HTTP 2.0 is coming, be ready



Ca va changer beaucoup de choses … certes, son adoption massive n’est pas pour tout de suite, mais voici en résumé les optimisations qu’il faudra conserver VS celles qu’il faudra abandonner : en rouge celles qui concernent les sites média telles que les nôtres

Optimize the content being served to the browser:

  • Minimizing JavaScript, CSS and HTML files
  • Removing redundant data from images
  • Optimize Critical Path CSS
  • Removing the CSS which is not needed on the page using tools like UnCSS before to send the page to the server
  • Properly specifying ETag to the files and setting far future expires headers
  • Using HTML 5 offline to store already downloaded files and minimize traffic on the next page load

Optimize the server and TCP stack:

  • Check your server and be sure the value of TCP’s Initial Congestion Window (initial cwnd) is 10 segments (IW10). If you use GNU/Linux, just upgrade to 3.2+ to get this feature and another important update – Proportional Rate Reduction for TCP
  • Disable Slow-Start Restart after idle
  • Check and enable if needed Window Scaling
  • Consider to use TCP Fast Open (TFO)

(for more information check the wonderful book “High Performance Browser Networking” by Ilya Grigorik)

We may consider to remove the following “optimizations”:

  • Joining files – nowadays many companies are striking for continues deployment which makes this challenging – a single line of code change invalidates the whole bundle. Also, it forces browser to wait until the whole file arrives before to start processing it
  • Domain sharding – loading resources from different domains in order to avoid browser’s limit of connections per domain (usually 6) is the first “optimization” to be removed. It causes retransmissions and unnecessary latency
  • Resource inlining – prevents caching and inflates the document in which they are being stored. Instead, consider to leave CSS, JavaScript and images as external resources
  • Image sprites – the problem with cache invalidation is present here too. Apart from that, image sprites force browser to consume more CPU and memory during the process of decoding the the entire sprite
  • Using cookie free domains


HTTP has been in use by the World-Wide Web global information initiative since 1990. However, it is December 2014 and we don’t have anymore simple pages with cross linked HTML documents as it used to be. Instead, we have Web applications, some of them very heavy and requiring a lot of resources. And unfortunately, the version of the HTTP protocol currently used – 1.1, has issues.

HTTP is actually very simple – browser sends request the server, server provides the response and that is it. Very simple, but if you check the chart below you’ll see that there is not only one request and one response, but multiple requests and responses – about 80 – 100 and 1.8MB of data:

Now, imagine we have a server in Los Angeles and our client is in Berlin, Germany. All those 80-100 requests should travel from Berlin to L.A. and then get back. That is not fast – for example, the roundtrip time between London and New York is about 56 ms. From Berlin to Los Angeles it is even more. And as we know, first page load is latency bound; latency is the constraining factor for today’s applications.



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