NATS MessagingNATS

Pub/Sub: 발행-구독 (fire-and-forget)
  Publisher → [subject] → Subscriber(들)

Request/Reply: 동기 요청-응답
  Requester → [subject] → Responder → Reply

Queue Group: 부하 분산
  Publisher → [subject] → [Queue Group] → 하나의 Worker

JetStream: 영속 메시징 (Kafka 유사)
  Producer → Stream → Consumer (ack 필요)

package main

import (
    "fmt"
    "time"
    "github.com/nats-io/nats.go"
)

func main() {
    nc, _ := nats.Connect(nats.DefaultURL)
    defer nc.Drain()

    // Pub/Sub
    nc.Subscribe("orders.new", func(m *nats.Msg) {
        fmt.Printf("Received: %s
", string(m.Data))
    })
    nc.Publish("orders.new", []byte(`{"id":1001}`))

    // Request/Reply
    nc.Subscribe("calc.add", func(m *nats.Msg) {
        m.Respond([]byte("42"))
    })
    reply, _ := nc.Request("calc.add", []byte(`{"a":20,"b":22}`), time.Second)
    fmt.Println(string(reply.Data))

    // Queue Group (부하 분산)
    for i := 0; i < 3; i++ {
        nc.QueueSubscribe("tasks", "workers", func(m *nats.Msg) {
            fmt.Printf("Worker got: %s
", m.Data)
        })
    }

    // JetStream
    js, _ := nc.JetStream()
    js.AddStream(&nats.StreamConfig{
        Name:     "ORDERS",
        Subjects: []string{"orders.*"},
    })
    js.Publish("orders.created", []byte(`{"id":1002}`))

    sub, _ := js.Subscribe("orders.*", func(m *nats.Msg) {
        m.Ack()
    }, nats.Durable("order-processor"))
    defer sub.Unsubscribe()
}