SPDY

Andreas Bjärlestam 2012-05-30

SPDY quick overview• An evolution of HTTP• Developed by Google since 2009• Openly available spec

Why the hell would you want to replace HTTP?

HTTP is fantasticit has totally changed the world

but…

HTTP is over 20 years oldHTTP 1.1 is 12 years old

Webpages in 1999

Webpages in 2012

Mobile internet usagesource: svenskarnaoch internet 2011 https://www.iis.se/docs/SOI2011.pdf

This is how more and more of us consume the web…

Often it feels a lot like…

People no longer have patience to wait for slow pages

Web pages February 2012• www.facebook.com - ca 100 http requests• www.bostonglobe.com - ca 100 http requests• www.svtplay.se - ca 90 http requests• www.aftonbladet.se - ca 350 http requests source: http://httparchive.org/

What does it look like over thenetwork fetching 100 resources?

Can you spot the problem?

Its all synchronous

How come an advanced page like facebook.com loads in under 4seconds when its all synchronous?

Hacky optimizations CSS spritesbase64 images in data-urls CSS concatenation JavaScript concatenation

6 x HTTP connections HTTP/TCP HTTP/TCP HTTP/TCP HTTP/TCP HTTP/TCP HTTP/TCP

Domain sharding• www.bostonglobe.com - 59 connections• www.svtplay.se - 22 connections• www.aftonbladet.se - 118 connections source: http://www.webpagetest.org

What is the problem with this? Why not even more?

We kind of abuse TCPwhen we open more connections

2 connections per host recommended by HTTP 1.1 spec 6 connections in most browsers

and…

New TCP connections are slow

3 way handshake

On my macbook Ping 20ms ≈ 30ms to set up a connection On my mobile (3G)Ping 300ms ≈ 450ms to set up a connection

TCP Slow start HTTP/TCP HTTP/TCP HTTP/TCP HTTP/TCP HTTP/TCP HTTP/TCP

Bandwidth doesn’t matter much anymore Latency does

So… we need to utilize our TCP connections better

Don’t we break the web if we replace HTTP?

The semantics of HTTP is kept

HTTP -> SPDY GET GET PUT PUT HEADERS HEADERS POST POST … …Use of URLs Use of TCP Use of URLs Use of TCP

You can switch to SPDY with nochanges to your web application

SPDY runs over TCP and will not require upgraded network equipment

Example…

Designed with speed as primary goal

1 TCP connection HTTP/TCP

But it will be on fire! HTTP/TCP

SPDY is multiplexed

This is a typical HTTP session GET 200 OK GET 200 OK GET 200 OK

Multiplexing GET 1 GET 2 GET 3 200 OK 2 200 OK 3 200 OK 1

Stream priorities

SPDY is binary

Will be difficult to just fire up telnet and hack away

Every decent site will be encrypted and gzipped anyways

✗TLS/SSL is mandatory

Communication should be secure by defaultUsers should not have to care

Headers are compressed

Server Push

So is it worth it?

Google tested 25 of the “top 100” sites

Average speedup 39% - 55%

SPDY could make your life easierLess need for hacky optimizations like CSS sprites, fileconcatenations, domain sharding etc

Should I add SPDY support to my servers on Monday?

Probably not…

Implementations• Apache mod_spdy• Nginx – in roadmap• node_spdy – requires node.js 0.7• Netty• Jetty• more…

Browsers• Chrome (since version 6)• Firefox (since version 11, turned off by default)• Amazon silk

Others• Strangeloop• Akamai (Contendo)• F5 BIG-IP

Google• Support SPDY on most of their services• 90% of their SSL traffic is over SPDY

Amazon silk Silk SPDY SPDY HTTP TheBrowser Gateway Internet

The spec• Draft spec, version 4• IETF HTTPbis WG has started to work on HTTP2.0• SPDY has been submitted as input to HTTP2.0

Roundup• ~ 50% Faster page loads than HTTP• Backwards compatible with HTTP• Better utilization of TCP• Secured by default• Binary + compressed• Will likely be the base for HTTP2.0

Attributions• http://en.wikipedia.org/wiki/File:US_Robotics_56K_M odem_Front.JPG• https://www.iis.se/docs/SOI2011.pdf• http://www.flickr.com/photos/howi/6366423373/• http://www.flickr.com/photos/wwarby/5110037138/• http://www.flickr.com/photos/alicetragedy/497729529 8/• http://www.flickr.com/photos/koltregaskes/624914973 /in/photostream/

Backup slides

Alternatives

HTTP Pipelining• Not as effective as multiplexing• Hard to implement in browser• Opera is the only desktop browser that has a full implementation enabled by default• Android, IOS5 and Opera mobile browsers do some amount of pipelining• Not used by most proxies

Synchronous Pipelining Multiplexing GET GET 1 GET 1 GET 2 GET 2 200 OK GET 3 GET 3 GET 200 OK 200 OK 1 200 OK 2 GET 200 OK 2 200 OK 3 200 OK 3 200 OK 1 200 OK

SPDY

by Andreas Bjärlestam on May 30, 2012

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