HTTP/2 is now available on Plesk 12.5. HTTP/2 (originally named HTTP/2.0) is the second major version of the HTTP network protocol used by the World Wide Web. Please take notice that HTTP/2 is supported for SSL sites only, so non-SSL sites will continue to work under HTTP/1.x. That’s a restriction of NGINX web server and web browsers. HTTP/2 support requires the Plesk 12.5.30 Update#28 being installed, as well as NGINX 1.9.14 (which is included in the update).

Login to your server via SSH under root and enable HTTP/2 support in Plesk using the following command line utility: on RedHat/CentOS:

#/usr/local/psa/bin/http2_pref enable

On Debian/Ubuntu:

#/opt/psa/bin/http2_pref enable

During the last step your NGINX web server will be tuned to use the TLS protocol with modern and secure ciphers, the whole web server configuration will be rebuilt, and all client’s sites with ‘SSL Support’ will be moved to HTTP/2.
Please check the output of the command to check for errors or warnings during the switch to HTTP/2.

If you wish to return to HTTP 1.x and disable HTTP/2, please use the following command:

#/usr/local/psa/bin/http2_pref disable