zmqbus

Peer to peer messaging bus, zero setup with failover and pub/sub functionality.

zmqbus is a distributed messaging bus and event emitter built with ZeroMQ. And it's open source.

zmqbus doesn't use a centralized broker, but instead builds a peer-to-peer network of nodes. Failover is built-in, so if a node fails the network will recover and continue sending/receving messages.

Speedy. Since zmqbus uses ZeroMQ, it is much faster than equivalent broker-based setups. However, the downside is there is no built-in message persistence nor receive reciepts.

No configuration needed, works out of the box, easy to deploy. By default all nodes in a subnet will discover each other and elect a master node. When the master node goes down, an election will be called for to elect a new master.

Usage

var zmqbus = require('zmqbus');

// Run multiple instances of this across processes/machines.
// All instances will receive/send to each other by channel.

var node = zmqbus.createNode({});
node.on('ready', function() {
	// subscribe to equity channel
	node.subscribe("equity");

	// publish a quote cluster-wide
	node.publish("equity", "AAPL", 500.0);
});

node.on('message', function(msg) {
	console.log("received " + msg);
});

API

To create a new node:

var node = require('zmqbus').createNode({});

Listen for 'ready' event before calling other methods

node.on('ready', function() {
	// node is ready
});

Listen for 'message' event for messages. msg is an array, the first element will contain the channel name.

node.on('message', function(msg) {
	// msg[0] is channel name, msg.slice(1) will contain the rest of the message
});

To listen on a specific channel, use the subcribe() method. The node will only receive messages from channels it has subscribed to. Use the special name '*' to listen to all channels.

// subscribe to equity channel
node.subscribe('equity');

There is a corresponding unsubscribe() method to stop listening from that channel.

// unsubscribe from equity channel
node.unsubscribe('equity');

To publish a message to a channel, use publish().

// publish a message to the channel
node.publish('equity', 'AAPL', 500.0);

A node can be stopped by calling stop(). Note: this may trigger an election if this node is the master node.

// stop a node. node may not be restarted nor used.
node.stop();

Examples

See example/simple.js

Use the message bus to build applications like:

• chat rooms
• lightweight cluster-wide notifications
• multiplayer game rooms

Similar services:

• Google Cloud Messaging
• PubNub
• Pusher

Advanced

require('zmqbus').createNode() accepts a config object with the following options:

• election_priority
  • A node can be assigned a higher priority, so that it gets elected ahead of lesser priority nodes.
  • Default: 0, set between 0 - 99.
• election_timeout
  • Elections receive votes from all nodes in a cluster, the election waits for up to election_timeout milliseconds before it closes.
  • Default: 2000. Set to higher value if network is lossy.
• heartbeat_period
  • Master node heartbeats with nodes using this period (in msec).
  • Default: 2000. Set to higher value if network is lossy.
• heartbeat_timeout
  • If nodes detect no heartbeat beyond this timeout (in msec), an election is called for.
  • Default: 6000. Set to higher value if network is lossy.
• multicast_addr
  • Nodes discover and elect each other through multicast UDP using this address. Nodes in a cluster are identified by multicast_addr:multicast_port. To run multiple clusters in a single physical subnet change multicast_addr:multicast_port.
  • Default: '239.1.2.4'. Set to any private multicast address, or set to '255.255.255.255' for subnet broadcast if the subnet router has issues with multicasting.
• multicast_port
  • See above.
  • Default: 45555. Set to another port number (max. 65535) to run multiple clusters on a physical subnet.

Example:

var options = { election_priority: 2, multicast_addr: '239.9.9.9', multicast_addr: '42424' };
var node = require('zmqbus').createNode(options);

Resources

• ZeroMQ

Installing

npm install

Tests

coffee test/tests