Learning HTTP/2

Chapter 5. The HTTP/2 Protocol

This chapter provides an overview of how HTTP/2 works at a low level, down to the frames on the wire and how they interact. It will help you understand many of the benefits (and problems) the protocol provides. By the end you should have enough information to get started with tuning and debugging your own h2 installations in order to get the most out of the protocol. For the brave who would like to go deeper into the protocol, perhaps for implementation purposes, RFC 7540¹ is an excellent place to start.

Layers of HTTP/2

HTTP/2 can be generalized into two parts: the framing layer, which is core to h2’s ability to multiplex, and the data or http layer, which contains the portion that is traditionally thought of as HTTP and its associated data. It is tempting to completely separate the two layers and think of them as totally independent things. Careful readers of the specification will note that there is a tension between the framing layer being a completely generic reusable construct, and being something that was designed to transport HTTP. For example, the specification starts out talking generically about endpoints and bidirectionality—something that would be perfect for many messaging applications—and then segues into talking about clients, servers, requests, and responses. When reading about the framing layer it is important to not lose sight of the fact that its purpose is to transport and communicate HTTP and nothing else.

Though the data layer ...