cluster.fork

Learn to create workers with cluster.fork.

The cluster.fork method

The cluster.fork() method starts a new worker process and returns a Worker object. The worker runs the same code as the master; but since cluster.isMaster is false, it enters the worker branch.

A typical pattern is to start as many workers as CPUs. require("os").cpus().length gives the core count. Each worker listens on the same port; cluster distributes the load among them.

The Worker object

cluster.fork() returns a Worker object. Each worker has a unique id, the child process it runs in, and a send method.

You send messages from master to worker with worker.send(msg). The worker catches it with process.on("message"). This works over an IPC (inter-process communication) channel. The Worker object also exposes worker.process.pid for the process id, which is handy for logging and monitoring.

Exercise Log the type of fork

Import the cluster module. Log typeof cluster.fork with console.log.

Show example solution

const cluster = require("cluster");
console.log(typeof cluster.fork);

Test yourself

Write the worker-starting method
```
cluster.____()
```
Show answer
```
cluster.fork()
```
What does cluster.fork() return?
- Bir dize
- A Worker instance
- A number (PID)
- undefined
Show answer

A Worker instance — cluster.fork() returns a Worker instance.
Match each piece to its role

cluster.fork()

Starts a worker
worker.process

Child process
worker.id

Unique id
worker.send

Message to worker

Next lesson: Worker IPC

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