Part of running your website every day is knowing that things are ok. Websites experies outages for all kinds of reasons, and indeed as the complexity of the website increases, so too does the likelihood of something going wrong. Outages comes in all shapes and forms, unreachable DNS, 3rd party scripts misbehaving, failing AJAX calls, buggy javascript are just a few of the reasons. The symptoms can be truly diverse and more often than not it is something we hadn’t thought of (otherwise we would have a code path handling that case, right, right? ...read more

Debugging frontend problems should be simple. The reality is it is not always straightforward. It’s a potentially stressful exercise, given that diagnosis usually happens because of an outage of sorts. Outages mean users aren’t happy, or we’re losing money or users, or both. Okay, so we know we’re stressed. Now we have to work with a mix of system familiarity, crossed with a logical, often robotic, exercise of looking for clues and excluding suspects until a root cause is found. ...read more

tl;dr Nock overrides http(s).request functions, which needs to be done before other code stores a reference to it. We ran into an issue where Nock wasn’t recording api calls to a new service dependency we introduced into the BytesMatter codebase. The solution eventually turned out to be quite straightforward, but investigating it taught us that sometimes code subtleties mean that tools are not always as straightforward to use as the “copy-paste” tutorials suggest. ...read more

Before answering the question “How does real user monitoring work?” let’s first make sure we have a baseline understanding. Real User Monitoring and Synthetic Tooling Broadly speaking, when monitoring or measuring websites there are two types of approaches to take: Synthetic Tools Real User Monitoring Synthetic tools will programatically measure aspects of your site. These tools can be set up to run ad-hoc or ongoing depending on your requirements. ...read more

Let’s talk about performance bounce. tl;dr performance bounce is about users, single-number summaries (such as core web vitals speed index) are about seo ranking and benchmarking. These two concepts have overlap, but need to be separated. Beyond the 3 second rule The axiom that the likelihood of bounce increases beyond the 3 second mark has driven web performance into the business domain. Like every good movement, performance needed a starting point, and that was it. ...read more

This is a quick summary of a caveat of cross-origin resource sharing (CORS) when measuring performance of ajax requests using performance resource timings in the browser. To be clear in this article we will unpack slightly some of the information from Mozilla’s documentation on the subject. Why? While it contains the root cause it does not spell out the consequence, which hopefully we’ll do here. Resource Timing API wait what?! The rise and influence of performance measuring and monitoring across the discipline of web engineering has meant the respective tooling has come a long way too. ...read more

This is part 2 in a series about diagnosing website issues. Hopefully it gives us a framework to constructively and efficiently work through website outages or issues instead of working in a state of stress or panic. Thanks to Part 1, we know what it means to be in an outage. Everyone knows their place and we’re ready to figure out what on earth is going on. Now, obviously you’re not ACTUALLY reading this in the middle of an outage. ...read more

Let’s start with an assertion: Web performance is important. You agree with that and that’s why you’re here. Both real user monitoring and synthetic web performance tooling offer ways to shed light on how your website is performing for your users. Which to use? Easy, they offer different views and are both important. A simple way to differentiate is tools measure and evaluate, and monitoring tracks trends and deviations. If I may insert a pedantic opinion here, the former is best suited to build time and the latter for your production website. ...read more

This is part 1 of a series. As engineers we love building software. We love releasing software. We love seeing our software helping people. Diagnosing Website Issues is not always the first thing that comes to mind if we think about what we do day to day, but it is a real and critical part of our jobs. Unfortunately, sometimes things go wrong. Sometimes wrong is “just a bit wrong”. Those cases that can generally be filed under bug - fix later. ...read more