notare-monitor -- Node.js observer

Extracted from the notare module, notare-monitor provides a Node.js streams Readable that monitors and reports on various Node.js performance metrics.

Example

const { Monitor } = require('notare-monitor');
const { pipeline, Writable } = require('stream');

class myWritable extends Writable {
  constructor() {
    super({ objectMode: true });
  }
  _write(chunk, encoding, callback) {
    console.log(JSON.stringify(chunk));
    callback();
  }
}

const monitor = new Monitor();
pipeline(monitor, new myWritable(), (err) => {
  if (err) {
    console.error('There was an error!');
    process.exit(1);
  }
});

API

Constructor: Monitor([options])

Create a new 'Monitor object.

• options (object)
  • hz: (number) An integer between 1 and 1000 that specifies the number of samples per second the Monitor should generate. The higher this number, the greater the performance impact the Monitor will have. The default is 2. The NOTARE_HZ environment variable may also be used to set this value.
  • handles: (boolean) When true, the Monitor will track and report on the number of async resources in use by Node.js. Enabling this has a measurable performance impact on the Node.js process so it is off by default. Setting the NOTARE_HANDLES environment variable to 1 may also be used to set this value.
  • gc: (boolean) When true, the Monitor will track and report on garbage collection counts and durations. Enabling this has a measurable performance impact on the Node.js process so it is off by default. Setting the NOTARE_GC environment variable to 1 may also be used to set this value.

The Monitor object extends from Node.js stream.Readable.

Configuration via Environment Variables

• NOTARE_HZ=n where n is the number of samples per second (default 2)
• NOTARE_HANDLES=1 instructs notare to monitor async hook handle counts (disabled by default)
• NOTARE_GZ=1 instructs notare to monitor garbage collection (disabled by default)