vitalsigns

Powerful and customizable application health monitoring

npm install vitalsigns
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VitalSigns

Powerful and customizable application health monitoring

Sponsored by Leadnomics.

Installation

In your project folder, type:

npm install vitalsigns

Basic Usage

Load up VitalSigns and include a few of the built-in monitors:

var VitalSigns = require('vitalsigns'),
    vitals = new VitalSigns();

vitals.monitor('cpu');
vitals.monitor('mem', {units: 'MB'});
vitals.monitor('tick');

We know the CPU hitting 100% is bad news. So is the tick.maxMs clearing 500.

vitals.unhealthyWhen('cpu', 'usage').equals(100);
vitals.unhealthyWhen('tick', 'maxMs').greaterThan(500);

Let's get application-specific. We'll monitor connections to a game and go unhealthy when they cross 200.

vitals.monitor({
    connections: function() { return Game.getConnections(); }
}, {name: 'game'});

vitals.unhealthyWhen('game', 'connections').greaterThan(200);

We need to know when we go unhealthy...

vitals.on('healthChange', function(healthy, failedChecks) {
    console.log("Server is " + (healthy ? 'healthy' : 'unhealthy') +
        ".  Failed checks:", failedChecks);
});

And we have a load balancer hitting /health and looking for a non-200 response from express.

app.get('/health', vitals.express);

The API

Constructor

VitalSigns must be instantiated to use, and can optionally receive a set of options:

var vitals = new VitalSigns({
    autoCheck: 5000,
    httpHealthy: 200,
    httpUnhealthy: 503
});

autoCheck

Default: false. The number of milliseconds to wait between automatic health checks, or boolean false to disable. Alternatively, 'true' can be specified to auto-check every 5 seconds.

httpHealthy

Default: 200. The HTTP response code to send back in the VitalSigns.express HTTP endpoint when the server is healthy.

httpUnhealthy

Default: 503. The HTTP response code to send back in the VitalSigns.express HTTP endpoint when the server is unhealthy.

Monitors

Without stats to monitor, VitalSigns does nothing! In order for it to be useful, VitalSigns must be told what monitors to use. These can be the name of a built in monitor (cpu, mem, tick, and uptime), the name of a library in your project's node_modules folder, an object, or a function. See the "Kinds of Monitors" section below for more details.

Monitors are registered with:

instance.monitor({string|object|function} monitor, [{object} options])

Options are optional. If specified, they should be a Javascript object of key/value pairs specific to the monitor being loaded. In addition, a name field can be specified to override the default name for the module. For example, the following will cause CPU reports to be grouped under 'foo' instead of 'cpu':

instance.monitor('cpu', {name: 'foo'});

Health constraints

Before or after monitors are loaded, VitalSigns can be told what values are considered unhealthy. The syntax starts with:

instance.unhealthyWhen(<monitor>, <field>)

and the following can be added to the end to complete the definition:

.equals(<value>)
.greaterThan(<value>)
.lessThan(<value>)
.not // chainable with one of the above

For example, to mark the instance as unhealthy if monitor "foo" has a field named "bar" that's equal to or less than 5, use:

instance.unhealthyWhen('foo', 'bar').not.greaterThan(5);

Many constraints can be defined on one instance of VitalSigns.

Function calls

Besides the above, the following calls are available on VitalSigns instances:

destroy()

Destructs the instance, terminating autoChecks and any intervals set by any of the attached monitors. Also removes all event listeners. This is handy to do before shutdown to eliminate any ongoing process that might prevent the process from exiting.

express

A function to be passed to Express as the endpoint for a route. This function will return HTTP 200 or 503 by default to represent healthy and unhealthy, respectively. It will also provide the full health report returned by getReport() as a JSON string with Content-type: application/json. Example:

app.get('/ping', instance.express);

{array} getFailed()

Returns an array of strings describing the constraints that failed the last time isHealthy() was called. Array will be empty if the instance was healthy as of the last check.

{object} getReport()

Returns a Javascript object with the health report: each monitor name as keys, with the value being another Javascript object mapping each monitor's fields to their values. This function also attaches a 'healthy' field at the root level with a boolean true or false representing whether the instance is healthy based on this report.

{boolean} isHealthy()

Returns true or false based on whether the instance is healthy. Also fires up to two events; see "Events" section below.

Events

VitalSigns fires up to two events when the health is checked:

healthCheck (healthy, report, failures)

Fires every time isHealthy() is called, which includes autoChecks and calls to getReport().

  • healthy boolean: true if healthy; false if not
  • report object: The raw monitor reports in a Javascript object, grouped by monitor name
  • fails array: An array of strings describing the individual constraints that failed and caused the unhealthy status. Array has length=0 if healthy.

healthChange (healthy, report, failures)

Fires when a health check is performed that causes the instance to switch from healthy to unhealthy, or vice versa. Provides the same arguments as the healthCheck event.

Kinds of Monitors

VitalSigns-compatible monitors come in all shapes and sizes. For distributed monitors, an object with 'name' and 'report' fields is highly recommended. Here are a few of the configurations:

Object with static fields

module.exports = {
    appName: "My Awesome App",
    hostname: os.hostname()
};

Object with dynamic fields

module.exports = {
    connections: function() {
        return myApp.getConnections();
    }
};

Named monitor with report function

module.exports = {
    name: 'MyMonitor',
    report: function() {
        return {
            connections: myApp.getConnections();
            lastConnection: myApp.getLastConnectionTime();
        };
    }
};

Function returning one of the above objects

module.exports = function(options) {
    if (!options)
        options = {};
    return {
        name: 'MyMonitor',
        report: function() {
            return {
                connections: myApp.getConnections();
                lastConnection: myApp.getLastConnectionTime(options.dateFormat);
            };
        }
    };
}

Built-in monitors

VitalSigns comes with a small number of application-unspecific monitors to report on general server and process health. They are:

cpu

Monitors CPU usage and load. Provides fields:

  • usage: Percent of CPU being used at this moment
  • loadAvg1: The 1-minute load average
  • loadAvg5: The 5-minute load average
  • loadAvg15: The 15-minute load average

Options:

  • sampleTime default 1000: The milliseconds over which to sample CPU usage
  • updateTime default 5000: The milliseconds to wait between samples

mem

Monitors memory usage. Provides fields:

  • free: Amount of memory currently available
  • process: Amount of memory currently being used by this node process.

Options:

  • units default B: The units in which to display RAM sizes. Legal options are B, KB, MB, GB, TB, and PB. If you can measure your RAM in PB, I accept RAM donations.

tick

Monitors the speed of the event loop. For a Node.js app, this is the single most important set of statistics available. Provides fields:

  • avgMs: Average number of milliseconds required to loop through the specified number of ticks
  • maxMs: For the last batch of samples, the milliseconds required to loop through the slowest batch of ticks
  • perSec: An estimate of how many individual ticks are being completed per second.

Options:

  • window default 10000: The number of milliseconds for which to collect batches of tick measurements before they are averaged.
  • batch default 1000: The number of ticks to be timed in a single batch. Batches of this size are what get processed to create avgMs and maxMs.
  • freq default 50: The number of milliseconds to pause between collecting batches of ticks.

uptime

Monitors application uptime. Provides fields:

  • sys: The number of seconds for which the server has been online
  • proc: The number of seconds for which this node process has been running

License

VitalSigns is distributed under the MIT license.

Credits

VitalSigns was created by Tom Frost at Leadnomics in 2013.

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