In simplest words, as put by Wikipedia, HTTP/2 is the second major version of the HTTP network protocol.
Earlier, in February 2015, Google had announced that they plan to remove support for SPDY in early 2016 and strongly encourage server developers to move to HTTP/2 and ALPN.
Now,
What does HTTP/2 has to offer?
In a nutshell, better speed, better security, better UX.
In a little detail, Akamai puts the benefits of HTTP/2 pretty well.
Multiplexing and concurrency: Several requests can be sent in rapid succession on the same TCP connection, and responses can be received out of order — eliminating the need for multiple connections between the client and the server
Stream dependencies: the client can indicate to the server which of the resources are more important
than the others
Header compression: HTTP header size is drastically reduced
Server push: The server can send resources the client has not yet requested
You will not need to change your websites or applications to ensure they continue to work properly. Not only will your application code and HTTP APIs continue to work uninterrupted, but your application will also likely perform better and consume fewer resources on both client and server.
Take A Demo
The Akamai Demo demonstrates the loading of their Akamai Spinning Globe via HTTP/1 and HTTP/2. The difference is actually amazing to see.
There has to be some shortcoming
There are few who don’t seem much impressed.
Author of Varnish, Poul-Henning Kamp, feels that HTTP/2.0 is really just a grandiose name for HTTP/1.2: An attempt to smooth out some sharp corners, to save a bit of bandwidth, but not get anywhere near all the architectural problems of HTTP/1.1 and to preserve faithfully its heritage of badly thought out sedimentary hacks.
Perhaps it would be too soon to make any predictions. Let’s see how it rolls out.
Will HTTP/2 replace HTTP/1.x?
As IETF HTTP Working Group answered in the HTTP/2 FAQ section, the goal of the Working Group is that typical uses of HTTP/1.x can use HTTP/2 and see some benefit. Having said that, we can’t force the world to migrate, and because of the way that people deploy proxies and servers, HTTP/1.x is likely to still be in use for quite some time.
Known Implementations of HTTP/2
This is a detailed document written by Daniel Stenberg describing HTTP/2 (RFC 7540), the background, concepts, protocol and something about existing implementations and what the future might hold.
