2nd/10_Wiki/Topics/Domain_Programming/Architecture/Simple event processing.md

id, title, category, status, canonical_id, aliases, duplicate_of, source_trust_level, confidence_score, verification_status, tags, raw_sources, last_reinforced, github_commit, tech_stack

id	title	category	status	canonical_id	aliases	duplicate_of	source_trust_level	confidence_score	verification_status	tags	raw_sources	last_reinforced	github_commit	tech_stack
wiki-2026-0508-simple-event-processing	Simple Event Processing	10_Wiki/Topics	verified	self	SEP Direct Event Handling 1:1 Event Processing	none	A	0.9	applied	event-driven architecture eda messaging		2026-05-10	pending	language framework typescript kafka

Simple Event Processing

매 한 줄

"매 1 event → 1 reaction. No correlation, no aggregation, no temporal pattern.". 매 EDA 의 simplest tier — notable event 의 detect 후 매 single downstream action 의 trigger. 매 CEP (Complex Event Processing) / ESP (Event Stream Processing) 와 대비되는 매 baseline pattern.

매 핵심

매 SEP vs ESP vs CEP

• SEP: 1 event → 1 action. No state, no correlation.
• ESP: stream 의 windowing, aggregation (Flink, Kafka Streams).
• CEP: pattern matching across events (Drools Fusion, Esper).

매 properties

• Stateless (매 event 의 self-contained).
• Low latency (no buffering / windowing).
• High throughput (parallelize trivially).
• Idempotent handlers preferred (at-least-once delivery).

매 응용

1. Order placed → email confirmation.
2. User signup → welcome workflow.
3. Sensor reading → threshold alert.
4. Payment captured → inventory reserve.
5. Log line → metric increment.

💻 패턴

Kafka consumer (TypeScript)

import { Kafka } from 'kafkajs';

const kafka = new Kafka({ brokers: ['localhost:9092'] });
const consumer = kafka.consumer({ groupId: 'order-emails' });

await consumer.subscribe({ topic: 'orders.placed' });
await consumer.run({
  eachMessage: async ({ message }) => {
    const order = JSON.parse(message.value!.toString());
    await sendOrderEmail(order.userId, order.id);
  },
});

AWS EventBridge rule

import { EventBridgeClient, PutRuleCommand } from '@aws-sdk/client-eventbridge';

await client.send(new PutRuleCommand({
  Name: 'order-placed-email',
  EventPattern: JSON.stringify({
    source: ['app.orders'],
    'detail-type': ['OrderPlaced'],
  }),
  Targets: [{ Arn: lambdaArn, Id: 'send-email' }],
}));

NATS subject handler

import { connect, StringCodec } from 'nats';

const nc = await connect({ servers: 'nats://localhost:4222' });
const sc = StringCodec();
const sub = nc.subscribe('orders.placed');

for await (const msg of sub) {
  const order = JSON.parse(sc.decode(msg.data));
  await reserveInventory(order);
}

Idempotent handler

async function handleOrderPlaced(event: OrderEvent) {
  const seen = await redis.set(`processed:${event.id}`, '1', 'NX', 'EX', 86400);
  if (!seen) return;  // already handled
  await sendEmail(event);
}

Dead-letter handling

await consumer.run({
  eachMessage: async ({ message }) => {
    try {
      await handle(message);
    } catch (err) {
      await producer.send({
        topic: 'orders.placed.dlq',
        messages: [{ value: message.value, headers: { error: err.message } }],
      });
    }
  },
});

CloudEvents envelope

const cloudEvent = {
  specversion: '1.0',
  type: 'com.example.order.placed',
  source: '/orders',
  id: crypto.randomUUID(),
  time: new Date().toISOString(),
  data: { orderId, userId, amount },
};
await producer.send({ topic: 'orders.placed', messages: [{ value: JSON.stringify(cloudEvent) }] });

Webhook fan-out

app.post('/webhooks/payment', async (req, res) => {
  await eventBus.publish('payment.captured', req.body);
  res.status(202).end();
});

매 결정 기준

상황	Approach
1:1 event → action, stateless	SEP
Stream aggregation (window sums)	ESP (Flink)
Pattern detect (A then B within 5s)	CEP (Esper)
Cross-system fan-out	SEP via EventBridge/Kafka

기본값: Kafka or EventBridge + idempotent stateless handlers.

🔗 Graph

• 부모: Event-Driven-Architecture
• 변형: Event Stream Processing
• 응용: Webhooks · Pub-Sub · Event Sourcing
• Adjacent: CQRS

🤖 LLM 활용

언제: stateless 1:1 event handling — webhook, notification, simple workflow trigger. 언제 X: pattern correlation 필요 — CEP / ESP 사용.

❌ 안티패턴

• Stateful SEP: 매 cross-event state 가지면 ESP 로 reframe.
• No idempotency: at-least-once delivery 에서 매 duplicate side-effect.
• Synchronous webhook chain: 매 cascading failure — async queue 사이로.

🧪 검증 / 중복

• Verified (Hohpe Enterprise Integration Patterns, Confluent docs, AWS EventBridge guide).
• 신뢰도 A.

🕓 Changelog

날짜	변경
2026-05-08	Phase 1
2026-05-10	Manual cleanup — SEP vs ESP vs CEP, Kafka/EventBridge/NATS patterns