HTTP for Great Good

Scaling Django with HTTP

DjangoCon US 2013

http://www.youtube.com/watch?v=HAjOQ09I1UY

Transcript

1. HTTP for Great Good Scaling Django with HTTP DjangoCon US September 5th 2013 Matt Robenolt
2. Hello < me irl
3. Site Reliability Engineer
4. “DJANGO ALL THE THINGS!”
5. “...but
6. “...but
7. The slowest part of a web application is typically not your code.
8. Between databases and memcaches and Redises and Cassandras and MongoDBs and networks, Django is not the problem.
9. “...everything
11. A few vanity metrics.
12. Monthly Unique Visitors 1,115,080,411
13. Monthly Page Views 7,516,761,301
14. Inbound Traffic 42k total req/s 15k app req/s not my fault
15. 36% of all requests actually hit a Django server 15k/42k = 36%
16. ...what happened to the other 64%?
17. Let’s talk about HTTP. Hypertext Transport Protocol
18. $ curl -v disqus.com
19. > GET / HTTP/1.1 > User-Agent: curl/7.24.0 > Host: disqus.com > Accept: */* > < HTTP/1.1 200 OK < Server: nginx < Date: Fri, 30 Aug 2013 06:38:37 GMT < Content-Type: text/html; charset=utf-8 < Content-Length: 10453 < Last-Modified: Fri, 30 Aug 2013 00:32:14 GMT < Vary: Accept-Encoding < Expires: Fri, 30 Aug 2013 06:38:36 GMT < Cache-Control: no-cache, must-revalidate
20. > GET / HTTP/1.1 > User-Agent: curl/7.24.0 > Host: disqus.com > Accept: */* > < HTTP/1.1 200 OK < Server: nginx < Date: Fri, 30 Aug 2013 06:38:37 GMT < Content-Type: text/html; charset=utf-8 < Content-Length: 10453 < Last-Modified: Fri, 30 Aug 2013 00:32:14 GMT < Vary: Accept-Encoding < Expires: Fri, 30 Aug 2013 06:38:36 GMT < Cache-Control: no-cache, must-revalidate Request
21. > GET / HTTP/1.1 > User-Agent: curl/7.24.0 > Host: disqus.com > Accept: */* > < HTTP/1.1 200 OK < Server: nginx < Date: Fri, 30 Aug 2013 06:38:37 GMT < Content-Type: text/html; charset=utf-8 < Content-Length: 10453 < Last-Modified: Fri, 30 Aug 2013 00:32:14 GMT < Vary: Accept-Encoding < Expires: Fri, 30 Aug 2013 06:38:36 GMT < Cache-Control: no-cache, must-revalidate Method
22. > GET / HTTP/1.1 > User-Agent: curl/7.24.0 > Host: disqus.com > Accept: */* > < HTTP/1.1 200 OK < Server: nginx < Date: Fri, 30 Aug 2013 06:38:37 GMT < Content-Type: text/html; charset=utf-8 < Content-Length: 10453 < Last-Modified: Fri, 30 Aug 2013 00:32:14 GMT < Vary: Accept-Encoding < Expires: Fri, 30 Aug 2013 06:38:36 GMT < Cache-Control: no-cache, must-revalidate Path
23. > GET / HTTP/1.1 > User-Agent: curl/7.24.0 > Host: disqus.com > Accept: */* > < HTTP/1.1 200 OK < Server: nginx < Date: Fri, 30 Aug 2013 06:38:37 GMT < Content-Type: text/html; charset=utf-8 < Content-Length: 10453 < Last-Modified: Fri, 30 Aug 2013 00:32:14 GMT < Vary: Accept-Encoding < Expires: Fri, 30 Aug 2013 06:38:36 GMT < Cache-Control: no-cache, must-revalidate Version
24. > GET / HTTP/1.1 > User-Agent: curl/7.24.0 > Host: disqus.com > Accept: */* > < HTTP/1.1 200 OK < Server: nginx < Date: Fri, 30 Aug 2013 06:38:37 GMT < Content-Type: text/html; charset=utf-8 < Content-Length: 10453 < Last-Modified: Fri, 30 Aug 2013 00:32:14 GMT < Vary: Accept-Encoding < Expires: Fri, 30 Aug 2013 06:38:36 GMT < Cache-Control: no-cache, must-revalidate Headers
25. > GET / HTTP/1.1 > User-Agent: curl/7.24.0 > Host: disqus.com > Accept: */* > < HTTP/1.1 200 OK < Server: nginx < Date: Fri, 30 Aug 2013 06:38:37 GMT < Content-Type: text/html; charset=utf-8 < Content-Length: 10453 < Last-Modified: Fri, 30 Aug 2013 00:32:14 GMT < Vary: Accept-Encoding < Expires: Fri, 30 Aug 2013 06:38:36 GMT < Cache-Control: no-cache, must-revalidate Response
26. > GET / HTTP/1.1 > User-Agent: curl/7.24.0 > Host: disqus.com > Accept: */* > < HTTP/1.1 200 OK < Server: nginx < Date: Fri, 30 Aug 2013 06:38:37 GMT < Content-Type: text/html; charset=utf-8 < Content-Length: 10453 < Last-Modified: Fri, 30 Aug 2013 00:32:14 GMT < Vary: Accept-Encoding < Expires: Fri, 30 Aug 2013 06:38:36 GMT < Cache-Control: no-cache, must-revalidate Status
27. > GET / HTTP/1.1 > User-Agent: curl/7.24.0 > Host: disqus.com > Accept: */* > < HTTP/1.1 200 OK < Server: nginx < Date: Fri, 30 Aug 2013 06:38:37 GMT < Content-Type: text/html; charset=utf-8 < Content-Length: 10453 < Last-Modified: Fri, 30 Aug 2013 00:32:14 GMT < Vary: Accept-Encoding < Expires: Fri, 30 Aug 2013 06:38:36 GMT < Cache-Control: no-cache, must-revalidate Headers
28. Request in Django request.method # method request.get_full_path() # path request.META['HTTP_USER_AGENT'] request.META['HTTP_ACCEPT']
29. Response in Django response = HttpResponse(body) response.status_code = 200 response['X-Foo'] = 'bar'
30. “Cool,
31. > GET / HTTP/1.1 > User-Agent: curl/7.24.0 > Host: disqus.com > Accept: */* > < HTTP/1.1 200 OK < Server: nginx < Date: Fri, 30 Aug 2013 06:38:37 GMT < Content-Type: text/html; charset=utf-8 < Content-Length: 10453 < Last-Modified: Fri, 30 Aug 2013 00:32:14 GMT < Vary: Accept-Encoding < Expires: Fri, 30 Aug 2013 06:38:36 GMT < Cache-Control: no-cache, must-revalidate Hmm. What can we do with this information?
32. > GET / HTTP/1.1 > User-Agent: curl/7.24.0 > Host: disqus.com > Accept: */* > If-Modified-Since: Fri, 30 Aug 2013 00:32:14 GMT > < HTTP/1.1 304 Not Modified < Server: nginx < Date: Fri, 30 Aug 2013 18:05:38 GMT < Last-Modified: Fri, 30 Aug 2013 00:32:14 GMT < Vary: Accept-Encoding < Expires: Fri, 30 Aug 2013 18:05:37 GMT < Cache-Control: no-cache, must-revalidate
33. 304 Not Modified No body is sent with the response
34. 304 Not Modified Client reuses its cached version
35. 304 Not Modified Usually more efficient to calculate
36. notbad.gif
37. But we can do better!
38. Static files have been promoting good practices for a long time.
39. “Far future headers”
40. $ curl -v a.disquscdn.com/dotcom/d-6203c8f/css/ disqus-web/pages/home.css < HTTP/1.1 200 OK < Server: nginx < Content-Type: text/css; charset=utf-8 < Last-Modified: Fri, 16 Aug 2013 20:31:05 GMT < Expires: Sun, 15 Sep 2013 20:34:21 GMT < Cache-Control: max-age=2592000 < Content-Length: 30749 < Date: Sun, 18 Aug 2013 03:23:37 GMT < Via: 1.1 varnish < Age: 110956 < Connection: keep-alive < Vary: Accept-Encoding
41. $ curl -v a.disquscdn.com/dotcom/d-6203c8f/css/ disqus-web/pages/home.css < HTTP/1.1 200 OK < Server: nginx < Content-Type: text/css; charset=utf-8 < Last-Modified: Fri, 16 Aug 2013 20:31:05 GMT < Expires: Sun, 15 Sep 2013 20:34:21 GMT < Cache-Control: max-age=2592000 < Content-Length: 30749 < Date: Sun, 18 Aug 2013 03:23:37 GMT < Via: 1.1 varnish < Age: 110956 < Connection: keep-alive < Vary: Accept-Encoding 30 days in the future.
42. Chrome Web Inspector on second visit
43. No HTTP request 0ms
44. No HTTP request The client knew to just use its local cache
45. No HTTP request Computer actually did something right for once
46. “I SEE WHAT YOU DID THERE” - Hopefully you
47. Takeaways Clients behave differently depending on the response headers
48. Takeaways These usually come with minimal effort with static files
49. Takeaways We can and should utilize these to our advantage to improve UX
50. Same logic can be applied to dynamic content.
51. What’s this look like in Django?
52. Last-Modified def lol(request): response = render(request, 'lol.html') response['Last-Modified'] = \ 'Fri, 16 Aug 2013 20:31:05 GMT' return response * don’t do this.
53. Last-Modified from django.views.decorators.http import \ last_modified def post_last_modified(request, slug): return Post.objects.get(slug=slug).modified @last_modified(post_last_modified) def blog_post_detail(request, slug): # Your view
54. Cache-Control def lol(request): response = render(request, 'lol.html') response['Cache-Control'] = 'max-age=600' return response
55. Cache-Control from django.views.decorators.cache import \ cache_control @cache_control(max_age=600) # Cache for 10m def home(request): return HttpResponse('lol')
56. “OMG!
58. Well... not really.
59. How many requests will {{user}} make to the same page within 10 minutes?
60. 1? 2? 3?
61. ...out of 42k requests per second.
62. Even with caching, your app is doing a lot of work.
63. Parsing HTTP.
64. WSGI.
65. Django middleware stack.
66. Do some stuff.
67. Render a template?
68. Back out through the Django middleware.
69. Transform an HttpResponse into a real HTTP response.
70. ...at 42k requests per second.
71. You’re gonna have a bad time. me
72. Until now, “client” has been a user’s browser.
73. “If only we could utilize this Cache-Control stuff better...”
74. Introducing
75. $ apt-get install varnish
76. $ brew install varnish
77. tl;dr Varnish sits between Django and your users Internet
78. tl;dr Caches HTTP responses and respects proper HTTP headers Internet
79. tl;dr Its sole purpose in life is to be a cache, so it’s really fast. Internet
80. Stand back, science is happening.
81. Stand back, science is happening. benchmarking
82. Simple, non-scientific “Hello World”
83. from django.views.decorators.cache import \ cache_control from django.http import HttpResponse @cache_control(max_age=5) def hello(request): return HttpResponse('Hello world') “Hello World”
84. $ httperf --server 127.0.0.1 --port 8000 -- uri /hello/ --rate 150 --num-conn 10 --num-call 500 --hog Request rate: 369.6 req/s (2.7 ms/req) Django + gunicorn * on my MacBook Air
85. $ httperf --server 127.0.0.1 --port 8888 -- uri /hello/ --rate 150 --num-conn 10 --num-call 10000 --hog Request rate: 15633.4 req/s (0.1 ms/req) Varnish * on my MacBook Air
86. Varnish: How does it work?
87. First request
88. First response “Lemme
89. “Yo,
90. Next response “wut
91. Caching: ProMoves™
92. Augment with JavaScript Update your UI optimistically
93. Augment with JavaScript Leverage cookies to store non-critical data
94. Augment with JavaScript Defer fetching user-specific data until needed
95. Short TTLs are good Most things can be cached for at least 5s
96. Short TTLs are good At 10k requests/s, a 5s TTL absorbs 49,999 requests
97. Let’s meet: John and Jane Doe.
98. John and Jane are different users.
99. John logs into Disqus.
100. Jane logs into Disqus.
101. Jane sees John’s stuff.
102. Jane sees John’s stuff. ^ not
103. We really want to avoid this from ever happening.
104. Cookies
105. How do users even work?
106. $ curl -vd "username=foo&password=bar" https:// disqus.com/profile/login/ > POST /profile/login/ HTTP/1.1 > User-Agent: curl/7.24.0 > Host: disqus.com > < HTTP/1.1 302 FOUND < Server: nginx < Date: Fri, 30 Aug 2013 21:34:36 GMT < Vary: Cookie < Set-Cookie: sessionid=f7aa9598-11bb-11e3-9eb1-003048d9a288; Domain=.disqus.com; expires=Sun, 29-Sep-2013 21:34:36 GMT; httponly; Max-Age=2592000; Path=/
107. $ curl -vd "username=foo&password=bar" https:// disqus.com/profile/login/ > POST /profile/login/ HTTP/1.1 > User-Agent: curl/7.24.0 > Host: disqus.com > < HTTP/1.1 302 FOUND < Server: nginx < Date: Fri, 30 Aug 2013 21:34:36 GMT < Vary: Cookie < Set-Cookie: sessionid=f7aa9598-11bb-11e3-9eb1-003048d9a288; Domain=.disqus.com; expires=Sun, 29-Sep-2013 21:34:36 GMT; httponly; Max-Age=2592000; Path=/ Set-Cookie
108. $ curl -vd "username=foo&password=bar" https:// disqus.com/profile/login/ > POST /profile/login/ HTTP/1.1 > User-Agent: curl/7.24.0 > Host: disqus.com > < HTTP/1.1 302 FOUND < Server: nginx < Date: Fri, 30 Aug 2013 21:34:36 GMT < Vary: Cookie < Set-Cookie: sessionid=f7aa9598-11bb-11e3-9eb1-003048d9a288; Domain=.disqus.com; expires=Sun, 29-Sep-2013 21:34:36 GMT; httponly; Max-Age=2592000; Path=/ Session Id
109. Unique id that represents a logged in user Session Id
110. django.contrib.sessions / django.contrib.auth Session Id
111. Could potentially cache per session id Session Id
112. By default, Varnish will not cache any request with a Cookie header at all.
113. Think about if your endpoint changes based on a user’s authentication.
114. If it doesn’t, Varnish can normalize it.
116. Learn: Varnish Configuration Language (VCL) in 30 seconds
117. sub vcl_recv { // These urls can be stripped of all // cookies since they serve the same // data for anon and auth'd user if ( req.url == "/" || req.url ~ "^/embed/comments/" ) { unset req.http.Cookie; } }
118. Basically, caching is hard.
119. Go make some stuff faster.
120. We’re hiring people who hate computers. disqus.com/jobs
121. Questions? I have answers. ^ github.com/mattrobenolt @mattrobenolt some