Availability Monitor

An availability monitoring module to see the current status of web services. Currently, the only protocols supported are TCP and HTTP/HTTPS.

The initial codebase was forked from qawemlilo's ping-monitor. From here, the codebase was rewritten to suit my own personal projects. They both exist to do the same thing but work differently under the hood.

Some of these changes include:

• Rewrote the codebase to Typescript.
• Follows the Object-oriented programming (OOP) paradigm.
• Uses got instead of the native Node http and https modules. The benefits include:
  • Handles all the weirdness the HTTP/HTTPS protocol can produce.
  • Supports Async / Await, avoiding callback-hell!
  • Built-in timing - Times various phases of the HTTP request process, so we don't have to.
  • Customizable - Users of this library can specify all the little details when handling requests. E.g. Should we SSL verify or not? Should we follow redirects or not? etc. For more information on the options available, go to got.
• Added ability to use puppeteer for monitoring on complex web-services such as Single Page Applications (SPA), web-services that rely on client-side JavaScript execution, etc.

Installation

npm install availability-monitor

Quick Usage

ES6 (ECMAScript 2015) or newer / Typescript

import { Monitor } from "availability-monitor"

const bbcNewsMonitor = new Monitor({
    protocol: 'web',
    protocolOptions: {
        url: 'https://bbc.com/news',
        engine: 'got',
        httpOptions: {
            timeout: 30000 // 30 Seconds
        }
    },
    interval: 60000
})

bbcNewsMonitor.on('up', function(monitor, response) {
    // Do something with the response
    console.log(`BBC News is up. Response Time: ${response.duration}ms`)
})
bbcNewsMonitor.on('error', function(monitor, response) {
    // Do something on error
    console.log(`Could not connect to BBC News. Error: ${response}`)
})

Testing

npm test

Advanced Usage

Constructor Options

The constructor accepts an object Object, used to specify the Monitor settings when creating a Monitor instance. Below describes the fields that can be accepted.

id

Type: number | string

Description:

An identifier for this Monitor instance. Usually this identifier is a reference from sort of database, but it can be anything you want.

Example:

// Using Numbers
1
// Using String (UUID in our case)
'954f330d-9376-43d4-830f-3b4d1f615ef'

protocol

Type: SupportedProtocol

SupportedProtocol is typed to accept one of the following:

• web
• tcp

Description:

Specifies the protocol used when checking the availability of a web-service.

protocolOptions

Type: SupportedProtocolOptions

SupportedProtocolOptions is typed to accept one of the following:

• WebProtocolOptions
• TcpProtocolOptions

WebProtocolOptions is typed as an object and acccepts the following:

• url

  Type: string

  Description:

  The URL we would like to poll.

• engine

  Type: 'got' | 'puppeteer'

  Description:

  The library to use when checking the availablity. Different libraries are used for different situations.

  Use got for quick and easy availability monitoring on basic web services. This option is suitable for server-side-rendered/static websites, APIs, and any service that is not reliant on the execution of client-side JavaScript.

  Use puppeteer when the above doesn't work. Puppeteer provides control of a Chromium Browser over the DevTools Protocol. Essentially, you are checking availability via a fully-functional browser. This is helpful for SPA websites, dynamic content, producing a HAR Trace (which is done automatically).

  Technically, you could use puppeteer for all web-based monitoring, but it is inefficient to do so as you are loading a full-featured browser. This could impact performance negatively. and may increase your system requirements rapidly depending on how many web services you plan to monitor, you may need to increase your memory capacity.

  Note: You do not have to install a Chromium browser yourself to use puppeteer. A supported version will be installed when running npm install.

• httpOptions

  Type: Options

  Description:

  Visit got's options and NodeJS's https.request options which will show you all the possible fields that are accepted.

  Note, if your engine of choice is puppeteer, the only option that can be used is timeout. timeout must be number | undefined. Using Delays will be ignored, and timeout will be set to the default instead (30000 ms ~ 30 seconds).

• expect

  Type: object | undefined

  Description:

  Sometimes, connecting sucessfully is not enough. We require details to be expected in the response. This is where we specify such things.

  Items:

  • statusCode

    Type: number | undefined

    Description:

    Specify a specific status code that we expect to be seen in the response.

  • contentSearch Type: string | undefined

    Description:

    Specify a specific substring that we expect to be seen in the response body.

TcpProtocolOptions is typed as an object and acccepts the following:

• host

  Type: string

  Description:

  The host you are connecting to.

• port

  Type: number

  Description:

  The port you are connecting to on the host.

• options

  Type: Record<string, any> | undefined

  Description:

  Placeholder. This is not used for anything yet.

• expect

  Type: Record<string, any> | undefined

  Description:

  Placeholder. This is not used for anything yet.

interval

Type: number

Default: 30000 representing 30 seconds.

Description:

Number of microseconds to wait before polling the web service again.

Emitted Events

This module inherits EventEmitter. This means this module can be easily intergrated in other applications by listening to the events below:

• up - Web service is running successfully.
• down - Web service failed when expecting certain elements to be present in the response OR failed completely.
• error - Fired when there's an error caught.
• timeout - Fired when the request times out.
• start - Fired when the monitor has started.
• stop - Fired when the monitor has stopped.
• restart - Fired when the monitor is restarting.
• ping - Fired after the monitor has pinged the web-service. Occurs regardless if the web-service is up or down, produced an error or timed out.

For start, stop, restart, and ping events, only one argument is presented to event listeners, this being the Monitor instance itself.

For error, timeout, up, and down events, two arguments are presented to event listeners, this being the Monitor instance itself, and a MonitorResponse object.

MonitorResponse object

isUp

Type: boolean

Description:

A high-level approach to clarify if a web service is running or not.

responseTime

Type: number

Default: 0

Description:

The time taken from the start of the request to the end. If a value can not be determine due to some error in the request process, this will be set to 0.

error

Type: Error | undefined

Description:

Set when timeout and error are triggered. Represents the error that was caught.

data

Type: any | undefined

Description:

Generally, the response of a web service (such as a got.Response for Web Handlers), although does not have to be. Guranteed to exist when up and down are emitted.

traceroute

Type: any | undefined

Description:

When the engine used is puppeteer, this variable holds a HTTP Archive format (HAR) that can be used to analyse the browser's network activity. To grahpically view a HAR, use (Google's HAR Analyzer)[https://toolbox.googleapps.com/apps/har_analyzer/].

monitor.isTicking

isTicking

Type: boolean

Description:

Whether monitoring has an underlying interval timer running or not.