NodeJS cluster global variable

Question

I'm trying to execute a function in a specific cluster, but I'm having some strange issues with assigning variables in my master process.

const cluster   = require('cluster');

let _checkId = null; // This stores the cluster id

if(cluster.isMaster) {
    for(let i = 0; i < 4; i++) {
        // Assign _checkId
        if(_checkId === null) _checkId = (i + 1);

        console.log(_checkId);

        cluster.fork();
    }
} else {
    console.log('Cluster id: ' + cluster.worker.id);
    console.log('_checkId ' + _checkId);
    console.log(_checkId === cluster.worker.id);
}

The output for this is:

1
1
1
Cluster id: 3
_checkId null // --> This doesn't make sense
false
Cluster id: 1
_checkId null
false
Cluster id: 2
_checkId null
false

Essentially what I'm trying to achieve is that I can have multiple clusters, but only one cluster should execute a specific function.

Answer 1

It's doing exactly what you're specifying to do: _checkId does equal null, and only is assigned on your master process

const cluster   = require('cluster');

let _checkId = null; // This stores the cluster id

if(cluster.isMaster) {
    for(let i = 0; i < 4; i++) {
        // Assign _checkId
        if(_checkId === null) _checkId = (i + 1);

        console.log(_checkId);

        cluster.fork();
    }
} else {
    // _checkId remains null
    _checkId = 'foo';
    console.log('Cluster id: ' + cluster.worker.id);
    console.log('_checkId ' + _checkId);
    console.log(_checkId === cluster.worker.id);
}

This yields

Cluster id: 3
_checkId foo // --> This makes sense
...
Cluster id: 1
_checkId foo
...
Cluster id: 2
_checkId foo
...