warden

A wrapper for Panopticon that makes adding measurements to your codebase simple and efficient.

Panopticon already makes it easy to sample data and aggregate it over a Node.js cluster. What warden adds is the ability to use require('warden') to gain access to one or more Panopticon instances anywhere in your project. No need to roll your own module to contain panoptica and use awkward path-like requires's to use it.

Setup

You should require warden and call it on both the cluster master and cluster workers of your service. For example:

var cluster = require('cluster');
var warden = require('warden');

// Calling setup before cluster logic is an easy way to call it on all processes.
warden.setup([/* intervals */], { /* Panopticon config */ });

// warden.setup should be run on all processes. Below is how I handle cluster.
if (cluster.isMaster && process.env.NODE_ENV === 'production') {
    require('./master.js'); // Handles all master logic.
} else {
    require('./worker.js'); // Entry point to the service logic.
}

The configuration argument is the same as that of Panopticon, but you should omit the interval field since this is overridden by the intervals argument. It turns out to be useful to have more than one instance of Panopticon with different intervals.

Usage

Once warden.setup has been called, you can simply require warden in any module you want to collect measurements in. The warden has the same measurement methods as Panopticon, and you can even add your own. See the Panopticon documentation for the logger methods. For example, an express middleware that measures response time could look like:

var warden = require('warden');

module.exports = function (req, res, next) {
    'use strict';

    var t0 = process.hrtime();

    res.once('finish', function () {
        // Δt in high resolution. Panopticon has a timedSample method that uses these.
        var t1 = process.hrtime(t0);

        // For grouping related measurements.
        var path = ['webservice', req.route.path, req.route.method];

        warden.timedSample(path, 'responseTime' t1);
    });

    next();
}

Delivery

After each interval elapses, aggregated data is emitted on the delivery event of warden. This emission only happens on master, so you must handle the data in your master process. The form of the data can be customized during setup. See here for information.