http-proxyを使ったWebSocket対応のreverse proxy。 proxy先のHostの情報のJSONファイルを監視していて、変更があれば読み込むようになっているため動的にproxy先のサーバを変更できる。死活監視プログラムがJSONを作成すればFailOverが実現できる。

dinamic_reverse_proxy.js

var http = require('http')
, httpProxy = require('http-proxy')
, Cookie = require('cookie')
, fs = require('fs');

var SERVERS_FILE_NAME = "servers.json"
var PROXY_PORT = 4000

var SERVERS = null;
var g_httpProxies = {};

function readValidServersInfo(){
  fs.readFile(SERVERS_FILE_NAME,function(err,data){
    try{
      if(err) throw err;
      currentServers = JSON.parse(data);
      if(currentServers.length == 0) throw new Error("valid server was not existed.");
      SERVERS = currentServers;
      console.log(SERVERS);
    }catch(e){
      console.log(e);
      if(SERVERS == null){
        exit();
      }
    }
  });
}

function decideHost(){
  var idx = Math.floor(Math.random() * SERVERS.length);
  return {key: idx + ":" + SERVERS[idx].host + SERVERS[idx].port,host: SERVERS[idx].host,port: SERVERS[idx].port};
}

function decideHostFromKey(key){
  var sPos = key.indexOf(":");
  if(sPos == -1){
    return decideHost();
  }
  var index = key.substr(0,sPos);
  var serverWithPort = key.substr(sPos + 1,key.length - sPos - 1);
  var serverInfo = SERVERS[index];
  if(serverInfo && (serverInfo.host + serverInfo.port) == serverWithPort){
    return {key: key,host: serverInfo.host,port: serverInfo.port};
  }else{
    SERVERS.forEach(function(server){ 
      if((server.host + server.port) == serverWithPort){
        return {key: key,host: server.host,port: server.port};
      }
    });
  }
  return decideHost();
}

function getProxyInfo(req){
  var target,cookie;
  if(req.headers.cookie){
    cookie = Cookie.parse(req.headers.cookie);
    if(cookie && cookie.proxyKey){
      return decideHostFromKey(cookie.proxyKey);
    }
  }
  return decideHost();
}

function findOrCreateHttpProxy(req,res){
  var proxyInfo = getProxyInfo(req);
  if(res){
    res.setHeader('Set-Cookie', 'proxyKey=' + proxyInfo.key);
  }
  if(! g_httpProxies[proxyInfo.key]){
    g_httpProxies[proxyInfo.key] = new httpProxy.HttpProxy({target: { host: proxyInfo.host ,port: proxyInfo.port }});
  }
  return g_httpProxies[proxyInfo.key];
}

readValidServersInfo();

fs.watchFile(SERVERS_FILE_NAME,function(curr,filename){
  readValidServersInfo();
});

var server = http.createServer(function(req,res){
  var proxy = findOrCreateHttpProxy(req,res);
  proxy.proxyRequest(req,res);
});

server.on('upgrade',function(req,socket,head){
  var proxy = findOrCreateHttpProxy(req);
  proxy.proxyWebSocketRequest(req,socket,head);
});

server.listen(PROXY_PORT);