Sentinel: Your Web-Performance Watchman

Moving CSS Wizardry onto HTTPS and HTTP/2

Written by on CSS Wizardry.

Table of Contents
  1. HTTPS
  2. HTTP/2
  3. Browser Support
  4. What Next

Hopefully by now, you should be able to read this article over HTTPS and HTTP/2. (If that link doesn’t work, please hit your back button and let me know!) I made the switch yesterday, and all being well the new DNS settings have propagated through. At some point soon I will begin forcing all HTTP traffic to HTTPS.

The site is still built with Jekyll and hosted on GitHub Pages, but it’s now fronted by Cloudflare who offer a plethora of performance-related services. I was only really interested in HTTPS because it allows me to use, among other things, HTTP/21, Brotli, and Service Worker (I’m not actually using the latter two yet, but now at least I can CSS Wizardry is now running on a simple Service Worker!), and when my buddy James tipped me off as to just how simple the process is, I got stuck in and got it done.

As an aside, I had some issues specific to my domain registrar (not GitHub or Cloudflare) which my very good friend Steve helped out with. He’s a very talented software and Ops engineer who managed to solve in minutes a problem that had troubled me all day. Thanks, Steve!


My site is completely static; it doesn’t take any user input, there is no logic or scripting, no database, so I didn’t feel like the need for HTTPS from a security point of view was all that pressing2. However, HTTPS is a prerequisite for a number of other technologies, and having a secure site—regardless of its content—is never a bad thing. More on the first bit in a moment, but for now I want to talk a little about security.

I imagine that although most users won’t have much of an understanding as to the technical implications behind a secure or a not-secure site (I’m hesitant to use the word insecure), they are becoming aware that there is such thing as security. With Google’s intent to mark certain webpages as insecure, and the general increase in awareness, users do know that secure websites are a thing. The implication, therefore, is that any site that isn’t explicitly marked as being secure must be insecure (whether that’s actually the case or not).

To this end, I think that HTTPS is as much an exercise in branding and trust as it is in security, and that it will steadily become more and more ubiquitous. This is only a good thing.

Further, HTTPS is required in order for certain other technologies to be utilised:

  • Brotli, an improved compression algorithm from Google, needs to run over HTTPS because of third parties (ISPs, proxies, etc.) infamously trying to recompress already compressed transfer. By preventing them getting at it in the first place, it means that they can’t try running gzip over a new, unknown content encoding (e.g. Brotli).
  • Service Worker absolutely needs to run over HTTPS, because it’s basically a man in the middle. We’re building a proxy that sits in between our users and our servers, so the need for security there should be pretty clear.


HTTP/2 (or H2, as it’s commonly referred to) is a vast, vast improvement on the HTTP/1.1 protocol that we’ve been using for almost two decades. It brings many benefits to both developers and users, but many of its best features are centred around performance:

  • Compressed headers: HTTP/1.1 sends its headers uncompressed, which creates a surprising amount of overhead. HTTP/2 reduces that by compressing the response headers as well as the response body.
  • Multiplexing: get around head of line blocking and lack of parallelisation by sending multiple assets asynchronously over the same TCP connection.
  • Server push: allows developers to send late requested assets preemptively.

A lot of HTTP/2’s additions will moot the domain sharding, concatenating, and inlining strategies we came up with as hacks, and will instead allow us to deliver faster experiences with simpler architectures: we can optimise assets all we like, but there is no denying that HTTP/2 gives developers an astounding performance boost right out of the box.

Currently I’m not making that much use of anything HTTP/2 offers me other than multiplexing and header compression (because I didn’t even have to lift a finger for those). My site is already pretty slim, and I’m serving so few assets that one could almost argue over-engineering, but one really great example of where I will benefit from HTTP/2 multiplexing is this relatively large list of images on the homepage.

Browser Support

Support for HTTP/2 is pretty good, and always improving. Servers capable of serving over HTTP/2 will also still deliver to HTTP/1.x clients, so nothing will break.

However, it might not be time for your company to switch over too. Unfortunately, HTTP/2 best practices become bad practices in HTTP/1.1, and HTTP/1.1 best practices become bad practices in HTTP/2. Optimising for one will be detrimental to the other, and it’s pretty hard to satisfy both camps.

Fortunately for me, looking at the data, over the past 24 months over 85% of CSS Wizardry’s traffic has come from a browser that supports HTTP/2. For me it’s pretty clear that using HTTP/2 is the right decision. Other companies (government, ecommerce, etc.) might not have quite such a clear cut view.

What Next

Next up, I can look at implementing I have now implemented a simple Service Worker to provide better caching strategies, as well as a simple offline page for users on poor or non-existent connections. I should also look into splitting up my CSS into more granular, individually cacheable chunks.

Unfortunately, given that I am still hosting on GitHub Pages, I am limited in how much I can implement. Things like enabling Brotli will have to be done by Cloudflare, and utilising Server Push would require access to server-level configuration. That stuff will have to wait, but I can probably manage without it whilst I’m serving up a flat-file website with such a small footprint in the first place.

With all of this said, despite HTTP/2’s clearly superior approach to optimising user experiences, there is still great need for fundamental performance knowledge within teams: optimising assets, structuring more elegant delivery, and building to support non-HTTP/2 environments are all still very important.

If you’d like any advice or help with any of the above, I am lining up performance consultancy work for Q2 onward. Get in touch.

  1. Interestingly, the HTTP/2 standard doesn’t define HTTPS as being mandatory, but almost all browser vendors have stated that they will only support HTTP/2 over a secure connection, which makes it pretty mandatory in practice. 

  2. I know, I know: there’s a lot more benefit to HTTPS than that. 

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Hi there, I’m Harry Roberts. I am an award-winning Consultant Web Performance Engineer, designer, developer, writer, and speaker from the UK. I write, Tweet, speak, and share code about measuring and improving site-speed. You should hire me.

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