NATS-streaming-server.md

Stan

• stan means nats client in community name convention

Creating a stan (publisher)

import nats from 'node-nats-streaming'

const stan = nats.connect('ClusterID', 'ClientID', {
  url: 'http://XXXXX'
})

• ClusterID is defined in Deployment file with -cid flag

Queue Group

We can have Queue Groups associated to a channel to limit that only one of listener services get the desired event.

NATS Streaming Server's default channel count is 1000

Creating subscription with Queue Group (listener)

const subscription = stan.subscribe('ChannelName', 'QueueGroupName')
subscription.on('message', (msg: Message) => {
  const messageData = msg.getData()
})

• Channel Name is case sensitive!

Subscription Options

Examples:

// create Option
const options = stan.subscriptionOptions()
  .setDeliverAllAvailable()
  .setManualAckMode()
  .setMaxInFlight()
  .setDurableName() // use to memorize processed Events inside NATS server

// and pass it as 3rd argument
const subscription = stan.subscrib('ChannelName', 'QueueGroupName', options)

Example setting ManualAckMode

Default Ack Time is 30 seconds.

const options = stan.subscriptionOptions()
  .setManualAckMode(true)

const subscription = stan.subscribe('ChannelName', 'QueueGroupName')
subscription.on('message', (msg: Message) => {
  msg.ack() // acknowledge the message!
})

Message Class

• message.getSubject() returns channel name.
• message.getSequence() returns the sequence number of the message. (starting from 1)
• message.getData() returns the data associated with the message payload. If the stanEncoding is not set to 'binary', a string is returned.

Monitoring NATS streaming server

localhost:MONITORINGP-PORT/

To check specific channel,

ocalhost:MONITORINGP-PORT/streaming/channels?subs=1

Deployment example

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nats-depl
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nats
  template:
    metadata:
      labels:
        app: nats
    spec:
      containers:
        - name: nats
          image: nats-streaming:0.17.0
          args: [
              '-p',
              '4222',
              '-m',
              '8222',
              '-hbi', # heartbeat, NATS server is going to send to all of its different connected clients every so many seconds
              '5s',
              '-hbt', # how long each client has to respond
              '5s',
              '-hbf', # number of times that each client can fail before NATS streaming server is going to assume that connection is dead and gone
              '2',
              '-SD',
              '-cid',
              'ticketing',
            ]
---
apiVersion: v1
kind: Service
metadata:
  name: nats-srv
spec:
  selector:
    app: nats
  ports:
    - name: client
      protocol: TCP
      port: 4222
      targetPort: 4222
    - name: monitoring
      protocol: TCP
      port: 8222
      targetPort: 8222

TypeScript Alternatives with Croos Language Support for event types sharing

• JSON Schema
• Protobuf
• Apache Avro