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Performance optimization in an HTTP/2 world

A revolution is currently going on in the underpinnings of the web. HTTP, the protocol your browser uses to connect to your site, has a new version: HTTP/2. This is not something that should concern the average user, but for web developers, it changes how we do performance optimization entirely. In this short article, I want to explain what performance optimization best practices you can do away with, and why.

What changed?

The most important thing you should know about the new HTTP/2 is that it no longer requires a new request for each file. This is the modification that makes our performance optimization guidelines change so drastically. In the HTTP1 / HTTP/1.1 world, it’d be faster to combine JS & CSS files and even images, so there would be fewer requests between browser and server. In the HTTP/2 world, this type of optimization is no longer needed and can even become counterproductive.

Can I use this already?

The answer is, fairly simply: yes. If your site is running on HTTPS, then all major current browsers support HTTP/2. You or your hosting company might have to change your server configuration to make sure it supports HTTP/2, but that’s it. Some older browsers might not be able to use it, but your site would still work for them.

So I can use HTTP/2, but should I?

Yes, you should use HTTP/2! It’s a lot faster than old fashioned HTTP1, and when you set it up well, most of your visitors will benefit hugely.

Does HTTP/2 mean I don’t need a CDN?

Even with HTTP/2 you still need a CDN. A CDN delivers content a lot faster than your average server ever will, so your site would still benefit enormously from having one. Every proper CDN will already support HTTP/2.

Performance best practices that changed

The following performance best practices are no longer needed with HTTP/2 and should be done away with:

Google PageSpeed and HTTP/2

Unfortunately, Google’s PageSpeed tool and many other web performance testing tools are rather slow in their adoption of HTTP/2. They should be changing their guidelines. If a simple HTTP/2 test shows you that a site is capable of using HTTP/2, quite a few of the site speed suggestions are moot. Their documentation speaks of “networking round trips” that simply, in an HTTP/2 environment, don’t happen.

There are people at Google that understand this, of course. This presentation by Ilya Gregorik in 2015 already shows all of that.

Read more: ‘Site speed: tools and suggestions’ »