS | EventBridge / SNS+SQS |
| Low latency | NATS |
| Complex routing | RabbitMQ |
| Simple pub/sub | Redis Streams |
| Multi-step | Saga (Temporal) |

**기본값**: 매 Kafka + 매 schema registry + 매 outbox + 매 DLQ + 매 idempotency.

## 🔗 Graph
- 부모: [[Architecture]] · [[Distributed-Systems]]
- 변형: [[Event Sourcing Pattern]] · [[CQRS]]
- 응용: [[Kafka]] · [[NATS]]
- Adjacent: [[Microservices]]

## 🤖 LLM 활용
**언제**: 매 microservice. 매 streaming. 매 decouple.
**언제 X**: 매 simple monolith. 매 strict transaction.

## ❌ 안티패턴
- **Sync inside async**: 매 backpressure 의 break.
- **No schema**: 매 break.
- **No DLQ**: 매 stuck consumer.
- **No idempotency**: 매 duplicate processing.
- **Choreography 의 over-use**: 매 spaghetti.

## 🧪 검증 / 중복
- Verified (Fowler EDA, Confluent, AWS Reference Architecture).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-04-20 | Auto-reinforced |
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — EDA + 매 Kafka / outbox / saga / DLQ / idempotency code |