SPDY && HTTP 2.0 – Server hint

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SPDY && HTTP 2.0 – Server hint

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SPDY && HTTP 2.0

The new web protocols

Why do we need them?

HTTP versions

  • HTTP/0.9 (1991)
  • HTTP/1.0 (1996)
  • HTTP/1.1 (1997, 1999)
The Internet was done so well that most people think of it as a natural resource like the Pacific Ocean, rather than something that was man-made. When was the last time a technology with a scale like that was so error-free? The Web, in comparison, is a joke. The Web was done by amateurs.

- Alan Kay

HTTP/1.0

Persistent connections not default

Persistent connection

HTTP/1.0

New header introduced:

Connection: Keep-Alive

HTTP/1.1

Persistent connections default

HTTP pipelining

HTTP pipelining

HTTP pipelining

Only enabled by default in Opera

Still only FIFO, no true multiplexing

More HTTP performance issues

Headers are not compressed (~0.7kB)

Headers are re-sent a lot

How to reach better performance?

Developers - Use several domains

Browsers - 6 connections per domain

SPDY

Developed by Google

Aimed to reduce page load time by 50%

Minimize deployment complexity

Improve web security

Does not replace HTTP

How does it work?

Multiplexing - only one connection

Compressed headers

Prioritization

Only new/changed headers

Server push/hint

Eliminate redundant headers

User-Agent, Host, and Accept-headers are static

Other headers are rarely changed

Server push

Data is sent to client without being requested

X-Associated-Content header

Example index.html

<html> 
  <head>
    <title>My dog</title>
    <link href='main.css' type='text/css' rel='stylesheet'>
  </head>
  <body>
    <img src='dog.jpg'>
    <script src='main.js'></script>
  </body>
</html>

Without server push (HTTP/1.1)

Server push

Server push

Vastly enhances page-load for first-time visitors

Works best for non-cached resources

Redundant data if resource is cached

Server hint

Server suggests specific resources

X-Subresources header

How web caching works

  • Cache-Control: max-age=120
  • If fresh in cache - everything is fine
  • If not - ask server if modified
  • 304 - not modified, no body
  • 200 - indeed modified, full response

Without server hint

Server hint

Server hint

Better option for returning visitors

Works best for cached resources

Performance improvement

27-60% without SSL

39-55% over SSL

Very good for high packet loss rate

Good for high RTT

SPDY issues

SSL handshakes

Worse perfomance when connection is lost

Harder to implement

Browsers with SPDY

Chrome

Firefox

Opera

Servers with SPDY

Jetty

Apache

nginx

Google?

Websites using SPDY

gmail.com

wordpress.com

twitter.com

facebook.com (will soon support)

Want to know if you use it?

chrome://net-internals/#events&q=type:SPDY_SESSION%20is:active

HTTP/2.0

Under development by IETF's HTTPbis working group

Targeting 2014 for release

Protocols that are considered:

SPDY

Microsoft's HTTP Speed+Mobility

HTTP/2.0

Initial draft Nov 2012 - straight copy of SPDY

SPDY is just something to start with

Q&A

johan.lundahl@jayway.com