Taming the Unicorn

The Unicorn web server is a workhorse in the Ruby world. It's used by major Rails sites like Shopify, Github, and 37Signals.

Learn about some of the core features of Unicorn and what makes it special. This'll start at the start and take you through system calls, (pre)forking, signals, kgio, and tricks to conserve memory.

Transcript

1. Taming the Unicorn Demystify your Unix system jesse@shopify.com @jstorimer jstorimer.com workingwithunixprocesses.com 1
3. Find me at http://unicorn.bogomips.org 3
5. You have to know what’s possible 5
6. Join the Lineage 6
7. “Thirty years from now, there will still be [system calls] and smart people will still be using them to solve hard problems reliably and predictably, just like they were thirty years ago.” ~ Ryan Tomayko 7
8. It’s all about system calls 8
9. Documentation Code 9
10. Documentation •intro(2) -> $ man 2 intro Code 9
11. Documentation •intro(2) -> $ man 2 intro •malloc(3) -> $ man 3 malloc Code 9
12. Documentation •intro(2) -> $ man 2 intro •malloc(3) -> $ man 3 malloc •crontab(5) -> $ man 5 crontab Code 9
13. Documentation •intro(2) -> $ man 2 intro •malloc(3) -> $ man 3 malloc •crontab(5) -> $ man 5 crontab •[Linux only] socket(7) -> $ man 7 socket Code 9
14. Documentation •intro(2) -> $ man 2 intro •malloc(3) -> $ man 3 malloc •crontab(5) -> $ man 5 crontab •[Linux only] socket(7) -> $ man 7 socket •$ apropos thing; Searches the manpages Code 9
15. UNIX POSIX Linux FreeBSD Darwin you-nix? Pick ‘the’ Unix 10
18. Preforking 12
19. Preforking Signal handling 12
20. Preforking Signal handling kgio 12
21. Preforking Signal handling kgio Bets and Memory Tricks 12
22. Preforking Signal handling kgio Bets and Memory Tricks Zero downtime restarts? 12
23. Preforking Signal handling kgio Bets and Memory Tricks Zero downtime restarts? Code spelunking? 12
24. Preforking 1.First, Forking 2.Then, Pre 13
25. fork(2) system call Code 14
26. Processes are the fundamental units 15
27. fork(2) creates an *exact* copy of the current process 16
32. Parent and child execute independently Parent can exit and child lives on Code 21
33. Now to add the pre Code 22
34. require 'socket' concurrency = 3 child_pids = [] signal_queue = [] socket = TCPServer.open('127.0.0.1', 4481) concurrency.times do child_pids << fork do trap(:INT) { exit } loop do connection = socket.accept connection.write(connection.read) connection.close end end end [:INT, :CHLD].each do |sig| trap(sig) do signal_queue << sig end end 23
35. require 'socket' concurrency = 3 child_pids = [] signal_queue = [] socket = TCPServer.open('127.0.0.1', 4481) concurrency.times do child_pids << fork do trap(:INT) { exit } loop do connection = socket.accept connection.write(connection.read) connection.close end end end [:INT, :CHLD].each do |sig| trap(sig) do signal_queue << sig end end Parent Process Child Processes 24
36. Further Reading •fork(2) •wait(2) •https://github.com/defunkt/unicorn/ blob/master/lib/unicorn/ http_server.rb#L483-494 25
37. Signal Handling 26
38. Sending a signal •kill(1) or Process.kill •Each signal can be represented with a name or number •Anyone ever use? $kill -9 <pid> Code 27
39. Caveats of signal handling •Handlers may run at *any* time •Your handlers must be re-entrant Code 28
40. Further Reading •Unicorn’s signal queue: https:// github.com/defunkt/unicorn/blob/ master/lib/unicorn/ http_server.rb#L262 •https://github.com/defunkt/unicorn/ blob/master/lib/unicorn/ http_server.rb#L131 •signal(7) 29
41. kgio Kindler, gentler, IO for ruby. 30
42. Why? Code 31
43. Why? •Unicorn uses nonblocking IO methods Code 31
44. Why? •Unicorn uses nonblocking IO methods •They raise Errno::EAGAIN when they would block Code 31
45. Why? •Unicorn uses nonblocking IO methods •They raise Errno::EAGAIN when they would block •Socket#accept will block until it gets a connection Code 31
46. Why? •Unicorn uses nonblocking IO methods •They raise Errno::EAGAIN when they would block •Socket#accept will block until it gets a connection •Socket#accept_nonblock will get a connection or raise Errno::EAGAIN Code 31
47. Why? Code 32
48. Why? Exceptions in Ruby (and other langs) are expensive Code 32
49. Bets and Memory Tricks But first, a note on micro-optimization 33
50. (A made-up definition) mi·cro·op·ti·mi·za·tion n. 1. Making the code more efficient by making it more obscure. 34
51. Don’t Micro-optimize Applications 35
52. It’s about tradeoffs •Would you rather get another 1 ms of performance or get Feature X implemented? •Applications set their own standards 36
53. System software has to micro-optimize •It’s at the mercy of the standards of the application •What if an application wants really fast responses and the server holds them back? 37
54. Let’s pretend for a minute What if Unicorn could save 0.1ms per request? 38
55. # make the following bet: if we accepted clients this round, # we're probably reasonably busy, so avoid calling select() # and do a speculative non-blocking accept() on ready listeners # before we sleep again in select(). unless nr == 0 # (nr < 0) => reopen logs (unlikely) ready = l.dup redo end 39
56. ... # A frozen format for this is about 15% faster REMOTE_ADDR = 'REMOTE_ADDR'.freeze ... e[REMOTE_ADDR] = socket.kgio_addr ... # This is the typical way to accomplish the above: e['REMOTE_ADDR'] = socket.kgio_addr 40
57. # Does the majority of the IO processing. It has been written in # Ruby using about 8 different IO processing strategies. # # It is currently carefully constructed to make sure that it gets # the best possible performance for the common case: GET requests # that are fully complete after a single read(2) # # Anyone who thinks they can make it faster is more than welcome to # take a crack at it. # # returns an environment hash suitable for Rack if successful # This does minimal exception trapping and it is up to the caller # to handle any socket errors (e.g. user aborted upload). def read(socket) 41
58. Go read my source code! http://unicorn.bogomips.org/ 42
60. Resources •Unicorn source code (http:// unicorn.bogomips.org/) •usp.ruby list (http://librelist.com/browser/ usp.ruby/) •http://tomayko.com/writings/unicorn-is-unix •https://github.com/blog/517-unicorn2010/ everything-you-need-to-know-about-unicorn/ •http://www.engineyard.com/blog/2010/ everything-you-need-to-know-about-unicorn/ 44
61. Credits • Unicorn 502 page: http://chuckjhardy.com/post/3329075019/github-502-unicorn-server- error • The thinker: http://www.flickr.com/photos/22087304@N07/5074344673/ • Ritchie and Thompson: http://catb.org/~esr/writings/taoup/html/ch02s01.html • Blocks: http://www.flickr.com/photos/kmtucker/3355551036/ • Signal: http://www.flickr.com/photos/philipstorry/4924064517/ • Color scheme: http://www.colourlovers.com/palette/1111659/Ninja_Rainbow 45