There are a number of reasons why the original HTTP required revision. Though HTTP/1.1 has served the Web well for more than 15 years, its age began to show. Page loading is more resource intensive than ever and ultimately inefficient with HTTP/1.1 due to the need to use multiple TCP connections to issue parallel requests - this causes TCP congestion and high overhead, not to mention performance problems. Major changes with HTTP/2 allow for a single TCP connection for parallelism, as well as header compression to reduce overhead.
Use this guide to configure your Plesk-managed sites to use HTTP/2.
Google Chrome: A policy update for the Chrome web browser that was released in May/2016 removes support for NPN. This means that many Chrome users are seeing sites default back to HTTP/1. For Media Temple DVs managed with Plesk, support for HTTP/2 over Chrome is largely dictated by which version of CentOS you are using.
STEPS FOR ENABLING HTTP/2
1. Begin by making sure that you're using Plesk 12.5 (update #28 and above) and that it's updated. To update Plesk, use the update tool found in Tools & Settings >> Updates and Upgrades.
2. If you haven't done so, purchase and install an SSL. An SSL significantly increases the security of your site, and all browsers currently require one when using HTTP/2. You may also easily install a free SSL using the Let's Encrypt extension for Plesk. Instructions are found here. Sites that do not have an SSL enabled will default to using HTTP1.1. Media Temple SSL certificates offer a one-click domain-ownership verification option for domains using Media Temple DNS servers and also provide a one-click installation option for Plesk.
3. Verify that your version of Nginx is 1.9.14 or later and that it is running.
listen escapedAddress . ':' . $OPT['frontendPort'] . ($OPT['default'] ? ' default_server' : '') . ($OPT['ssl'] ? ' ssl ' : '') ?>;
listen escapedAddress . ':' . $OPT['frontendPort'] . ($OPT['default'] ? ' default_server' : '') . ($OPT['ssl'] ? ' ssl http2' : '') ?>;
/usr/local/psa/admin/bin/httpdmng --reconfigure-all service nginx restart