HTTP/2 Update

Wednesday October 26, 2016

I wrote about the next version of the HTTP protocol 18 months ago. Since then, HTTP/2 has gained significant traction, but not without generating some controversy along the way.


Perhaps the biggest question lingering over HTTP/2 relates to real-world performance benefits. A demonstration comparing the time it takes to load a website over HTTP/1.1 without SSL/TLS versus HTTP/2 (which only works in browsers over HTTPS) has been criticized for being unrealistic. It loads 360 unique images, a scenario that highlights the strengths of HTTP/2’s new design. The criticism comes from the fact that the average web page only loads around 100 objects (images, style sheets, etc.), and is often optimized for HTTP/1.1 using techniques that reduce the effectiveness of the HTTP/2 mechanisms.

The transition to HTTP/2 poses a performance challenge because websites may need to be de-optimized for HTTP/1.1 to take full advantage of HTTP/2. Common techniques such as combining files or images (sprites) and domain sharding – where a web page is loaded from multiple domains – are designed to reduce the number of connections to a single site. Since the majority of Website visits still occur over HTTP/1.1, it’s too soon to take these steps to eke the last bit of performance out of HTTP/2.


In a recent report published by security vendor Imperva, HTTP/2 was shown to be vulnerable to both old and new attacks. The report concludes that HTTP/2 implementations are young and as with any new software, vulnerabilities will be found. Yahoo! Researchers have also published similar findings and conclusions. As we will see, these concerns don’t appear to be slowing adoption.

Browser adoption

Just about every major browser now supports HTTP/2. If you’re using an up-to-date browser, it’s very likely that you’ve been using HTTP/2 for a while now when visiting some of your favorite websites.

Web server adoption

HTTP/2 is implemented in the current versions of all the major web servers including Apache, IIS, and NGINX. Many of the most popular CDNs also support HTTP/2, including Akamai and CloudFlare. is a good resource for more details on HTTP/2 support.

Website adoption

HTTP/2 is now supported by 10% of websites, up from just 1% a year ago. Adoption is strongest among the most popular websites, including Google, Facebook, and Twitter. It’s interesting to compare the adoption rate of HTTP/2 with IPv6, the newest version of the internet protocol that underpins HTTP. IPv6 became a standard almost 20 years ago and today is only used by 7% of websites.

HTTP/2 is still a relatively young technology, but the rate of adoption by web servers and browsers strongly suggests that it will become dominant. So what are you waiting for? Now is a great time to start planning HTTP/2 support for your website. Remember that browsers only support HTTP/2 over HTTPS, so you’ll need an SSL/TLS certificate to benefit.

This article was originally published by the "CA Security Council". In 2021 the CASC was restructred and renamed to the "Public Key Infrastructure Consortium" shortly "PKI Consortium".

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