HTTP/2, originally named HTTP/2.0, is another revision of the HTTP network protocol after HTTP1.1. HTTP/2 is a binary protocol that supports multiplexing and header compression. It greatly improves web performance and reduces network latency. This topic describes the concepts, benefits, use scenarios, and configuration method of HTTP/2.


An SSL certificate is configured for the domain name. For more information, see Configure an SSL certificate.
  • If this is the first time you configure an SSL certificate, you must wait until the certificate takes effect before you can enable HTTP/2.
  • If you disable HTTP/2, the HTTP/2 settings are dimmed.
  • If you disable the SSL certificate after you enable HTTP/2, HTTP/2 is automatically disabled.

What is HTTP/2?

HTTP/2, originally named HTTP/2.0, is the latest version of HTTP. Compared with HTTP/1.1, HTTP/2 supports more features, including multiplexing, header compression, request prioritization, and server push. HTTP/2 provides optimized performance and is compatible with HTTP/1.1 semantics. HTTP/2 is supported by all major browsers such as Google Chrome, Microsoft Edge, Safari, and Mozilla Firefox.

Benefits of HTTP/2:
  • Binary encoding: Unlike the newline delimited plaintext HTTP/1.x protocol, all HTTP/2 communication is split into smaller messages and frames, each of which is encoded in binary format. The binary encoding mechanism makes HTTP/2 more extensible. For example, frames are introduced to transmit data and instructions.
  • Multiplexing: HTTP 1.x requires sprites and multiple domain names to improve performance because browsers limit the number of requests to the same domain name. If a large number of resources on a page are requested by clients, head-of-line blocking (HOL blocking) may occur. If the number of requests reaches the upper limit, the requests must wait in the queue because only one request can be delivered at a time per connection. HTTP/2 is the new framing layer, at which bidirectional streams (requests and responses) can be transmitted over the same TCP connection. Each stream has a unique identifier and headers based on which the stream is encapsulated between the client and server. This mechanism eliminates HOL blocking and improves transmission performance.
  • Header compression: Each HTTP message carries a large number of headers that describe the transferred resource and properties. To reduce the overhead and improve performance, HTTP/2 uses HPACK compression. HTTP/2 requires both the client and server to maintain and update an indexed list of header fields. This list is used as a reference to encode previously transmitted values by transferring index values. This improves the data transmission efficiency and performance.
  • Server push: Server push enables a server to send multiple responses to a single client. In addition to the response to the original request, the server can push additional resources to the client.

Enable or disable HTTP/2

  1. Log on to the Alibaba Cloud CDN console.
  2. In the left-side navigation pane, click Domain Names.
  3. On the Domain Names page, find the domain name that you want to manage and click Manage in the Actions column of the domain name.
  4. In the management pane of the domain name, click HTTPS.
  5. In the HTTP/2 section, turn on or turn off HTTP/2.