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98 lines
2.8 KiB
Markdown
98 lines
2.8 KiB
Markdown
# Cluster
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A single instance of Node runs in a single thread. To take advantage of
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multi-core systems the user will sometimes want to launch a cluster of Node
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processes to handle the load.
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The cluster module allows you to easily create a network of processes that
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all share server ports.
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var cluster = require('cluster');
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var http = require('http');
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var numCPUs = require('os').cpus().length;
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if (cluster.isMaster) {
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// Fork workers.
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for (var i = 0; i < numCPUs; i++) {
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cluster.fork();
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}
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cluster.on('death', function(worker) {
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console.log('worker ' + worker.pid + ' died');
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});
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} else {
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// Worker processes have a http server.
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http.Server(function(req, res) {
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res.writeHead(200);
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res.end("hello world\n");
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}).listen(8000);
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}
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Running node will now share port 8000 between the workers:
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% node server.js
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Worker 2438 online
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Worker 2437 online
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The difference between `cluster.fork()` and `child_process.fork()` is simply
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that cluster allows TCP servers to be shared between workers. `cluster.fork`
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is implemented on top of `child_process.fork`. The message passing API that
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is available with `child_process.fork` is available with `cluster` as well.
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As an example, here is a cluster which keeps count of the number of requests
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in the master process via message passing:
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var cluster = require('cluster');
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var http = require('http');
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var numReqs = 0;
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if (cluster.isMaster) {
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// Fork workers.
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for (var i = 0; i < 2; i++) {
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var worker = cluster.fork();
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worker.on('message', function(msg) {
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if (msg.cmd && msg.cmd == 'notifyRequest') {
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numReqs++;
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}
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});
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}
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setInterval(function() {
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console.log("numReqs =", numReqs);
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}, 1000);
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} else {
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// Worker processes have a http server.
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http.Server(function(req, res) {
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res.writeHead(200);
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res.end("hello world\n");
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// Send message to master process
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process.send({ cmd: 'notifyRequest' });
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}).listen(8000);
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}
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## cluster.fork()
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Spawn a new worker process. This can only be called from the master process.
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## cluster.isMaster
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## cluster.isWorker
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Boolean flags to determine if the current process is a master or a worker
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process in a cluster. A process `isMaster` if `process.env.NODE_WORKER_ID`
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is undefined.
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## Event: 'death'
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When any of the workers die the cluster module will emit the 'death' event.
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This can be used to restart the worker by calling `fork()` again.
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cluster.on('death', function(worker) {
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console.log('worker ' + worker.pid + ' died. restart...');
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cluster.fork();
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});
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Different techniques can be used to restart the worker depending on the
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application.
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