Workers

A worker is a long-lived process that starts with the server and stops with it: a listener on a message broker, a connection to a device, a cache warmer. It takes no arguments, it is never retried and nothing records that it ran. Work that happens because something happened — a mail to send, an upload to process, anything with arguments that should be retried and looked at afterwards — is a job, not a worker; so is anything a worker would do on a setInterval, which a recurring job does across restarts and without running once per server process.

Files under app/workers (subdirectories included) are loaded when the application boots, in alphabetical order, and reloaded when they change. A worker exports start(henri) and stop(henri); start is awaited before the next worker starts, stop is called on reload and on shutdown. A name is used in the logs instead of the file name.

henri generate worker heartbeat   # writes app/workers/heartbeat.js
henri destroy worker heartbeat

app/workers/heartbeat.js

let timer = null;

module.exports = {
  name: 'heartbeat',

  start: async (henri) => {
    henri.pen.info('heartbeat', 'started');
    timer = setInterval(() => henri.pen.info('heartbeat', 'tick'), 60000);
  },

  stop: async (henri) => {
    clearInterval(timer);
    timer = null;
    henri.pen.info('heartbeat', 'stopped');
  },
};

A worker without a start function is loaded and reported, not started. A stop that throws is logged and does not prevent the others from stopping.

henri jobs never starts them: a job runner is not a web process. henri server --skip-workers (or SKIP_WORKERS=1) boots without them, which is handy when a worker talks to an external service you do not want to hit while developing. @usehenri/testing skips them too unless setup({ workers: true }) is called.