자꾸 까먹어서 정리하는 NatsIO - python

0. Intro 

빨리 NATs io 서버 띄우고 다른거 진행해야 하는데 자꾸 보다가 다른거 하다가 돌아오면 까먹는다. 그래서 진행이 안 되고 있다.

후딱 정리하고 다음으로 넘어가야겠다. 역시 일 하는 중 쓰는 블로그 효율이 제일 좋다.

 

이 글은 그냥 제가 후딱 보려고 대충 적었습니다. 참고가 안 될 것 으로 생각됩니다.

레퍼런스 좋아요. 그쪽 링크로 들어가서 보세요.

1. What is Nats? - Features

• Open source cloud native messaging system
• Performance, simplicity, security and availability
• Multple communication patterns
• completely distributed platform
• wild card subscribers
• fanout 
• load balanced
• request/reply
• publish/subscribe
• selfish optimization - protect against slow consumer
• self healing server-client connections -dial tone
• publisher rate limiting
• streams

2. Delivery modes

• At most once (Core) (NATS server / NATS)
• At least once (NATS streaming & Jet stream)

3. NATS in Docker

• docker image from docker hub
  • image name => nats
  • docker run --name nats --rm -p 4222:4222 nats
• with using telnet localhost 4222, you can easily publish messages
  • pub ${subject_name} ${length_of_message}
  • pub com.test 5 => publish subject name "com.test" and the message length is 5
  • hello => the message "hello" which the length is 5
  • you should see "+OK"
  • make sure the docker container is running
• nats client
  • pip install nats.py **

import asyncio
import nats
from nats.errors import ConnectionClosedError, TimeoutError, NoServersError

async def main():
    # It is very likely that the demo server will see traffic from clients other than yours.
    # To avoid this, start your own locally and modify the example to use it.
    nc = await nats.connect("nats://demo.nats.io:4222")

    # You can also use the following for TLS against the demo server.
    #
    # nc = await nats.connect("tls://demo.nats.io:4443")

    async def message_handler(msg):
        subject = msg.subject
        reply = msg.reply
        data = msg.data.decode()
        print("Received a message on '{subject} {reply}': {data}".format(
            subject=subject, reply=reply, data=data))

    # Simple publisher and async subscriber via coroutine.
    sub = await nc.subscribe("foo", cb=message_handler)

    # Stop receiving after 2 messages.
    # 위에서 command line 에서 pub 했던것과 같습니다
    await sub.unsubscribe(limit=2)
    await nc.publish("foo", b'Hello')
    await nc.publish("foo", b'World')
    await nc.publish("foo", b'!!!!!')

    # Synchronous style with iterator also supported.
    sub = await nc.subscribe("bar")
    await nc.publish("bar", b'First')
    await nc.publish("bar", b'Second')

    try:
        async for msg in sub.messages:
            print(f"Received a message on '{msg.subject} {msg.reply}': {msg.data.decode()}")
            await sub.unsubscribe()
    except Exception as e:
        pass

    async def help_request(msg):
        print(f"Received a message on '{msg.subject} {msg.reply}': {msg.data.decode()}")
        await nc.publish(msg.reply, b'I can help')

    # Use queue named 'workers' for distributing requests
    # among subscribers.
    sub = await nc.subscribe("help", "workers", help_request)

    # Send a request and expect a single response
    # and trigger timeout if not faster than 500 ms.
    try:
        response = await nc.request("help", b'help me', timeout=0.5)
        print("Received response: {message}".format(
            message=response.data.decode()))
    except TimeoutError:
        print("Request timed out")

    # Remove interest in subscription.
    await sub.unsubscribe()

    # Terminate connection to NATS.
    await nc.drain()

if __name__ == '__main__':
    asyncio.run(main())

4. Reference

https://github.com/nats-io/nats.py