xyz.send.round.robin

Round Robin Send Strategy for xyz Edit

This repository demonstrates how a send strategy can be used to implement an internal load balancing. Keep in mind that client messages will usually go through an external load balancer, then a front microservice that translates a possible client requests into an internal message. This is another story for another day. At this point we want to handle this simple issue:

A given node, say our faviorite string.ms has been scaled from one instance into three instances. How can we distribute the load so that we actually reap a benefit from this scaling?

The answer is this module.

Description

xyz.send.round.robin will keep track of all nodes that it has already sent messages to. when it receives a message that can be sent to three nodes based on path, it sends the message to one of them (the module is basically an extension to firstFind) in a sequential manner.

note that this module is a node-based balancer and does not resolve paths. Hence, any wildcard is not allowed.

To further clarify this, in the following topology, if all string.ms nodes share the same functions including /string/up and math.ms tries to send 3 messages to /string/up, each string.ms will receive one message.

This can be further justified in xyz-cli. If you run the test cases using $ xyz dev -c ./xyztestrc.json, the example explained above will be launched. As you see, the outgoing traffic of math.ms, ~90 msg/sec, is distributed fairly among three nodes, each receiving ~30 msg/sec.

Usage

The module can be installed using:

$ np install xyz.send.round.robin

It can be used both as the defaultSendStrategy:

const RR = require('xyz.send.round.robin')
var ms = new XYZ({
  selfConf: {
    logLevel: 'verbose',
    name: 'math.ms',
    host: '127.0.0.1',
    defaultSendStrategy: RR
  },
  systemConf: {nodes: []}
})

or per call

ms.call({
  servicePath: 'string/up',
  payload: 'yo',
  sendStrategy: RR,
  payload: 'hello'}, (err, body, response) => {
    //
})

The test folder further explain this.