• Executing a Ping
  • Crontab
  • Bash
  • Python
  • Node
  • PHP
  • Browser
  • PowerShell
  • Email
• Cron Syntax
• REST API

Summary

Each check in My Checks page has an unique "ping" URL. Whenever you access this URL, the "Last Ping" value of corresponding check is updated.

When a certain amount of time passes since last received ping, the check is considered "late", and WMIT Watchdog sends an email alert. It is a simple idea.

Executing a Ping

At the end of your batch job, add a bit of code to request your ping URL.

• HTTP and HTTPS protocols both are fine
• Request method can be GET, POST or HEAD
• Both IPv4 and IPv6 work
• It does not matter what request headers you send, or what you put in request body.

The response will have status code "200 OK" and response body will be a short and simple string "OK".

Here are examples of executing pings from different environments.

Crontab

When using cron, probably the easiest is to append a curl or wget call after your command. The scheduled time comes, and your command runs. If it completes successfully (exit code 0), curl or wget runs a HTTP GET call to the ping URL.

# m h dom mon dow   command
  8 6 *   *   *     /home/user/backup.sh && curl -fsS --retry 3 https://healthchecks.it.wm.edu/ping/83ee377e-555e-4d43-9336-1a7a6e4aa30d > /dev/null

With this simple modification, you monitor several failure scenarios:

• The whole machine has stopped working (power outage, janitor stumbles on wires, VPS provider problems, etc.)
• cron daemon is not running, or has invalid configuration
• cron does start your task, but the task exits with non-zero exit code

Either way, when your task doesn't finish successfully, you will soon know about it.

The extra options to curl are meant to suppress any output, unless it hits an error. This is to prevent cron from sending an email every time the task runs. Feel free to adjust the curl options to your liking.

Bash or a shell script

Both curl and wget examples accomplish the same thing: they fire off a HTTP GET method.

If using curl, make sure it is installed on your target system. Ubuntu, for example, does not have curl installed out of the box.

# using curl:
# (make sure it is installed on your system!)
curl --retry 3 https://healthchecks.it.wm.edu/ping/83ee377e-555e-4d43-9336-1a7a6e4aa30d

# using wget:
wget https://healthchecks.it.wm.edu/ping/83ee377e-555e-4d43-9336-1a7a6e4aa30d -O /dev/null

Python

# using urllib2:
import urllib2
urllib2.urlopen("https://healthchecks.it.wm.edu/ping/83ee377e-555e-4d43-9336-1a7a6e4aa30d")

# using requests:
import requests
requests.get("https://healthchecks.it.wm.edu/ping/83ee377e-555e-4d43-9336-1a7a6e4aa30d")

Node

var https = require('https');
https.get("https://healthchecks.it.wm.edu/ping/83ee377e-555e-4d43-9336-1a7a6e4aa30d");

PHP

file_get_contents('https://healthchecks.it.wm.edu/ping/83ee377e-555e-4d43-9336-1a7a6e4aa30d');

Browser

WMIT Watchdog includes Access-Control-Allow-Origin:* CORS header in its ping responses, so cross-domain AJAX requests should work.

// the server returns appropriate CORS headers so cross-domain AJAX requests should work:
var xhr = new XMLHttpRequest();
xhr.open('GET', 'https://healthchecks.it.wm.edu/ping/83ee377e-555e-4d43-9336-1a7a6e4aa30d', true);
xhr.send(null);

PowerShell

You can use PowerShell and Windows Task Scheduler to automate various tasks on a Windows system. From within a PowerShell script it is also easy to ping WMIT Watchdog.

Here is a simple PowerShell script that pings WMIT Watchdog. When scheduled to run with Task Scheduler, it will essentially just send regular "I'm alive" messages. You can of course extend it to do more things.

Invoke-RestMethod https://healthchecks.it.wm.edu/ping/83ee377e-555e-4d43-9336-1a7a6e4aa30d

Save the above to e.g. C:\Scripts\healthchecks.ps1. Then use the following command in a Scheduled Task to run the script:

powershell.exe -ExecutionPolicy bypass -File C:\Scripts\healthchecks.ps1

Email

As an alternative to HTTP/HTTPS requests, you can "ping" this check by sending an email message to 83ee377e-555e-4d43-9336-1a7a6e4aa30d@localhost

This is useful for end-to-end testing weekly email delivery.

An example scenario: you have a cron job which runs weekly and sends weekly email reports to a list of e-mail addresses. You have already set up a check to get alerted when your cron job fails to run. But what you ultimately want to check is your emails get sent and get delivered.

The solution: set up another check, and add its @hchk.io address to your list of recipient email addresses. Set its Period to 1 week. As long as your weekly email script runs correctly, the check will be regularly pinged and will stay up.

When Alerts Are Sent

Each check has a configurable Period parameter, with the default value of one day. For periodic tasks, this is the expected time gap between two runs.

Additionally, each check has a Grace parameter, with default value of one hour. You can use this parameter to account for run time variance of tasks. For example, if a backup task completes in 50 seconds one day, and completes in 60 seconds the following day, you might not want to get alerted because the backups are 10 seconds late.

Each check can be in one of the following states: