The short but happy lives of TCP and HTTP requests

A talk about network optimization given at the 2014 Golden Gate Ruby Conference.

Transcript

1. @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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4. @StarrHorne Short but happy
5. @StarrHorne Short but happy The lives of HTTP requests
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13. @StarrHorne Welcome to the internet I’ll be your guide
14. @StarrHorne OSI Model
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19. @StarrHorne Wires
20. @StarrHorne Latency ! ! ! Time spent “in the wire” ! ps. it ain’t bandwidth
21. @StarrHorne Latency ! ! ! Time spent “in the wire” ! ps. it ain’t bandwidth
22. @StarrHorne Minimum latency (determined by speed of light) http://trollphysics.tumblr.com
23. @StarrHorne Minimum latency (determined by speed of light) http://trollphysics.tumblr.com
24. @StarrHorne 299,792,458 m/s (Speed of light in a vacuum) http://trollphysics.tumblr.com
25. @StarrHorne Don’t call it SOL in a vacuum (That’s something else) http://trollphysics.tumblr.com
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27. @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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29. @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
30. @StarrHorne Easy Move servers closer to users.
31. @StarrHorne Harder Eliminate Round Trips
32. @StarrHorne The Data Link
33. @StarrHorne Bandwidth It must be important. Just look at that dude’s face!
34. @StarrHorne Except when it’s not Source: High Performance Browser Networking ( http://bit.ly/high-performance-browser-networking )
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36. @StarrHorne The “lots of small files” problem Slower Faster
37. @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.
38. @StarrHorne ! NEW TCP CONNECTIONS ARE EXPENSIVE
39. @StarrHorne Opening a connection Hey, we should talk Sure, about what? Awesome. Send me that funny cat pic
40. @StarrHorne New connection overhead (1 round trip. 20-100ms depending)
41. @StarrHorne ! YOU’RE NOT GETTING OFF THAT EASY
42. @StarrHorne CONGESTION CONTROL
43. @StarrHorne Slow Start
44. @StarrHorne Let’s see… Thats 10 round trips at (we’ll assume) 40ms latency. Holy crap that’s 400ms!!!
45. @StarrHorne ! NEW TCP CONNECTIONS ARE EXPENSIVE
46. @StarrHorne Keep-Alive Browser opens one TCP connection uses it for multiple HTTP requests. ! ! ! ! ! ! ! …actually, you get 6 connections per domain.
47. @StarrHorne Your server controls keepalive ! ! Apache: http://bit.ly/apache-ka ! Nginx: http://bit.ly/nginx-ka !
48. @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
49. @StarrHorne TCP Tuning Make sure you’re running a recent linux kernel If you insist: http://bit.ly/tcp-tuning
50. @StarrHorne HTTP, WTF!?
51. @StarrHorne >telnet cern.ch 80 GET /cat.txt HTTP/1.0 host: www.esqsoft.globalservers.com
52. @StarrHorne >telnet cern.ch 80 GET /cat.txt HTTP/1.0 host: www.esqsoft.globalservers.com
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56. @StarrHorne 112 (Requests per webpage on average)
57. @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
58. @StarrHorne 112 (Requests per webpage on average)
59. @StarrHorne Concatenate JS & CSS (Hello asset pipeline)
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62. Down to 30 requests (But I feel dirty for some reason) @StarrHorne
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64. @StarrHorne Could we do them CONCURRENTLY? ! ! ! ! ! You DO get 6 connections per domain. And you DO know how to make domains.
65. @StarrHorne farm4.staticflickr.com farm8.staticflickr.com farm8.staticflickr.com farm4.staticflickr.com farm6.staticflickr.com farm3.staticflickr.com http://bit.ly/p-speed
66. @StarrHorne I guess you could call it an ugly hack
67. @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)
68. @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">
69. @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 !
70. @StarrHorne The cavalry is on the way!
71. @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
72. @StarrHorne HTTP 2.0 ! Coming soon. ! Also focused on the “lots of small files” problem ! But HTTP 1.4 ain’t going anywhere soon.
73. @StarrHorne Buy this book ! You can also read it online for free - legally! ! http://bit.ly/high-performance-browser-networking
74. @StarrHorne I’ll be tweeting this slide deck later at @StarrHorne