无需重新启动即可升级Node.JS Web应用程序

Question

有没有办法在不重新启动的情况下更改Node.JS应用程序的代码.

例如,如果当时正在从服务器下载文件,是否有办法在不中断文件传输的情况下升级服务器？

Answer 1

是的,可以使用群集模块.

基本上,您将启动应用程序的多个从属实例,通过主进程共享同一端口.主设备将传入的连接分配给从设备.

如果要重新启动,主服务器将按顺序执行:

• 停止将连接传递给奴隶
• 轻轻地告诉它重启
• 等待它重生

这里有一些代码可以帮助您入门(您需要npm install async underscore).

注意:这只是为了让您入门.您应该准备好在真实设置中处理意外的从站故障和超时.

var cluster = require('cluster');
var http = require('http');
var _ = require('underscore');
var async = require('async');
var numCPUs = require('os').cpus().length;

if (cluster.isMaster) {
  console.log('starting master with PID', process.pid);
  // Fork workers.
  var slaves = {};

  for (var i = 0; i < numCPUs; i++) {
    cluster.fork();
  }

  cluster.on('fork', function (worker) {
    slaves[worker.id] = worker;
  });

  cluster.on('exit', function (worker, code, signal) {
    console.log('worker ' + worker.process.pid + ' died');
    delete slaves[worker.id];

    // restart the worker
    cluster.fork();
  });

  process.on('SIGHUP', function restartApp() {
    console.log('restarting all slaves');
    // important: force node.js to reload all js sources
    delete require.cache;

    var toRestart = _(slaves).values();

    async.eachSeries(toRestart, function (slave, done) {
      slave.kill('SIGTERM');

      // when the new worker starts, proceed to the next instance
      cluster.once('listening', function () {
        done();
      });
    });
  });
} else {
  console.log('- starting slave with PID', process.pid);
  // Workers can share any TCP connection
  // In this case its a HTTP server
  var server = http.createServer(function(req, res) {
    res.writeHead(200);
    res.end("hello world\n");
  });

  process.on('SIGTERM', function () {
    // finish all current connections, then stop
    server.close(function () {
      process.exit(0);
    });
  });

  server.listen(8000);
}

当你调用`kill -HUP时,你会看到它按顺序重启所有的slave:

worker 5156 died
- starting slave with PID 5164
worker 5157 died
- starting slave with PID 5165
worker 5158 died
- starting slave with PID 5166
worker 5159 died
- starting slave with PID 5167

重新启动时,总​​有3个正在运行的从站来处理传入连接.

最后一件事:如果你尝试,console.log在slave SIGTERM处理程序中没有做任何事情,因为它已经与master断开连接.