Doing horrible things to DNS involves using CNAME records to create multiple domain names that resolve to the same IP addresses. This allows making a single DNS query but receiving responses for multiple domains, enabling more parallel HTTP requests. The technique involves creating a chain of CNAME records that ultimately resolve to a single canonical name, gaining the ability to load resources from different apparent hostnames while only requiring one DNS lookup.

1. Doing
Horrible Things
to DNS
(in the name of science)
@sh1mmer Yahoo! Inc

2. The basics of DNS

10. San Francisco - Mission Branch

13. San Francisco - Main Library

16. New York City - 5th & 42nd Branch

19. New York City - 5th & 42nd Branch

21. NYC
San Francisco - Main Library

22. San Francisco - Main Library

24. NYC
SF
San Francisco - Mission Branch

25. San Francisco - Mission Branch

27. NYC
SF
Mission

29. NYC
SF
Mission
Me

31. GTFO!
It's 3am!

32. DNS for performance

33. Page Load Time vs. Bandwidth

34. Page Load Time vs. Round Trip Time

35. Trend Curves for Bandwidth vs. RTT

36. Serial HTTP loading - 1 domain

37. Parallel HTTP loading - 3 domains

38. So why not just use a loads of domains?

39. DNS Lookup

40. Ideal? 1 DNS query many parallel threads

41. Option 1: SPDY (by Google)

42. Good: Multi-thread TCP connections
Bad: Only works on Chrome :(

43. Option 2: Do horrible things to DNS

44. Mucking about with C names

45. CNAMES are hosts which
are aliases of other hosts

46. enki:~ $ dig yahoo.com
; <<>> DiG 9.4.3-P3 <<>> yahoo.com
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 32801
;; flags: qr rd ra; QUERY: 1, ANSWER: 5, AUTHORITY: 7, ADDITIONAL: 7
;; QUESTION SECTION:
;yahoo.com. IN A Query
;; ANSWER SECTION:
yahoo.com. 5935 IN A 69.147.125.65
yahoo.com. 5935 IN A 72.30.2.43
yahoo.com. 5935 IN A 98.137.149.56
yahoo.com.
yahoo.com.
5935
5935
IN
IN
A
A
209.191.122.70
67.195.160.76 Response
...
;; Query time: 45 msec
;; SERVER: 202.171.190.10#53(202.171.190.10)
;; WHEN: Wed Oct 13 17:23:39 2010
;; MSG SIZE rcvd: 345

47. ajax1.hackerhouse.org. 1800 IN CNAME ajax2.hackerhouse.
ajax2.hackerhouse.org. 1800 IN CNAME ajax3.hackerhouse.
ajax3.hackerhouse.org. 1800 IN CNAME ajax4.hackerhouse.
ajax4.hackerhouse.org. 1800 IN CNAME ajax.hackerhouse.
ajax.hackerhouse.org. 1800 IN A 192.168.1.1
ajax.hackerhouse.org. 1800 IN A 192.168.1.2
ajax.hackerhouse.org. 1800 IN A 192.168.1.3
ajax.hackerhouse.org. 1800 IN A 192.168.1.4
ajax.hackerhouse.org. 1800 IN A 192.168.1.5

48. We now have 5 hostnames with 1 DNS query

49. 5 hostnames x 6 request per host
=
30 parallel requests

50. Doing
Horrible Things
to DNS
(in the name of science)
Questions?
@sh1mmer Yahoo! Inc