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CloudFlare’s Impact On The HTTP/2 “Universe”


5 min read

CloudFlare released HTTP/2 support for all customers on December 3rd, 2015. Now, two months later, it's time to take a look at the impact of this release on the HTTP/2 "universe" and also at what has changed from a HTTP/2 vs. SPDY vs. HTTP 1.1 traffic ratio perspective.

HTTP/2 Usage

Previously, we showcased browser market share data from our own website. Using these numbers, we predicted the ratio of HTTP/2 traffic that we expected to see once enabled. Now, we can compare this original data set with updated data from the last 48 hours.

Below is the market share of HTTP/2 capable browsers that we saw on our website during a 48 hour period. The first one was before our HTTP/2 launch, the other one was last week. Both data sets were pulled from Google Analytics, and user agents were analyzed for HTTP/2 support.

HTTP/2 capable browser Global Market Share Late Nov 2015 Global Market Share Late Jan 2016
IE 11 on Windows 10 0.14% 0.34%
Edge 12, and 13 0.35% 0.48%
Firefox 36 - 45 5.09% 11.05%
Chrome 41 - 49 15.06% 38.86%
Safari 9 0.91% 2.69%
Opera 28 - 34 0.57% 0.78%
Safari for iOS 9.1 1.07% 0.94%
Opera 30 for Android 0.01% 0.00%
Chrome 46 - 48 for Android 3.59% 1.60%
Firefox 41 - 44 for Android 0.01% 0.00%
Total 26.79% 56.74%

Since November, the number of browsers visiting that support HTTP/2 has more than doubled. In particular, notice how the market share of Chrome and Firefox versions that support HTTP/2 increased dramatically within the last 2 months.

The reason for this is, that even with Auto-Update functionality in modern browsers, new versions are not adopted instantaneous. We had documented the release of iOS 9, which is an example for a quite swift adoption.
Looking at the challenges around the SHA-1 deprecation, we can see that some really old OS and browser version are still around.

Keep in mind that we still see a larger number of non-browsers that don’t fall into any of the above buckets on our edge network. This is due to bots, crawlers, scrapers, and the like. The numbers above represent typical website traffic after it has been sanitized by CloudFlare.

Real-Life Numbers

With the promising browser market share data above, we can now compare the ratio of traffic served via the different HTTP versions on

Again, contrast the data from around our release in December to the current data.

Protocol Version Percentage of Hits December 2015 Percentage of Hits February 2016
HTTP/1.x 19.36% 17.29%
SPDY/3.1 57.02% 29.79%
HTTP/2 23.62% 52.93%

The great news: the HTTP/2 traffic ratio has indeed more than doubled on since we rolled out HTTP/2.

Nevertheless, we are still serving a large portion of traffic over SPDY, mostly due to older versions of Chrome.
Therefore it was a good choice to keep supporting this protocol version.

Number of HTTP/2-Powered Websites

So far, we have looked at what an individual HTTP/2 enabled site on CloudFlare could expect to see with regards to traffic and different browser versions. Let’s shift gears a bit and have a look at how many websites we have actually enabled with HTTP/2 so far:

The website is a great tool for finding an answer to this question. It is created and maintained by researchers at Telefónica Research, Case Western Reserve University, and Carnegie Mellon University, and provides an overview of how many websites from the Alexa 1M list are enabled with HTTP/2.

The website differentiates between:

  • Announced Support: Sites indicate which application-layer protocols they support using NPN/ALPN. If a site indicates HTTP/2, it is considered as "Announced Support."

  • Partial Support: Some sites that announce HTTP/2 support, but immediately downgrade the connection to HTTP 1.1 if a client makes a request using HTTP/2. If a site responds using HTTP/2, even just to return an error page or redirect, this is classified as partial support.

  • True Support: If a site actually serves page content using HTTP/2, even if some embedded objects are still served over HTTP 1.1, this is called true support.

In this post, we will only focus on websites with "True Support"—since that’s what you get with CloudFlare—and will ignore the other two metrics.

Looking at the HTTP/2 adoption curve for the Alexa 1 million shows quite an interesting picture:

graph of http/2 support over time

You can see a sharp increase of domains with "True Support" in December 2015, bringing the number of domains with “True Support” from 14,017 (December 1st, 2015) to 75,288 (December 31st, 2015).

According to, 58,591 of these domains run through CloudFlare. That means CloudFlare more than quadrupled the number of HTTP/2 sites with the December 2015 release.

We’d like to give a big shout-out to the team of They worked with our engineers to update their measurement method to include the Server Name Indication (SNI) TLS extension when they probe sites for HTTP/2 support. By doing so, the site is able to identify all CloudFlare-powered sites. You can see this measurement change kicking in within the above graph at the sharp increase from 24,947 domains to 74,271 domains.

HTTP/2 Market Position

Another website measuring the adoption of HTTP/2 on the server side is W3 Techs. While the graph generated by W3 Techs for HTTP/2 adoption is much more coarse grained on the time axis, the increase of HTTP/2 enabled websites due to CloudFlare is nevertheless clearly visible.

graph of http/2 traffic over time (coarse)

With our wide support of HTTP/2 for all CloudFlare customers, we have also helped to improve the market position—with regards to popularity and traffic—of HTTP/2 close to that of SPDY.

HTTP/2 vs SPDY market share

Want to help us grow our software engineering team and increase our protocol support? Check out our available roles.

Enabling HTTP/2

As a reminder, if you are a customer on the Free or Pro plan, there is no need to do anything at all. Both SPDY and HTTP/2 are already enabled for you. With this improvement, your website’s audience will always use the fastest protocol version when accessing your site over TLS/SSL.

Customers on Business and Enterprise plans can enable HTTP/2 within the "Network" application of the CloudFlare Dashboard. In the last two months, the web still hasn't exploded while running HTTP/2. With that in mind, it's probably safe for you to head over an enable HTTP/2 now. You will be in great company with many other sites.

enabling HTTP/2 in the CloudFlare dashboard

If you are not yet a customer of CloudFlare, sign up now and you’ll be able to leverage HTTP/2 within a few minutes.

Stay tuned for more additions to our HTTP/2 capabilities!

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