the spdy protocol

SPDY

http reloaded

GOOGLE PROPRIETARY PROTOCOL (WILL BE) PART OF HTTP/2.0

HTTP Problems

• Single request per connection. Because HTTP can only fetch one resource at a time (HTTP pipelining helps, but still enforces only a FIFO queue), a server delay of 500 ms prevents reuse of the TCP channel for additional requests. Browsers work around this problem by using multiple connections. Since 2008, most browsers have finally moved from 2 connections per domain to 6.

• Exclusively client-initiated requests. In HTTP, only the client can initiate a request. Even if the server knows the client needs a resource, it has no mechanism to inform the client and must instead wait to receive a request for the resource from the client.

• Uncompressed request and response headers. Request headers today vary in size from ~200 bytes to over 2KB. As applications use more cookies and user agents expand features, typical header sizes of 700-800 bytes is common. For modems or ADSL connections, in which the uplink bandwidth is fairly low, this latency can be significant. Reducing the data in headers could directly improve the serialization latency to send requests.

• Redundant headers. In addition, several headers are repeatedly sent across requests on the same channel. However, headers such as the User-Agent, Host, and Accept* are generally static and do not need to be resent.

• Optional data compression. HTTP uses optional compression encodings for data. Content should always be sent in a compressed format.

Source: http://dev.chromium.org/spdy/spdy-whitepaper

Web Requests Are Simple

• Open a connection

• Send a request

• Receive a response

• Done

Transfer per Page

Many Requests are a Pain

• Caching

• Domain Sharding

– Browser Limits

• Keep Alive

– Dedicated Connections

– Waste Ressources

• Pipelining

TCP Handshake

0ms 1) Host A sends a TCP SYNchronize packet to Host B

50ms 2) Host B receives A's SYN

50ms 3) Host B sends a SYNchronize-ACKnowledgement

100ms 4) Host A receives B's SYN-ACK

100ms 5) Host A sends ACKnowledge

150ms 6) Host B receives ACK.

• With a Ping of just 50ms, this takes us 150ms

Initial window

• Congestion Control Mechanism

• Avoid overloading clients

• Each ACK of the client increases window

• RFC 3390

– Increasing icwnd

– Small Resonses are complete without ACK

– Avoid the ACK RTT

Pushing over http

• Push === Long Polling

• Consumes one connection on clients

• On server

– Used to be expensive to hold

– Modern servers have evented I/O

• WebSockets

Headers

Accept text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8

Accept-Encoding gzip, deflate

Accept-Language de-de,de;q=0.8,en-us;q=0.5,en;q=0.3

Connection keep-alive

Cookie

__utma=40497137.1800912468.1315901303.1328525769.1328537171.234; __utmz=40497137.1326462670.198.110.utmcsr=twitterfeed|utmccn=blogfeed_de|utmcmd=twitter; wp-settings-3=editor%3Dhtml%26m0%3Do%26m1%3Do%26m2%3Do%26m3%3Dc%26m4%3Do%26m5%3Do%26m6%3Do%26m7%3Do%26m8%3Do%26m9%3Do%26m10%3Do%26m11%3Do%26align%3Dcenter%26imgsize%3Dfull%26urlbutton%3Dnone%26hidetb%3D0; wp-settings-time-3=1328519940; __utma=162617902.1417890302.1315914276.1328537194.1328541774.63; __utmz=162617902.1328537194.62.41.utmcsr=blog.codecentric.de|utmccn=(referral)|utmcmd=referral|utmcct=/; wp-settings-time-81=1321966374

Host blog.codecentric.de

User-Agent Mozilla/5.0 (Windows NT 6.1; WOW64; rv:10.0) Gecko/20100101 Firefox/10.0

http://blog.codecentric.de/

Headers

http://www.codecentric.de/files/2012/02/adlite.png

Accept image/png,image/*;q=0.8,*/*;q=0.5

Accept-Encoding gzip, deflate

Accept-Language de-de,de;q=0.8,en-us;q=0.5,en;q=0.3

Connection keep-alive

Cookie

__utma=162617902.1417890302.1315914276.1328537194.1328541774.63; __utmz=162617902.1328537194.62.41.utmcsr=blog.codecentric.de|utmccn=(referral)|utmcmd=referral|utmcct=/; wp-settings-3=m0%3Do%26m1%3Do%26m5%3Do%26m4%3Do%26editor%3Dhtml%26wplink%3D1%26align%3Dcenter%26imgsize%3Dfull%26hidetb%3D1%26m7%3Do%26m9%3Do; wp-settings-time-3=1326290899

Host www.codecentric.de

Referer http://blog.codecentric.de/

User-Agent Mozilla/5.0 (Windows NT 6.1; WOW64; rv:10.0) Gecko/20100101 Firefox/10.0

Content Compression

• Gzip is optional

• But generally best practice

LoadModule deflate_module /usr/lib/httpd/modules/mod_deflate.so

SPDY TO THE RESCUE

SPDY Solutions

• Allow many concurrent HTTP requests to run across a single TCP session.

• Reduce the bandwidth currently used by HTTP by compressing headers and eliminating unnecessary headers.

• Make SSL the underlying transport protocol, for better security and compatibility with existing network infrastructure. Although SSL does introduce a latency penalty, we believe that the long-term future of the web depends on a secure network connection. In addition, the use of SSL is necessary to ensure that communication across existing proxies is not broken.

• Enable the server to initiate communications with the client and push data to the client whenever possible.

Source: http://dev.chromium.org/spdy/spdy-whitepaper

Connection Multiplexing

• Single TCP Connection transports all requests

• TCP Handshake still exists

• Inital cwnd should be 16

Compression

• All data is compressed

• Includes headers

• Redundand data is removed

– User Agent of second request is known to be same as on first

SSL

• Not said to be a problem with HTTP

• SSL should be default

– But actually expensive

• SSL hides SPDY traffic, so that proxies don't break it

Pushing

• Long Lasting Connection By Design

• Send does not close the "request"

• Two flavors

– Server push

– Server hint

Compatibility

• SPDY is backwards compatible

• Uses Next Protocol Negotiation

– tools.ietf.org/html/draft-agl-tls-nextprotoneg-02

SPDY Support

Clients

• Chrome – On since 11

– Ice Cream Sandwich

• Amazon Silk – Kindle Fire

• Firefox – experimental in 11

– On in 12/13

Server

• Apache mod_spdy

• erlang-spdy

• node-spdy

• Netty 3.3.1 – Means JBoss

• Jetty 7.6.2

• Tomcat SPDY Connector

DEMO: MIGRATING PHP ON APACHE TO SUPPORT SPDY

PHP is not Threadsafe

• The way SPDY works is incompatible with non threadsafe implementations

– one connection one httpd worker

– But multiple requests

• Zend Threadsafe does not support some features (mysql!)

• Need to externalize it with cgi

mod_php to mod_fcgid + php

• yum install mod_fcgid

• vi /etc/httpd/conf/httpd.conf

• mv /etc/httpd/conf.d/php.conf /etc/httpd/conf.d/php.conf.bak

• vi /etc/httpd/conf.d/fcgid.conf

<Directory "/var/www/html">

Options Indexes FollowSymLinks ExecCGI

</Directory>

DirectoryIndex index.php

AddHandler fcgid-script .fcgi .php

DefaultInitEnv PHPRC "/etc/"

MaxRequestsPerProcess 1000

MaxProcessCount 10

MaxRequestLen 209715200

IPCCommTimeout 240

IdleTimeout 240

FCGIWrapper /usr/bin/php-cgi .php

mod_prefork to mod_worker

• Needs recompilation

• Luckily we have both already – httpd -V | grep MPM

– httpd.worker -V | grep MPM

• sudo vi /etc/init.d/httpd

httpd=${HTTPD-/usr/sbin/httpd.worker}

prog=httpd.worker

mod_ssl

• We need mod_ssl patched with NPN • yum install subversion curl gcc-c++

patch binutils make

• mkdir modssl; cd modssl

• svn export http://mod-

spdy.googlecode.com/svn/trunk/src/bu

ild_modssl_with_npn.sh

• ./build_modssl_with_npn.sh

• cp /root/modssl/mod_ssl.so

/etc/httpd/modules/mod_ssl.so

[root@centos57 modssl]# ./build_modssl_with_npn.sh

Using buildroot: /tmp/tmp.CooHIy8770

Downloading http://www.openssl.org/source/openssl-1.0.1-beta2.tar.gz

######################################################################## 100.0%

Downloading http://www.apache.org/dist/httpd/httpd-2.2.21.tar.gz

######################################################################## 100.0%

Downloading https://issues.apache.org/bugzilla/attachment.cgi?id=27969context=patch

######################################################################## 100.0%

Uncompressing openssl-1.0.1-beta2.tar.gz ... done

Uncompressing httpd-2.2.21.tar.gz ... done

Applying Apache mod_ssl NPN patch ...

patching file modules/ssl/ssl_private.h

patching file modules/ssl/ssl_engine_init.c

patching file modules/ssl/ssl_engine_io.c

patching file modules/ssl/ssl_engine_kernel.c

patching file modules/ssl/mod_ssl.c

patching file modules/ssl/mod_ssl.h

done

Configuring OpenSSL ... done

Building OpenSSL (this may take a while) ... done

Configuring Apache mod_ssl ... done

Building Apache mod_ssl (this may take a while) ... done

Generated mod_ssl.so at /root/modssl/mod_ssl.so.

mod_spdy

• Built from source • mkdir mod_spdy; cd mod_spdy

• svn co http://src.chromium.org/svn/trunk/tools/depot_tools

• export PATH="$PATH":`pwd`/depot_tools

• gclient config http://mod-spdy.googlecode.com/svn/trunk/src

• gclient sync --force

• cd src; make BUILDTYPE=Release

• sudo cp out/Release/libmod_spdy.so /etc/httpd/modules/mod_spdy.so

• vi /etc/httpd/conf.d/spdy.conf

LoadModule spdy_module /etc/httpd/modules/mod_spdy.so

SpdyEnabled on

chrome://net-internals/#spdy

Is it spdy?

• www.devthought.com/2012/03/10/chrome-spdy-indicator/

• ckon.wordpress.com/2012/03/11/spdy-indicator-for-firefox/

HTTP

2.07 seconds

HTTPS

4.94 seconds

SPDY

2.65 seconds

real HTTP

17.83 seconds

real SPDY

11.70 seconds

LET'S MAKE THE WEB FASTER