Talk given at the Gilt Groupe Experts Talk in NYC, December 2009.

1. Hello.
Hi everyone.

2. My name is Chris Wanstrath. I go by @defunkt online.

3. inside
github
And today I’m going to talk about GitHub.

4. inside
github
That’s me.

5. GitHub is what we like to call “social coding.”

6. You can see what your friends are doing from your dashboard or news feed

7. Everyone has a profile showing off their code and activity

8. And you can do things like leave comments on commits.

9. But it wasn’t always like this.

10. Originally we just wanted to make a git hosting site.
In fact, that was the first tagline.

11. git repository hosting
git repository hosting.
That’s what we wanted to do: give us and our friends a place to share git repositories.

12. It’s not easy to setup a git repository. It never was.
But back in 2007 I really wanted to.

13. I had seen Torvalds’ talk on YouTube about git.
But it wasn’t really about git - it was more about distributed version control.
It answered many of my questions and clarified DVCS ideas.
I still wasn’t sold on the whole idea, and I had no idea what it was good for.

14. CVS
is stupid
But when Torvalds says “CVS is stupid”

15. and so are
you
“and so are you,” the natural reaction for me is...

16. To start learning git.

17. At the time the biggest and best free hosting site was repo.or.cz.

18. Right after I had seen the Torvalds video, the god project was posted up on repo.or.cz
I was interested in the project so I finally got a chance to try it out with some other people.

19. Namely this guy, Tom Preston-Werner.
Seen here in his famous “I put ketchup on my ketchup” shirt.

20. I managed to make a few contributions to god before realizing that repo.or.cz was not different.
git was not different.
Just more of the same - centralized, inflexible code hosting.

21. This is what I always imagined.
No rules. Project belongs to you, not the site. Share, fork, change - do what you want.
Give people tools and get out of their way. Less ceremony.

22. So, we set off to create our own site.
A git hub - learning, code hosting, etc.

23. We started with the code browsing and commit viewing...

24. But once we added the current version of the dashboard, we knew this was different.

25. And eventually “git repository hosting” gave way to “social coding”

26. What’s special about GitHub is that people use the site in spite of git.
Many git haters use the site because of what it is - more than a place to host
git repositories, but a place to share code with others.

27. a brief
history
So that’s how it all started.
Now I want to (briefly) cover some milestones and events.

28. 2007 october
The first commit was on a Friday night in October, around 10pm.

29. 2008 january
We launched the beta in January at Steff’s on 2nd street in San Francisco’s SOMA district.
The first non-github user was wycats, and the first project was merb-core.
They wanted to use the site for their refactoring and 0.9 branch.

30. 2008 april
A few short months after that we launched to the public.

31. 2009 january
In January of this year, we were awared the “Best Bootstrapped Startup”
by TechCrunch.

32. 2009 april
Then in April we were featured as some of the best young tech entrepreneurs
in BusinessWeek.
(Finally something to show mom)

33. 2009 june
Our Firewall Install, something we’d been talking about since practically
day one, was launched in June of 2009.

34. 2009 september
And in September we moved to Rackspace, our current hosting provider.
(Which some of you may have noticed.)

35. Along the way we managed to pick up Scott Chacon, our VP of R&D

36. Tekkub, our level 80 support druid

37. Melissa Severini, who keeps us all in check

38. Kyle Neath, who makes the site pretty

39. And Ryan Tomayko, who helps keep the site running smoothly.

40. Oh yeah, and the other founders: PJ and Tom.

41. github.com
That’s where we’re at today.
So let’s talk about the technical details of the website: github.com

42. .com as opposed to fi, which I’m not going to get into today.
You’ll have to invite PJ out if you want to hear about that.

43. the
web app
As everyone knows, a web “site” is really a bunch of different components.
Some of them generate and deliver HTML to you, but most of them don’t.
Either way, let’s start with the HTMLy parts.

44. rails
We use Ruby on Rails 2.2.2 as our web framework.
It’s kept up to date with all the security patches and includes custom patches we’ve added
ourselves, as well as patches we’ve cherry-picked from more recent versions of Rails.

45. We found out Rails was moving to GitHub in March 2008, after we had reached out to
them and they had turned us down.
So it was a bit of a surprise.

46. rails
But there are entire presentations on Rails, so I’m not going to get further
into it here.
As for whether it scales or not, we’ll let you know when we find out. Because so far
it hasn’t come close to presenting a problem.

47. rack
One of the big features in Rails 2.3 is Rack support.

48. We badly wanted this, but didn’t want to invest the time upgrading.
So using a few open source libraries we’ve wrapped our Rails 2.2.2 instance in Rack.

49. Now we can use awesome Rack middleware like Rack::Bug in GitHub

50. In fact, the Coderack competition is about to open voting to the public this week.
Coders created and submitted dozens of Rack middleware for the competition.
I was a judge so I got the see the submissions already. Some of my favorite
were

51. nerdEd / rack-validate

52. webficient / rack-tidy

53. talison / rack-mobile-detect
sets the X_MOBILE_DEVICE header to the mobile device, if
recognized

54. unicorn
We use unicorn as our application server
- master / worker
- 16 workers
- preforking

55. unicorn
- instant restart after kill
- hard 30s request timeouts
- control ram growth

56. unicorn
- 0 downtime deploys
- protects against bad rails startup
- migrations handled old fashioned way

57. nginx
For serving static content and slow clients, we use nginx
nginx is pretty much the greatest http server ever
it’s simple, fast, and has a great module system

58. nginx
Limit Zone
Limit simultaneous connections from a client

59. nginx
Limit Requests
Limit frequency of connections from a client
Anti-DDOS

60. nginx
I see many people using Rack to do what the Limit modules do.
Don’t.

61. nginx
memcached
memcached support
can serve directly from memcached

62. nginx
Push Module
comet!

63. git
The next major part of GitHub is git

64. grit
We wrote an open source library called Grit
which lets us use git from Ruby

65. mojombo / grit
you can get it here
it originally shelled out to git and just parsed the responses.
which worked well for a long time.

66. grit
File.read()
Eventually we realized, however, that File.read() can be 100 times faster

67. grit
system()
Than shelling out

68. One of the first things Scott worked on was rewriting the core parts of Grit
to be pure Ruby
Basically a Ruby implementation of Git

69. mojombo / grit
And that’s what we run now

70. smoke
Kinda.
Eventually we needed to move of our git repositories off of our web servers
Today our HTTP servers are distinct from our git servers. The two communicate using smoke

71. smoke
“Grit in the cloud”
Instead of reading and writing from the disk, Grit makes Smoke calls
The reading and writing then happens on our file servers

72. bert-rpc
Rather than use Protocol Buffers or Thrift or JSON-RPC, Smoke uses BERT-RPC

73. bert-rpc
bert : erlang ::
json : javascript
BERT is an erlang-based protocol
BERT-RPC is really great at dealing with large binaries
Which is a lot of what we do

74. bert-rpc
we have four file servers, each running bert-rpc servers
our front ends and job queue make RPC calls to the backend servers

75. mojombo / bertrpc
You can grab bert-rpc on GitHub

76. mojombo / bertrpc
Or if you just want to play with BERT

77. chimney
We have a proprietary library called chimney
It routes the smoke. I know, don’t blame me.

78. chimney
All user routes are kept in Redis
Chimney is how our BERT-RPC clients know which server to hit
It falls back to a local cache and auto-detection if Redis is down

79. chimney
It can also be told a backend is down.
Optimized for connection refused but in reality that wasn’t the real problem.

80. proxymachine
All anonymous git clones hit the front end machines
the git-daemon connects to proxymachine, which uses chimney to proxy your
connection between the front end machine and the back end machine (which holds
the actual git repository)
very fast, transparent to you

81. mojombo / proxymachine
proxymachine can be used to proxy any kind of tcp connection
open source

82. ssh
Sometimes you need to access a repository over ssh
In those instances, you ssh to an fe and we tunnel your connection to
the appropriate backend
To figure that out we use chimney

83. jobs
We do a lot of work in the background at GitHub

84. resque
Currently we use a system called Resque.

85. defunkt / resque
You can grab it on GitHub

86. resque
- dealing with pushes
- web hooks
- creating events in the database
- generating GitHub Pages
- clearing & warmingcaches
- search indexing

87. queues
In Resque, a queue is used as both a priority and a localization technique
By localization I mean, “where your workers live”

88. queues
critical,high,low
these three run on our front end servers
Resque processes them in this order

89. queues
page
GitHub Pages are generated on their own machine using the `page` queue

90. queues
archive
And tarball and zip downloads are created on the fly using the `archive` queue
on our archiving machines

91. search
On GitHub, you can search code, repositories, and people

92. solr
Solr is basically an HTTP interface on top of Lucene. This makes it pretty simple
to use in your code.
We use solr because of its ability to incrementally add documents to
an index.

93. Here I am searching for my name in source code

94. solr
We’ve had some problems making it stable but luckily the guys at Pivotal
have given us some tips
Like bumping the Java heap size.
Whatever that means

95. database
Our database story is pretty uninteresting

96. mysql
We use mysql 5

97. master / slave
All reads and writes go to the master
We use the slave for backups and failover

98. caching
On the site we do a ton of caching
using memcached

99. fragments
We cache chunks of HTML all over
Usually they are invalidated by some action

100. fragments
Formerly we invalidated most of our fragments using a generation scheme,
where you put a number into a bunch of related keys and increment it
when you want all those caches to be missed (thus creating new cache
entries with fresh data)

101. fragments
But we had high cache eviction due to low ram and hardware constraints, and found
that scheme did more harm than good.
We also noticed some cached data we wanted to remain forever was being evicted due
to the slabs with generational keys filling up fast

102. page
We cache entire pages using nginx’s memcached module
Lots of HTML, but also other data which gets hit a lot and changes rarely:

103. page
- network graph json
- participation graph data
Always looking to stick more into page caches

104. object
We do basic object caching of ActiveRecord objects such as
repositories and users all over the place
Caches are invalidated whenever the objects are saved

105. associations
We also cache associations as arrays of IDs
Grab the array, then do a get_multi on its contents to get a list of objects
That way we don’t have to worry about caching stale objects

106. walker
We also have a proprietary caching library called Walker

107. walker
It originally walked trees and cached them when someone pushed
But now it caches everything related to git:

108. walker
- commits
- diffs
- commit listing
- branches
- tags
- everything

109. Every git-related page load hits Walker a lot

110. walker
For most big apps, you need to write a caching layer
that knows your business domain
Generic, catch-all caching libraries probably won’t do

111. events
An example of this is our events system

113. This is one fragment

114. Each of these is a fragment

115. They’re also cached as objects

116. As well as a list of ids

117. And that’s just for the dashboard...

118. optimizations
So what other optimizations have we done

119. asset servers
Well we do the common trick of serving assets from multiple subdomains

120. asset servers
assets0.github.com
assets1.github.com
and so forth

121. sha asset id
Instead of using timestamps for asset ids, which may end up hitting the disk
multiple times on each request, we set the asset id to be the sha of the last commit
which modified a javascript or css file

122. sha asset id
/css/bundle.css?197d742e9fdec3f7
/js/bundle.js?197d742e9fdec3f7
Now simple code changes won’t force everyone to re-download the css or js bundles

123. bundling
For bundling itself, we use

124. bundling
yui’s compressor for css and

125. bundling
google’s closure compiler for javascript
we don’t use the most aggressive setting because it means changing
your javascript to appease the compression gods,
which we haven’t committed to yet

126. scripty 301
Again, for most of these tricks you need to really pay
attention to your app.
One example is scriptaculous’ wiki

127. scripty 301
When we changed our wiki URL structure, we setup dynamic 301 redirects
for the old urls.
Scriptaculous’ old wiki was getting hit so much we put the redirect into nginx itself -
this took strain off our web app and made the redirects happen almost instantly

128. ajax loading
We also load data in via ajax in many places.
Sometimes a piece of information will just take too long to retrieve
In those instances, we usually load it in with ajax

131. If Walker sees that it doesn’t have all the information it needs, it kicks off a job
to stick that information in memcached.

132. We then periodically hit a URL which checks if the information is in memcached or not.
If it is, we get it and rewrite the page with the new information.

133. We use this same trick on the Network Graph

134. Fork Queue

135. ajax loading
and anywhere else it makes sense.

136. comet loading
very soon this will all be comet, though

137. monitoring
what do we use for monitoring?

138. nagios
Our support team monitors the health of our machines and core
services using nagios.
I don’t really touch the thing.

139. Here’s a screenshot from my IE browser, complete with the ICQ plugin

140. resque web
We monitor our queue using Resque’s included Sinatra app

142. haystack
We use an in-house app called Haystack to monitor arbitrary information,
tracked as JSON.

143. Here’s an example of Haystack’s “exceptions” view

144. collectd
We also use collectd to monitor load, RAM usage, CPU usage, and other
app-related metrics

145. pingdom
pingdom sends us SMSes when the site is down
it’s nice

146. tender
tender is what we use for customer support

147. it works incredibly well, and they’re constantly improving it

148. testing
Our testing setup is pretty standard

149. test unit
We mostly use Ruby’s test/unit.
We’ve experimented with other libraries including test/spec, shoulda, and RSpec, but in the end
we keep coming back to test/unit

150. git fixtures
As many of our fixtures are git repositories, we specify in the test what sha
we expect to be the HEAD of that fixture.
This means we can completely delete a git repository in one test, then have it back in
pristine state in another. We plan to move all our fixtures to a similar git-system in the future.

151. ci joe
We use ci joe, a continuous integration server, to run on tests after each push.
He then notifies us if the tests fail.

154. defunkt / cijoe
You can grab him at github

155. staging
We also always deploy the current branch to staging
This means you can be working on your branch, someone else can be working on theirs,
and you don’t need to worry about reconciling the two to test out a feature
One of the best parts of Git

156. security

157. github.com/
security
having a security page really helps

158. security@
github.com
we get weekly emails to our security email (that people find on the security page)
and people are always grateful when we can reassure them or a answer their question

159. consultant
if you can, find a security consultant to poke your site for XSS vulnerabilities
having your target audience be developers helps, too

160. backups
backups are incredibly important
don’t just make backups: ensure you can restore them, as well

161. sql
we keep nightly, off-site backups of our sql databases

162. git
and the same for all our git repositories

163. Thanks.
thanks for coming