HTTP/2 is a new version of HTTP. Here’s what you need to know:

A lot isn’t changing

All the methods, status codes, request/response bodies, and headers mean exactly the same thing in HTTP/2.

before (HTTP/1.1):

method: GET  
path: /cat.gif  
headers:
- Host: examplecat.com  
- User-Agent: curl  

after (HTTP/2):

method: GET  
path: /cat.gif  
authority: examplecat.com  
headers:  
- User-Agent: curl

one change:
Host header => authority

HTTP/2 is faster

Even though the data sent is the same, the way HTTP/2 sends it is different. The main differences are: - It’s a binary format (it’s harder to tcpdump traffic and debug) - Headers are compressed - Multiple requests can be sent on the same connection at a time

before (HTTP/1.1):
→ request 1
response 1 ←
→ request 2
response 2 ←

after (HTTP/2):
→ request 1
→ request 2
response 2 ←
response 1 ← (out of order is ok)
(one TCP connection)

All these changes together mean that HTTP/2 requests often take less time than the same HTTP/1.1 requests.

Sometimes you can switch to it easily

A lot of software (CDNs, nginx) let clients connect with HTTP/2 even if your server still only supports HTTP/1.1.

1. Firefox to CDN: HTTP/2 request
   
2. CDN to your server: HTTP/1.1 request
3. your server to CDN: HTTP/1.1 response
4. CDN to Firefox: HTTP/2 response