Event Streamer

Description

Event Streamer is a library for connect micro services based on kafka event communication.

This is a wrap of kafka-js simplifying connection, errors and topic with subject (event name, event code).

This library is not intended to consume two different clusters at the same time, but you can produce in two or more clusters at the same time.

Installation

yarn:

$ yarn add @comparaonline/event-streamer

Initialization

Before use it, it should be initialized calling the method setConfig

Basic producer configuration

With this it will be enough to produce any message

import { setConfig } from '@comparaonline/events-streamer'

setConfig({
  host: 'kafka:9092'
})

Basic consumer configuration

The only difference if you also need to consume events is that consumer group id is required

import { setConfig } from '@comparaonline/events-streamer'

setConfig({
  host: 'kafka:9092',
  consumer: {
    groupId: 'my-group-id'
  }
})

Full configuration

Usage

Event subject

Event subject, event code or event name is intended to allow send multiple messages into the same topic but handling them in different ways.

Produced messages will be delivered as JSON string with an extra property called 'code'. This code will be the event subject. Subject will be always passed to UpperCamelCase replacing -_ and transforming the first character after each of them into upper case. Eg:

• my-event-name
• my event name
• my_event_name
• myEventName

All this will be transformed to MyEventName

If a subject is not provided then the topic will be transformed to UpperCamelCase and sended as subject.

Consumed messages with invalid JSON will be ignored. If the messages is a valid JSON but without code property it will be only handled by global listeners.

Producing

Event streamer will create and close kafka client on demand to avoid keeping open connections, this connection will be reused until TTL is reached (TTL is renewed after each execution). Produced events will be delivered the data object into a single topic as JSON string with the corresponding subject. It will also add appName and createdAt properties

App name

appName is a first-level property with sender name. event-streamer has this options to set appName

1. Sending appName property on messages
2. Perform event-streamer initialization with appName property
3. Read consumerGroupId from event-streamer initialization and use it as appName
4. Read process.env.HOSTNAME. This is automatically setup on K8S deployment
5. Set unknown string

Message date

every message should have a property createdAt, it is message creation date on ISO UTC format. event-streamer add this property automatically

Single event

import { emit } from '@comparaonline/event-streamer'

// Remember to call setConfig before use this method

async function main () {
  await emit({
    topic: 'my-topic',
    eventName: 'my-event-name',
    data: { firstName: 'John' }
  })
  
  // Topic: my-topic Message: { "firstName": "John", "code": "MyEventName", "createdAt": "2024-03-07 18:41:54Z", "appName": "test" }

}

Single event with alternative syntax

import { emit } from '@comparaonline/event-streamer'

async function main () {
  await emit('my-topic', 'my-event-name', { firstName: 'John' })
  // Topic: my-topic Message: { "firstName": "John", "code": "MyEventName", "createdAt": "2024-03-07 18:41:54Z", "appName": "test" }

  await emit('my-topic', { firstName: 'John' })
  // Topic: my-topic Message: { "firstName": "John", "code": "MyTopic", "createdAt": "2024-03-07 18:41:54Z", "appName": "test" }
}

Two events to the same topic

import { emit } from '@comparaonline/event-streamer'

async function main () {
  await emit({
    topic: 'my-topic',
    eventName: 'my-event-name',
    data: [{ firstName: 'John' }, { firstName: 'Jane' }]
  })
  
  // Topic: my-topic Message: { "firstName": "John", "code": "MyEventName", "createdAt": "2024-03-07 18:41:54Z", "appName": "test" }
  // Topic: my-topic Message: { "firstName": "Jane", "code": "MyEventName", "createdAt": "2024-03-07 18:41:54Z", "appName": "test" }

}

Two events to two different topics

import { emit } from '@comparaonline/event-streamer'

async function main () {
  await emit(
    [
      {
        topic: 'my-topic-a',
        eventName: 'my-event-name',
        data: { firstName: 'John' }
      },
      {
        topic: 'my-topic-b',
        eventName: 'my-event-name',
        data: { firstName: 'Jane' }
      }
    ]
  )
  
  // Topic: my-topic-a Message: { "firstName": "John", "code": "MyEventName", "createdAt": "2024-03-07 18:41:54Z", "appName": "test" }
  // Topic: my-topic-b Message: { "firstName": "Jane", "code": "MyEventName", "createdAt": "2024-03-07 18:41:54Z", "appName": "test" }
}

Single event without subject

import { emit } from '@comparaonline/event-streamer'

async function main () {
  await emit({
    topic: 'my-topic',
    data: { firstName: 'John' }
  })
  
  // Topic: my-topic Message: { "firstName": "John", "code": "MyTopic", "createdAt": "2024-03-07 18:41:54Z", "appName": "test" }
}

Single event to a different host/cluster

import { emit, setConfig } from '@comparaonline/event-streamer'

setConfig({
  host: 'kafka-gpc:9092',
  producer: {
    additionalHosts: ['kafka-aws:9092']
  }
})

async function main () {
  await emit({
    topic: 'my-topic',
    data: { firstName: 'John' }
  }, 'kafka-azure:9092')
  
  // Cluster: kafka-azure:9092
  // Topic: my-topic Message: { "firstName": "John", "code": "MyTopic" }
}

Not allowed by subject

import { emit } from '@comparaonline/event-streamer'

async function main () {
  await emit({
    topic: 'my-topic',
    data: { firstName: 'John', code: 'Code' }
  }) // Throw Error: 'Reserved object keyword "code" inside data'
}

import { emit } from '@comparaonline/event-streamer'

async function main () {
  await emit({
    topic: 'my-topic',
    data: { firstName: 'John' },
    eventName: ''
  }) // Throw Error: 'Invalid message code'
}

Consuming

You will need at least 1 topic to listen. It's important to know size of messages that will be fetched because this will determine how many messages will be processed at the same time. Eg:

Data object delivered to the handler (first parameter) will be an object that includes code property

Emit function delivered to the handler (second parameter) is the same emit function used to produce events, but you won't need to import it

import { ConsumerRouter } from '@comparaonline/event-streamer'

// Remember to call setConfig with a groupId

async function main () {
  const consumer = new ConsumerRouter()

  // This handler will be executed with every message from 'topic-a', even if they don't have 'code' property
  consumer.add('topic-a', (data, emit) => { console.log(1) })

  // This handler will be executed only with messages from 'topic-b' with property 'code' equal to 'EventNameB'
  consumer.add('topic-b', 'event-name-b', (data, emit) => { console.log(2) })

  // This handler will be executed with message from 'topic-c' with property 'code' equal to 'EventNameC1' or 'EventNameC2'
  consumer.add('topic-c', ['event-name-c-1', 'event-name-c-2'], (data, emit) => { console.log(3) }) 

  // This handler will be executed with every message from 'topic-d' or 'topic-e'
  consumer.add(['topic-d', 'topic-e'], (data, emit) => { console.log(4) })

  // This handler will be executed with messages from 'topic-e' or 'topic-f' with property 'code' equal to 'MyEventName'
  consumer.add(['topic-e', 'topic-f'], 'my-event-name', (data, emit) => { console.log(5) })

  // This handler will be executed with messages from 'topic-g' and 'topic-h' with property 'code' equal to 'MyEventName1' or 'MyEventName2'
  consumer.add(['topic-g', 'topic-h'], ['my-event-name-1', 'my-event-name-2'], (data, emit) => { console.log(6) })

  // Alternative syntax 

  consumer.add({
    topic: 'topic-i',
    eventName: 'my-event-name-i', // this is optional
    callback: (data, emit) => { console.log(6) }
  })
  
  await consumer.start()
}

Input / Output example

Testing

When you need to perform unit/integration tests but you are not intended to connect with a real kafka server then, you can simply use it offline.

To do this call setConfig with onlyTesting on true on your jest setup. This will be enable you to use extra methods

Setup

// src/test/setup/event-streamer.ts
import { setConfig } from '@comparaonline/event-streamer'

setConfig({
  host: 'any-host',
  consumer: {
    groupId: 'fake-group-id'
  },
  onlyTesting: true
})

Event server

// src/event-server/index.ts
import { ConsumerRouter } from '@comparaonline/event-streamer'
import { application } from '../application'

// Remember to call setConfig with a groupId

export const consumer = new ConsumerRouter()
consumer.add('topic-a', 'event-name-a', async (data, emit) => { 
  await emit({
    topic: 'topic-b',
    data: {
      message: 'Event received'
    }
  })
})

application.onStart(async () => {
  await consumer.start()
})

Service

// src/services/my-service/__tests__/index.test.ts
import { consumer } from '../../../event-server'
import { getEmittedEvents, clearEmittedEvents, getParsedEmittedEvents } from '@comparaonline/event-server'

describe('Testing some handlers', () => {
  beforeEach(() => {
    clearEmittedEvents()
  });

  describe('Testing EventNameA', () => {
    it('Should emit event into topic b', async () => {
      await consumer.input({
        data: { someData: true },
        topic: 'a',
        eventName: 'event-name-a'
      })

      const events = getEmittedEvents()

      expect(events[0]).toMatchObject({
        topic: 'topic-b',
        messages: [
          JSON.stringify({
            message: 'Event received',
            code: 'TopicB'
          })
        ]
      })
    })

    it('Should emit event into topic c with parsed event', async () => {
      await consumer.input({
        data: { someData: true },
        topic: 'a',
        eventName: 'event-name-a'
      })

      const events = getEmittedEvents()

      expect(events[0]).toMatchObject({
        topic: 'topic-b',
        eventName: 'TopicB',
        data: {
          message: 'Event received',
          code: 'TopicB'
        }
      })
    })
  })
})

Migration to version +8.0.0

Node version

You need node version greater than or equal to v14.17.0. A good choice for Dockerfile is node:14.17.0-alpine3.13 at least than you already want to go with node:16.13-alpine3.15

Known issues after update node

• pg: if you are using a previous version from node v13 with pg v7.X.X then it will not run anymore. The easiest way to fix it is with yarn add pg@8.0.3
• python: in your docker file change python to python3

Topics and subjects

Listeners

Previous versions read all the topics and performs actions from every event not mattering the topic. Now you need to link topic/event/handler

// Option A: you know where the event came from
consumer.add('topic-a', 'my-event-name', myHandler)

// Option B: you don't know where the event came from
consumer.add(['topic-a', 'topic-b'], 'my-event-name', myHandler)

// Option C: you know where the event came from but there are two input events with the same action
consumer.add('topic-a', ['my-event-name-a', 'my-event-name-b'], myHandler)

// Option D: you don't know where the event came from but there are two input events with the same action
consumer.add(['topic-a', 'topic-b'], ['my-event-name-a', 'my-event-name-b'], myHandler)

Events subjects

Previous event-streamer version uses class name as event subject. Now you need to specify them, no matter what the event subject will be automatically converted to upper camel case

Tips

• You can transform your events folder into simple TS interfaces
• Create a kafka service folder with all the emits events

Migration PRs

Flux comparador sync

Results connector

Quoteapp CICL