Website Uptime Monitoring: The Basics
There are lots of website uptime monitoring services out there but all the components you need to build your own website monitoring tool can be found in good ole’ Microsoft VBScript.
Stop laughing, I’m not kidding!
In this article, I’ll share with you some scripts and tips I’ve used successfully in the past for monitoring website uptime even if your website is running in a complex load balanced enterprise environment which some of mine are.
VBScript Components for Uptime Monitor
Most people don’t know that VBScript can make Ajax HTTP calls but it can.
We will use VBScript’s ability to make Ajax HTTP calls to our website to see if it responds then put some simple logic around that response to log the results in a text/csv file.
It really is amazingly simple once you get all the code components together.
The ISWebSiteUp Function
The ISWebsiteUp function in my code example takes a URL string and makes an Ajax HTTP call to see if we get a HTTP code 200 or 404 returned meaning website loaded OK.
Once we get our 200 or 404 HTTP response code that, script returns true in the form of a text message box or if script times out you’ll get a false in an error message box.
You might be saying to yourself about now, what about the 404 response code for page not found. Yes, you might want to add some more code to handle that differently than a 2oo OK response but for this script, we just want to know if server is up. If we are pointing to a page at the root of a domain, we don’t typically get 404 errors in reality.
The Script Code
To use this code, copy it in to a text file and save it with a .vbs file extension for VBScript. Once you have the .vbs file, double click on it. You will see the message box with the message, “is up” or “is down”. A super simple example for our core application.
'isWebsiteUp: Takes String URL
'isWebsiteUp: Returns strMessage in Message Box
Function isWebsiteUp(strURL)
On Error Resume Next
Set http = CreateObject("MSXML2.ServerXMLHTTP")
'Set http = CreateObject("Microsoft.XmlHttp")
http.open "GET", strURL, False
http.send ""
'Only check for error of the HTTP Get request for 200 or 404 code returned. If any status is returned then the server is up
if http.responseText <> "" AND err.number = 0 then
'Commented out showing the response text. Use this for troubleshooting or exploring.
'msgbox(http.responseText)
isWebsiteUp = true
strMessage = "is up"
else
isWebsiteUp = false
strMessage = "is down"
end if
Set http = Nothing
msgbox(strURL & ":" & strMessage)
err.clear
End Function
call isWebsiteUp("https://www.google.com") What the Web Server Sees in the HTTP call: WinHTTPRequest User Agent
The VBScript Ajax HTTP call to the web server presents itself as a web browser asking for the home page.
In the server logs a server admin may see this “User Agent” in their logs.
Mozilla/4.0 (compatible; Win32; WinHttp.WinHttpRequest.5)
Script Errors & Blocked HTTP Calls
This script works out of the box. Google is the most open website in the world in terms of IPs that their servers accept traffic from as they are in the business of collecting data about everything including every system that connects to it.
Other web servers, like ones I run, may not be so forgiving. Many server admins use many tools at their disposal to filter HTTP request at various levels.
Here are some examples of tools Windows Server Admin have at their disposal to block or filter your script from connecting to their web servers.
Windows Server Admin Tools for Handling HTTP Traffic
- Firewall IP Restrictions (Window Server Admin)
- HTTP Response Filtering (IIS Application Server Admin)
- IP Restrictions (IIS Application Server Admin)
