cluster-messages

A helpful Node module to make it easy to send messages between the master and workers with callbacks.

Events can be emitted by any process and received by any process.

TODO:

1. Investigate more efficient serialisation/transmission
2. Implement logger class
3. Implement emitOnce (where callback is garbage collected after all workers respond)
4. Update README
5. Add tests
6. Implement await/async
7. Add linter
8. Convert to TypeScript
9. Transpile with Babel
10. Deep merge default options
11. Support modular architecture to move messages off IPC wire

• Support HTTP, web sockets, shared memory?

12. Introduce load testing benchmarks

Usage

Require the package:

let ClusterMessages = require('cluster-messages');
let messages = new ClusterMessages();

Setting up event listeners:

messages.on('multiplication', (data, sendResponse) => {
  sendResponse(data.x * data.y);
});

Emitting events:

let data = {
  x: Math.round(Math.random() * 100),
  y: Math.round(Math.random() * 100),
};

messages.send('multiplication', data, response => {
  console.log(`${data.x} * ${data.y} = ${response}`)
})

---

.send(eventName, data, callback)

• eventName (string) - the name of the event being emitted
• data (object) - the object passed to the event listener
• callback (function) - callback invoked by the event listener, single parameter containing the response

messages.send('print', { name: 'John' }, (response) => {
  console.log(response); // 'Hi John'
});

This function will emit an event, the callback is a single parameter that is passed, this means inside the event listener only one parameter can be passed to sendResponse so it needs to be an object containing all the data.

When sent from the master:

• the event will get sent to all workers
• each time the worker calls sendResponse (the callback inside the event listener), the callback will be invoked
• e.g. if there are 3 workers, and all of them call sendResponse, the callback will be invoked 3 times

When sent from the worker:

• the event is sent to the master only

.on(eventName, callback)

• eventName (string) - the name of the event to listen for
• data (object) - single object sent by the event emitter (.send)
• callback (function) - takes two parameters, data and sendResponse (function). data is the data sent by the event emitter, sendResponse is a function that you invoke and pass the data you want to send back to the callback on the event emitter

messages.on('print', (data, sendResponse) => {
  sendResponse('Hi ' + data.name);
});

This is the event listener, the callback takes two parameters (data and sendResponse). sendResponse only takes one parameter and is sent back to wherever the event originated.

---

When initiating ClusterMessages you can pass it some options:

const ClusterMessages = require('cluster-messages');

const instanceName = 'healthMonitor';
const options = {
  metadataKey: '__metadata__',
  log: {
    level: 'warn',
    type: 'hash'
  }
};

const messages = new ClusterMessages(instanceName, options);

metadataKey

Messages are sent around as usual and can be received through cluster.on('message') or process.on('message') as expected, so the module adds a property containing metadata that is passed around with each event. As this metadata property is essentially exposed in every single message event emission within cluster or process, the metadataKey option allows you to define the name of the meta data property to ensure it does not conflict with your application.