http-master-proxy

http-master-proxy

proxy mutable HTTP traffic to an elected master

useful if you have a HTTP api where writes must be sent to an elected master but reads can be served from any node in the cluster

install

$ npm install http-master-proxy

usage

Create a locked node so we have a consensus on the leader

Then make a function which will proxy POST,PUT and DELETE requests onto the elected master

var http = require("http")
var locked = require("locked")
var masterProxy = require('http-master-proxy')
 
var serverid = process.env.NODEID
var serveraddress = '127.0.0.1:' + process.env.NODEPORT
 
// create a locker passing etcd connection details
var locker = locked('127.0.0.1:4001,127.0.0.1:4002')
 
// create a lock with a value that is the address for our HTTP server
var node = locker({
    id:serverid,
    path:'/myservice',
    value:serveraddress,
    ttl:10
})
 
var proxy = masterProxy(function(){
 
    // return if the current server is the leader
    return node.isSelected()
 
},function(){
 
    // return the address of the current leader
    return node.value()
    
})
 
var server = http.createServer(proxy(function(req, res){
    
    if(req.url=='/api/v1/leader'){
        res.end(node.id() + "\n")
        return
    }
 
    if(req.method=='GET'){
        res.end('get ' + serverid + "\n")
    }
    else{
        res.end('post ' + serverid + "\n")
    }
}))
 
node.start()
server.listen(process.env.NODEPORT)

If we ran 3 copies of the server above:

$ NODEID=node1 NODEPORT=8080 node example.js
$ NODEID=node2 NODEPORT=8081 node example.js
$ NODEID=node3 NODEPORT=8082 node example.js

We can see that the server we hit will handle the request:

$ curl -L http://127.0.0.1:8080/api/v1/blog
get node1
$ curl -L http://127.0.0.1:8081/api/v1/blog
get node2
$ curl -L http://127.0.0.1:8082/api/v1/blog
get node3

Lets see which server is currently elected as master:

$ curl -L http://127.0.0.1:8082/api/v1/leader
node2

Then we should expect node2 to handle all POST requests across the whole cluster:

$ curl -L http://127.0.0.1:8080/api/v1/blog -XPOST -d value=bar
post node2
$ curl -L http://127.0.0.1:8081/api/v1/blog -XPOST -d value=bar
post node2
$ curl -L http://127.0.0.1:8082/api/v1/blog -XPOST -d value=bar
post node2

api

var proxy = electedhttp(leaderfn, addressfn)

Create a proxy function that will proxy POST, PUT and DELETE requests

leaderfn is a function that returns a boolean as to whether this node is the current master

addressfn is a function that returns the address of the current master

var handler = proxy(function handle(req, res){})

Return a handler function that will be proxied to the master for POST,PUT and DELETE requests

var server = http.createServer(proxy(function(req, res){
    
    // if not GET request then this will be the master
    
}))

license

MIT