This post was originally published on the Rigor Web Performance blog.
Every day Rigor robots make 1.5mm visits to over 350,000 web pages and load 23mm assets in browsers from around the world. Because of the large amount of data that we sift through each day, we are able to detect many outages that occur on the internet in real time. Yesterday we saw a sizable outage across many of our customer and research accounts.
In all, the New Relic outage lasted nearly two full hours and caused significant UX problems for end users. This got me thinking about the two blogs I wrote in December describing the benefits and shortcomings of RUM and how it complements synthetic monitoring.
One of the key differentiators that I failed to mention in these blogs between RUM and Synthetics is the external nature of Synthetics. Despite all of the benefits of RUM, loading any external content on your site has risks. Unlike RUM, Synthetic monitoring is completely external and does not require any client-side installation or the insertion of a web tag. As the New Relic outage so clearly illustrated, RUM at its worst can be the source of serious performance problems and at its best is still yet another asset that needs to be loaded by your users at a time when web pages are already slowing and growing at an alarming rate.