How Do Real User Monitoring (RUM) Tests Work?

RUM tests

Introduction to RUM Tests

RUM tests are a crucial monitoring tool for performance-oriented content delivery companies. While they are not exclusive to CDNs, they are important in measuring real-world performance to/from a variety of destinations: whether it is a website’s load time, or latency to an edge node, RUM tests (or Real User Monitoring) measure application performance for both analytics and status monitoring (e.g. seeing degraded performance with users in a specific region due to, say, a fibre cut).

The Difference Between Real User Monitoring (RUM) and Synthetic Tests

RUM tests are fundamentally different from synthetic tests. The latter generally requires a set of servers, owned and run by a single entity. In other words, synthetic testing can measure performance almost instantaneously, but they typically don’t represent a real-world experience, which RUM tests show.

Unfortunately, even with all the listed benefits of RUM testing, the information is received as users view a page, rather than instantaneously. Also, there are many factors that cannot be measured that can affect a RUM test:

• The user's internet connection (Wi-Fi, a LTE hotspot, wired connection)
• Device (an old Android phone will load a page slower than a modern iPhone)
• Weather conditions in the user's region

Essentially, RUM tests should be paired with synthetic tests for the most accurate results.

More Examples of Real User Monitoring (RUM) Testing

• Latency to other servers (using embedded JS), through ping
• Application performance (whether or not, say, an update has improved or made performance to a tool worse)
• Issues with a page’s programming (measuring if a user has to wait, ex. 10 seconds before they see any semblance of a polished page)
• How a user experiences and uses an application (this is typically done to improve UI/UX; positioning of certain buttons or fixing hard-to-read links)

A real RUM test

As hinted previously, there is a simple reason why RUM tests shouldn’t be an exclusive form of testing: the tests can be unreliable due to a variety of factors on a user’s device and they may not show the full reason a user experiences poor performance.

RUM tests can be very simple. Here's one written in JS (with jQuery):

$(document).ready(function() {
  var startTime = (new Date()).getTime();
    $(".dummy").load("pageToMonitor/", function(resp, status, xhr){
    if(status == "success") {
  	var loadTime = (new Date()).getTime() - startTime;
	// Send loadTime to server and capture page speed
    } else if (status == "error") {
  	console.log("An error occurred: " + xhr.statusText);
    }
  });
});

The code above waits for a page to fully load, then sends a test request to pageToMonitor/ and forwards the result back. The testing data is generated completely on a user’s device.

Conclusion

RUM testing is an incredibly valuable tool for monitoring users’ experiences. In the case of a CDN, such as bunny.net, RUM monitoring (even when provided by 3rd party services) offers valuable insight to real world changes in network performance compared to synthetic testing servers located in a well-connected datacentre.