express-swim

An http-based SWIM gossip protocol implementation, for expressjs apps

http://www.cs.cornell.edu/~asdas/research/dsn02-swim.pdf http://www.cs.ucsb.edu/~ravenben/classes/papers/aodv-wmcsa99.pdf

Getting started

Install via npm

$ npm install optimist express express-swim

Create your app.js

var argv= require('optimist').argv,
    express= require('express'),
    swim= require('express-swim');

var app= express(), node= [argv.host,argv.port].join(':');

app.use('/swim',swim(node,{ verbose: true }));

app.listen(argv.port,argv.host);
console.log(node+' listening...');

In different terminals launch a bunch of nodes:

$ node app.js --host 127.0.0.1 --port 8001

$ node app.js --host 127.0.0.1 --port 8002

$ node app.js --host 127.0.0.1 --port 8003

and let them join the cluster:

$ curl -X POST -d '127.0.0.1:8001' http://127.0.0.1:8002/swim/join
$ curl -X POST -d '127.0.0.1:8001' http://127.0.0.1:8003/swim/join

Ok, now you have a connected cluster... Lets break it! Try to CTRL-C some node, and see what the other nodes are doing. At any time you can ask for the list of active nodes to any node

$ curl http://127.0.0.1:8001/swim/nodes

You can subscribe membership updates like this:

var argv= require('optimist').argv,
    express= require('express'),
    swim= require('express-swim');

var app= express(), node= [argv.host,argv.port].join(':');

var swimApp= swim(node,{ verbose: true });

app.use('/swim',swimApp);

app.listen(argv.port,argv.host);
console.log(node+' listening...');

swimApp.swim.on('join',function (server)
{
    console.log(server,'joined');
});

swimApp.swim.on('leave',function (server)
{
    console.log(server,'leaved');
});

swimApp.swim.on('fail',function (server)
{
    console.log(server,'failed');
});

NOTE: you could receive those message more than one time (per event).

piggybacking

SWIM uses piggybacking of failure detection messages to disseminate group membership info accross the cluster. And you can use the same strategy to propagate your app messages:

var argv= require('optimist').argv,
    express= require('express'),
    swim= require('express-swim');

var app= express(), node= [argv.host,argv.port].join(':');

var swimApp= swim(node,{ verbose: true });

app.use('/swim',swimApp);

app.listen(argv.port,argv.host);
console.log(node+' listening...');

swimApp.swim.on('hello',function (world)
{
    console.log(world);
});

setInterval(function ()
{
    swimApp.swim.send('hello',{ world: node });
},5000);