What’s the Difference Between Website Availability and Performance Monitoring ?

In this post I’ll explain the difference between website availability (learn more) and performance monitoring (learn more) and help you to decide which one is most appropriate for your website.

Availability Monitoring

The availability monitor performs either a HTTP GET or POST request for the URL to be tested and checks the HTTP response code and optionally the returned html to see if the request was successful. If the request returns with a status code other than 200 (OK) then its considered an error. Additionally the monitor can be configured to check for a specific text string in the returned page content. When performing an HTTP POST the monitor can be configured to include data with the request simulating entering form data on the page.

This type of test confirms your URL can be resolved via DNS and that the web server is returning  html content. Additionally the test provides basic performance data for downloading the base page html. The performance information returned from this test however does not correlate with the time it would take to download the page in a user’s browser as it’s only getting the base html page and not the other objects referenced on the page such as image, script and css files.


HTTP Get - Small


To get a better idea of the page performance from a user’s perspective and also to confirm that all the page’s contents are accessible, you need to use a Performance monitor.

Performance Monitoring

The Performance monitor builds on the functionality of the Availability monitor and in addition to getting the page html it also downloads all the referenced content such as CSS stylesheets, flash content, images and javascript files. This better approximates the page download time as seen by a user’s web browser.

The Performance Monitor provides several benefits over Availability monitoring including:

Better Performance Reporting - Because this monitor downloads all the content referenced by the page, it provides a better idea of how long your entire page is taking to download and display in a user’s browser.

Bottleneck detection - Using elkMonitor reports you can see how your page’s content is affecting the total download time. This can be important when you have content referenced from other servers or sites which if slow can degrade your customer’s browsing experience.

Detect broken content links -Broken links in your page can seriously impact the  user’s experience and the functionality of your page.




Which one is right for me ?

For very simple web pages an Availability monitor can be sufficient to alert you to server failures and basic performance issues. For business critical websites, Performance monitoring is a better solution as it can detect problems with components on the page as well as providing a more detailed look at your page performance from a user’s perspective.