The short but happy lives of TCP and HTTP requests

@StarrHorne Hi everybody!! ! I’ll be tweeting this ! slide
deck later at ! @StarrHorne ! ! That’s me!! ! ! ps. Use Honeybadger to monitor your Rails apps for exceptions. (Now my trip is tax deductible!)

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@StarrHorne Short but happy

@StarrHorne Short but happy The lives of HTTP requests

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@StarrHorne Welcome to the internet I’ll be your guide

@StarrHorne OSI Model

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@StarrHorne Wires

@StarrHorne Latency ! ! ! Time spent “in the wire”
! ps. it ain’t bandwidth

@StarrHorne Minimum latency (determined by speed of light) http://trollphysics.tumblr.com

@StarrHorne 299,792,458 m/s (Speed of light in a vacuum) http://trollphysics.tumblr.com

@StarrHorne Don’t call it SOL in a vacuum (That’s something
else) http://trollphysics.tumblr.com

@StarrHorne

@StarrHorne ! 5,578,593(m) ÷ 299,792,458 (m/s) = 0.0186 (s) !
0.0186 * 1000 (ms/s) = 18.6ms ! 18.6 * 2 = 37.2 ms round trip NYC <=> LON Latency (minimum theoretical)

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@StarrHorne Latency kills UX 100 ms Doesn’t seem instantaneous 250
ms Feels sluggish 500 ms I start to get distracted 1000 ms I’m cussing at the computer

@StarrHorne Easy Move servers closer to users.

@StarrHorne Harder Eliminate Round Trips

@StarrHorne The Data Link

@StarrHorne Bandwidth It must be important. Just look at that
dude’s face!

@StarrHorne Except when it’s not Source: High Performance Browser Networking
( http://bit.ly/high-performance-browser-networking )

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@StarrHorne The “lots of small ﬁles” problem Slower Faster

@StarrHorne Blame the protocols IP Routes packets between computers No
guarantees of delivery. TCP A simulation of a stable network running on top of IP. HTTP Sends one ﬁle at a time over TCP connections.

@StarrHorne ! NEW TCP CONNECTIONS ARE EXPENSIVE

@StarrHorne Opening a connection Hey, we should talk Sure, about
what? Awesome. Send me that funny cat pic

@StarrHorne New connection overhead (1 round trip. 20-100ms depending)

@StarrHorne ! YOU’RE NOT GETTING OFF THAT EASY

@StarrHorne CONGESTION CONTROL

@StarrHorne Slow Start

@StarrHorne Let’s see… Thats 10 round trips at (we’ll assume)
40ms latency. Holy crap that’s 400ms!!!

@StarrHorne ! NEW TCP CONNECTIONS ARE EXPENSIVE

@StarrHorne Keep-Alive Browser opens one TCP connection uses it for
multiple HTTP requests. ! ! ! ! ! ! ! …actually, you get 6 connections per domain.

@StarrHorne Your server controls keepalive ! ! Apache: http://bit.ly/apache-ka !
Nginx: http://bit.ly/nginx-ka !

@StarrHorne “Slow start after idle” kills keepalive ! $> sysctl
net.ipv4.tcp_slow_start_after_idle ! $> sysctl -w net.ipv4.tcp_slow_start_after_idle=0

@StarrHorne TCP Tuning Make sure you’re running a recent linux
kernel If you insist: http://bit.ly/tcp-tuning

@StarrHorne HTTP, WTF!?

@StarrHorne >telnet cern.ch 80 GET /cat.txt HTTP/1.0 host: www.esqsoft.globalservers.com

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@StarrHorne 112 (Requests per webpage on average)

@StarrHorne Browser Caching (Response headers) Last-Modified Tell the browser when
this file was last modified. ETag Supplies an ETag the browser can use to check freshness. Expires Tells the browser to keep the page until a certain date http://bit.ly/http-caching

@StarrHorne 112 (Requests per webpage on average)

@StarrHorne Concatenate JS & CSS (Hello asset pipeline)

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Down to 30 requests (But I feel dirty for some
reason) @StarrHorne

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@StarrHorne Could we do them CONCURRENTLY? ! ! ! !
! You DO get 6 connections per domain. And you DO know how to make domains.

@StarrHorne farm4.staticflickr.com farm8.staticflickr.com farm8.staticflickr.com farm4.staticflickr.com farm6.staticflickr.com farm3.staticflickr.com http://bit.ly/p-speed

@StarrHorne I guess you could call it an ugly hack

@StarrHorne www.honeybadger.io d3aei7d2k8qp8j.cloudfront.net cdnjs.cloudﬂare.com d3dy5gmtp8yhk7.cloudfront.net cdnjs.cloudﬂare.com But we do it
anyway (As a side-effect of using CDNs)

@StarrHorne Move requests out of band (Supported by newer browsers)
! <script async="async" src="/my.js"></script> ! <link rel="prefetch" href=“/big.jpeg"> ! <link rel="prerender" href=“/next.html”> ! <link rel="dns-prefetch" href="//blah.com">

@StarrHorne Summary ! Move your servers closer to your users
(CDNs) ! Make sure keep-alive works ! Keep cookie size small ! Serve fewer ﬁles by whatever means necessary ! Shard ﬁles across domains if you must !

@StarrHorne The cavalry is on the way!

@StarrHorne SPDY ! Much better at the “lots of small
ﬁles” thing ! Supported by many (but not all) clients ! You still need CDNs for geography ! Requires SSL

@StarrHorne HTTP 2.0 ! Coming soon. ! Also focused on
the “lots of small ﬁles” problem ! But HTTP 1.4 ain’t going anywhere soon.

@StarrHorne Buy this book ! You can also read it
online for free - legally! ! http://bit.ly/high-performance-browser-networking

@StarrHorne I’ll be tweeting this slide deck later at @StarrHorne

The short but happy lives of TCP and HTTP requests

The short but happy lives of TCP and HTTP requests

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