setupPrimary is used to change the default 'fork' behavior. Once called, the settings will be present in cluster.settings.

Any settings changes only affect future calls to .fork() and have no effect on workers that are already running.

The only attribute of a worker that cannot be set via .setupPrimary() is the env passed to .fork().

The defaults above apply to the first call only; the defaults for later calls are the current values at the time of cluster.setupPrimary() is called.

import cluster from 'node:cluster';

cluster.setupPrimary({
  exec: 'worker.js',
  args: ['--use', 'https'],
  silent: true,
});
cluster.fork(); // https worker
cluster.setupPrimary({
  exec: 'worker.js',
  args: ['--use', 'http'],
});
cluster.fork(); // http worker

This can only be called from the primary process.