How to gracefully restart a NodeJS server?

Question

Currently, my prod environment for a side project is a git repo, where I pull in some code, manually kill the server with Ctrl-C, and restart it manually.

I realize there are a lot of things wrong with this. For instance, what if a user is still in the middle of doing something important and the process is crunching sensitive data, and I just killed it?!

When I used node v0.4.x there was a nice Cluster module that could restart the server gracefully, when the application is in a quiet state. In v0.6.x the Cluster module is built into node, but it's really, really bare, and doesn't have the graceful restart ability.

Anyone know how I can gracefully restart a nodejs server in v0.6.x?

Answer 1

You can handle POSIX signals in node code.

See in the example code, that will handle SIGINT (Ctrl-C for instance) as a STOP signal for all cluster workers, and SIGUSR2 will just restart all workers

So, issuing kill -SIGUSR2 PID, where PID is node master PID will restart all cluster

module.exports = function(app) {     var cluster = require('cluster');     var numCPUs = require('os').cpus().length;     var workerList = new Array();     var sigkill = false;      if (cluster.isMaster) {         for (var i = 0; i < numCPUs; i++) {             var env = process.env;             var worker = cluster.fork(env);             workerList.push(worker);         }          process.on('SIGUSR2',function(){             console.log("Received SIGUSR2 from system");             console.log("There are " + workerList.length + " workers running");             workerList.forEach(function(worker){                 console.log("Sending STOP message to worker PID=" + worker.pid);                 worker.send({cmd: "stop"});             });         });          process.on('SIGINT',function(){             sigkill = true;             process.exit();         });          cluster.on('death', function(worker) {             if (sigkill) {                 logger.warn("SIGKINT received - not respawning workers");                 return;             }             var newWorker = cluster.fork();             console.log('Worker ' + worker.pid + ' died and it will be re-spawned');              removeWorkerFromListByPID(worker.pid);             workerList.push(newWorker);         });     } else {         process.on('message', function(msg) {             if (msg.cmd && msg.cmd == 'stop') {                 console.log("Received STOP signal from master");                 app.close();                 process.exit();             }         });         app.listen(3000);     }      function removeWorkerFromListByPID(pid) {         var counter = -1;         workerList.forEach(function(worker){             ++counter;             if (worker.pid === pid) {                 workerList.splice(counter, 1);             }         });     } } 

Answer 2

There's a module named Forever.

That can gracefully restart the process. I suppose then you can somehow run several instances with cluster (one on each core) and use Forever to monitor / restart them.

This is just an option I found; I'm open to suggestions!