Pacemaker

Basic health checks for web applications.

Install

$ git clone https://github.com/Lapixx/Pacemaker.git
$ cd Pacemaker
$ npm install

API

Pacemaker.create()

The Pacemaker package exports a single create() method to initialise a new Pacemaker instance:

const pacemaker = require("pacemaker");
const pm = pacemaker.create();

Once you have a new instance, you can use the following methods to control behaviour:

pm.interval(minutes)

Sets the interval of performing health checks on your endpoints.

pm.monitor(url)

Adds a new endpoint to check to your pacemaker instance. You can either provide a URL string, or an options object with the following properties:

url (string): The URL to check
body (regex): A regular expression to verify that the loaded page is correct (optional)
cert (boolean): Set to false if you want to ignore SSL certificate warnings (optional)

pm.notify(onError, onRevive)

Define handlers that get triggered when one of your endpoints goes offline, or when it comes back online again.

onError() gets called the when an endpoint becomes unavailable, and receives 3 parameters:

endpoint: The endpoint that is failing (either string or object, depending on what you provided in monitor())
error: The error code
details: Additional details to the error

Errors are defined in Pacemaker.Errors, and can be of either of 3 types:

CONN_ERR: Failed to connect to the host. details includes the full error object.
HTTP_ERR: The server returned a non-200 status code. details includes the returned status code.
BODY_ERR: The page did not match the regex you provided. details includes the retrieved contents.

onRevive() gets called when an endpoint went offline, and is now back online.

Take note that onError only gets called the first time an endpoint goes offline, until it becomes reachable again.

pm.start()

Start performing health checks on your endpoints.

pm.stop()

Stop performing health checks on your endpoints.

Full example:

const pacemaker = require("pacemaker");

pacemaker.create()
    .interval(5)
    .monitor("https://www.example.com")
    .monitor({ url: "http://blog.example.com", body: /<title>example blog/ })
    .monitor({ url: "https://selfsigned.example.com", cert: false })
    .notify(
        (x, err, det) => console.log("Offline: " + (x.url || x)),
        (y) => console.log("OK " + (y.url || y))
    )
    .start();

tkers/Pacemaker