Is rotating child processes in node.js/cluster good idea?

Question

Is rotating child processes in node.js/cluster good idea?

Apache Web Server has a config parameter called MaxRequestsPerChild. http://httpd.apache.org/docs/2.0/en/mod/mpm_common.html#maxrequestsperchild "After MaxRequestsPerChild requests, the child process will die."

To avoid crush caused by memory leaks, too many connections, or other unexpected errors, should I do the same thing when using node.js Cluster module?

*I'm using Nginx in front of node.js, not Apache. I mentioned to it so that I could easily explain.

I just implemented it like this:

var maxReqsPerChild = 10; // Small number for debug
var numReqs = 0;

if (cluster.isMaster) {
  var numCPUs = require('os').cpus().length;
  for (var i = 0; i < numCPUs; i++) {
    cluster.fork();
  }

  cluster.on('death', function(worker) {
    // Fork another when one died 
    cluster.fork();
  });
} else {
  http.createServer(function(webReq, webRes) {
    // Count up
    numReqs++;

    // Doing something here

    // Kill myself
    if (numReqs > maxReqsPerChild) {
      process.kill(process.pid); // Or more simply, process.exit() is better?
    }
  }).listen(1338);
}

This has been working well up until now, but I'm wondering there is more proper way.

node.js

Answer 1

MaxRequestsPerChild is good to hide memory leak troubles, but shouldn't be used too often, because it just hides real trouble. First try to avoid the memory leaks. It shouldn't be used to avoid other issues like too many connections, nor other unexpected errors.

When you do use MaxRequetsPerChild, you shouldn't process.kill neither process.exit, because that immediately closes all undergoing connections.

Instead, you should server.close, which will wait for all undergoing connections finish, and then fires 'close' event.

var server = http.createServer(...);
server.on( "close", function() {
    process.exit(0);
});
server.on( "request", function () {
    requestCount += 1;
    if ( options.max_requests_per_child && (requestCount >= options.max_requests_per_child) ) {
        process.send({ cmd: "set", key: "overMaxRequests", value: 1 });
        if ( ! server.isClosed ) {
            server.close();
            server.isClosed = 1;
        }
    }
});

see a complete working example here: https://github.com/mash/node_angel