How port is reused by multiple node application process - node.js

Question

When I run the same application which uses os port multiple times in java application(example ) I get below exception.
Exception in thread "main" java.net.BindException: Address already in use
at sun.nio.ch.Net.bind0(Native Method)
at sun.nio.ch.Net.bind(Net.java:433)
at sun.nio.ch.Net.bind(Net.java:425)
at sun.nio.ch.ServerSocketChannelImpl.bind(ServerSocketChannelImpl.java:223)
node_cluster.js
const cluster = require('cluster'),
cpus = require('os').cpus().length;
cluster.setupMaster({
exec: '3_worker.js'
});
if(cluster.isMaster) {
for(let i = 0; i< cpus; i++) {
cluster.fork();
}
cluster.on('fork', worker => console.log(worker.id + " is forked"));
cluster.on('listening', (worker, address) => console.log(worker.id + "is listening on " + JSON.stringify(address)));
cluster.on('online', worker => console.log(`${worker.id} is online`));
cluster.on('disconnect', worker => console.log(`${worker.id} is disconnected`));
cluster.on('exit', (worker, code, signal) => console.log(`${worker.id} is dead due to ${code} and ${signal}`));
}
3_worker.js
const http = require('http');
http.createServer((req, res) => {
console.log(req.url);
res.writeHead(200);
res.end('hello');
}).listen(8080);
The above programs return result -
3is listening on {"addressType":4,"address":null,"port":8080}
5is listening on {"addressType":4,"address":null,"port":8080}
4is listening on {"addressType":4,"address":null,"port":8080}
7is listening on {"addressType":4,"address":null,"port":8080}
8is listening on {"addressType":4,"address":null,"port":8080}
2is listening on {"addressType":4,"address":null,"port":8080}
1is listening on {"addressType":4,"address":null,"port":8080}
6is listening on {"addressType":4,"address":null,"port":8080}
The output of ps is -
$ ps
PID TTY TIME CMD
4477 ttys001 0:00.16 /bin/bash -l
5219 ttys001 0:00.12 node 3_clustering.js
5220 ttys001 0:00.14 /Users/rajkumar.natarajan/.nvm/versions/node/v8.15.0/b
5221 ttys001 0:00.14 /Users/rajkumar.natarajan/.nvm/versions/node/v8.15.0/b
5222 ttys001 0:00.13 /Users/rajkumar.natarajan/.nvm/versions/node/v8.15.0/b
5223 ttys001 0:00.14 /Users/rajkumar.natarajan/.nvm/versions/node/v8.15.0/b
5224 ttys001 0:00.14 /Users/rajkumar.natarajan/.nvm/versions/node/v8.15.0/b
5225 ttys001 0:00.14 /Users/rajkumar.natarajan/.nvm/versions/node/v8.15.0/b
5226 ttys001 0:00.14 /Users/rajkumar.natarajan/.nvm/versions/node/v8.15.0/b
5227 ttys001 0:00.14 /Users/rajkumar.natarajan/.nvm/versions/node/v8.15.0/b
5794 ttys002 0:00.05 /bin/bash --rcfile /Applications/IntelliJ IDEA.app/Con
6063 ttys003 0:00.03 /Applications/Utilities/iTerm.app/Contents/MacOS/iTerm
6065 ttys003 0:00.04 -bash
How multiple node.js process are able to listen on same port.

Answer 1

Only the master has the port opened. It handles all incoming and outgoing traffic on the port and offloads the traffic to the worker threads for processing.