Introduction to Erlang and OTP

1. 1 hour dive into
Erlang/OTP
@jvalduvieco @jordillonch

2. Problem domain

3. Lots of users

4. Lots of users

5. 24x7x365

6. 24x7x365

7. Lots of critical concurrent
transactions

8. Lots of critical concurrent
transactions

9. Hardware or software
breaks

10. Hardware or software
breaks

11. Lots of code changes

12. Lots of code changes

13. Unscalable
Unmaintainable } code

14. Unscalable
Unmaintainable } code

15. Maintenance/Debug
in
production system

16. Maintenance/Debug
in
production system

17. Does it sound to you?

18. The Erlang solution

19. Simplicity...

20. Minimize defensive
programming

21. Typeless variables

22. Develop by contract

23. t-shirt function
size
If

24. a

25. function

26. does

27. not

28. fit

29.
on

30. your

31. t-shirt

32. it

33. is

34. too

35. long!

36. Single responsibility
principle

37. No shared state
between entities

38. High Concurrency

39. High Concurrency
High concurrency

40. Light threads

41. Light threads
hundreds of thousands of threads in one
machine with a good cpu scheduler

42. Light threads
hundreds of thousands of threads in one
machine with a good cpu scheduler
Lt
Lt
Lt

43. Message passing
Lt
Lt
Lt

44. Message passing
A shared nothing architecture that
communicates through message passing
Lt
Lt
Lt

45. Message passing
A shared nothing architecture that
communicates through message passing
Lt
Lt
Lt

46. Process Mailbox
Lt
Lt
Lt

47. Process Mailbox
Every process has a mailbox with incoming
messages, process take on convenience
Lt
Lt
Lt

48. No shared state
Lt
S
Lt
S
Lt
S

49. No shared state
Every process its own internal state stored in
a variable avoiding lock contention
Lt
S
Lt
S
Lt
S

50. Soft realtime

51. Soft realtime
You have no strict guarantees on
latency but language is designed
to have low latency

52. High availability

53. High availability
High availability

54. Supervised processes
Pa
Pb

55. Supervised processes
processes can be monitored by other
processes, handling its termination
Pa
Pb

56. Fail early
Pa
Pb
S

57. Fail early
Fail as soon as possible and let someone
handle bad data, someone will restart you
Pa
Pb
S

58. Fail early
Fail as soon as possible and let someone
handle bad data, someone will restart you
Pa
Pb2
S

59. Hot code update
Pb
Pa v1
S
Pc

60. Hot code update
processes code and data can be replaced
without loosing service
Pb
Pa v1
S
Pc

61. Hot code update
processes code and data can be replaced
without loosing service
Pb
Pa v1
v2
S
Pc

62. Distribution
Node Node
P P P P
P P P P
P P P P

63. Distribution
Processes run on nodes and can be located
wherever they are
Node Node
P P P P
P P P P
P P P P

64. How does it look like?

66. Show me the code!

67. Demo 1

68. Hands on

69. The shell

70. Type on your console:
erl

71. You should see:
Erlang R16B (erts-5.10.1) [source] [64-bit]
[smp:2:2] [async-threads:10] [hipe] [kernel-
poll:false] [dtrace]
Eshell V5.10.1 (abort with ^G)
1

72. Variables

73. Variables start
Uppercase

74. Variables are immutable

75. Can contain any type

76. You can do things like...

77. 1 Foo = 1.
1
2 Foo = 2.
** exception error: no match of right hand
side value 2

78. Foo

79. is

80. bounded

81. to

82. 1
1 Foo = 1.
1
2 Foo = 2.
** exception error: no match of right hand
side value 2

83. Foo

84. is

85. bounded

86. to

87. 1
1 Foo = 1.
1
Foo

88. ==

89. 2

90. ?
2 Foo = 2.
** exception error: no match of right hand
side value 2

91. 1 Foo = 1.
1
2 Bar = 2.
2
3 Foo = Bar.
** exception error: no match of right
hand side value 2

92. This is GREAT!

93. Now you have your
basic error checking
system implemented

94. Advanced
types

95. [List]

96. [1,2,3,4,5,6]

97. You can do things like...

98. Iterate sequentially

99. 1 MyList = [1,2,3,4].
[1,2,3,4]
2 [Head|Tail] = MyList.
[1,2,3,4]
3 Head.
1
4 Tail.
[2,3,4]

100. 1 MyList = [1,2,3,4].
[1,2,3,4]
2 [Head|Tail] = MyList.
[1,2,3,4]
3 Head.
1
4 Tail.
[2,3,4]

101. 1 MyList = [1,2,3,4].
[1,2,3,4]
2 [Head|Tail] = MyList.
[1,2,3,4]
3 Head.
1
4 Tail.
[2,3,4]

102. Do something to all or
some items on a list
(list comprehensions)

103. 1 MyList = [1, 2, 3, 4].
[1,2,3,4]
2 [X + 2 || X - MyList, X 2].
[5,6]

104. [Strings]

105. A list

106. You can do things like...

107. 1 MyString = Erlang is not Ruby.
Erlang is not Ruby

108. 1 MyString = Erlang is not Ruby.
Erlang is not Ruby
2 [Head2|Tail2] = MyString.
Erlang is not Ruby
3 Head2.
69 ASC

109. =

110. “E”
4 Tail2.
rlang is not Ruby

111. {Tuples}

112. {1,2,3}

113. Basic data container

114. random access

115. matcheable

116. You can do things like...

117. 1 Mytuple = {1,2,3,4}.
{1,2,3,4}
2 A = 1.
1
3 B = 2.
2
4 {A,B,C,D} = {1,2,3,4}.
{1,2,3,4}
5 C.
3
6 D.
4

118. 1 Mytuple = {1,2,3,4}.
{1,2,3,4}
2 A = 1.
1 A

119. and

120. B

121. are
3 B = 2. bounded

122. variables
2
4 {A,B,C,D} = {1,2,3,4}.
{1,2,3,4}
5 C.
3
6 D.
4

123. 1 Mytuple = {1,2,3,4}.
{1,2,3,4}
2 A = 1.
1 A

124. and

125. B

126. are
3 B = 2. bounded

127. variables
2
4 {A,B,C,D} = {1,2,3,4}.
{1,2,3,4}
5 C. pattern

128. matching
3 A==1?
6 D. B==2?
4

129. 1 Mytuple = {1,2,3,4}.
{1,2,3,4}
2 A = 1.
1 A

130. and

131. B

132. are
3 B = 2. bounded

133. variables
2
4 {A,B,C,D} = {1,2,3,4}. C

134. and

135. D

136. are

137.
{1,2,3,4}
unbounded

138.
5 C. pattern

139. matching
variables
3 A==1?
6 D. B==2?
4

140. functions

141. functions are types

142. single exit point

143. You can do things like...

144. foo_bar_func(Foo, Bar) -
Result = Foo + Bar,
Result.

145. This

146. is

147. a

148. arity

149. 2

150. function

151.
(2

152. parameters)
foo_bar_func(Foo, Bar) -
Result = Foo + Bar,
Result.

153. This

154. is

155. a

156. arity

157. 2

158. function

159.
(2

160. parameters)
foo_bar_func(Foo, Bar) -
Result = Foo + Bar,
Result.
means

161. that

162. more

163.
code

164. is

165. to

166. come

167. This

168. is

169. a

170. arity

171. 2

172. function

173.
(2

174. parameters)
foo_bar_func(Foo, Bar) -
Result = Foo + Bar,
Result.
means

175. that

176. more

177.
code

178. is

179. to

180. come
means

181. the

182. function

183.
code

184. has

185. ended

186. This

187. is

188. a

189. arity

190. 2

191. function

192.
(2

193. parameters)
foo_bar_func(Foo, Bar) -
Result = Foo + Bar,
Result.
means

194. that

195. more

196.
code

197. is

198. to

199. come
Single

200. exit

201. point
Returns

202. Result
means

203. the

204. function

205.
code

206. has

207. ended

208. 1 FooBar = fun(Foo, Bar) -
1 Foo + Bar
1 end.
#Funerl_eval.12.82930912
2 Result = FooBar(1, 2).
3

209. atoms

210. A constant with name

211. lowercase

212. You can do things like...

213. 1 ok.
ok
2 ko.
ko
3 ok =:= ko.
false
4 ok =:= ok.
true

214. 1 MyFuncOK = fun() - {ok, 33} end.
#Funerl_eval.20.82930912
2 MyFuncFail = fun() - {error, bad_arg} end.
#Funerl_eval.20.82930912
3 {ok, Result} = MyFuncOK().
{ok,33}
4 {ok, Result2} = MyFuncFail().
** exception error: no match of right hand
side value {error,bad_arg}

215. atoms
1 MyFuncOK = fun() - {ok, 33} end.
#Funerl_eval.20.82930912
2 MyFuncFail = fun() - {error, bad_arg} end.
#Funerl_eval.20.82930912
3 {ok, Result} = MyFuncOK().
{ok,33}
4 {ok, Result2} = MyFuncFail().
** exception error: no match of right hand
side value {error,bad_arg}

216. atoms
1 MyFuncOK = fun() - {ok, 33} end.
#Funerl_eval.20.82930912
2 MyFuncFail = fun() - {error, bad_arg} end.
#Funerl_eval.20.82930912
}
3 {ok, Result} = MyFuncOK().
{ok,33} error
4 {ok, Result2} = MyFuncFail(). checking
** exception error: no match of right hand
side value {error,bad_arg}

217. atoms
1 MyFuncOK = fun() - {ok, 33} end.
#Funerl_eval.20.82930912
2 MyFuncFail = fun() - {error, bad_arg} end.
#Funerl_eval.20.82930912
}
3 {ok, Result} = MyFuncOK().
{ok,33} error
4 {ok, Result2} = MyFuncFail(). checking
** exception error: no match of right hand
side value {error,bad_arg}
do

218. they

219. match?

220. modules

221. basic name spacing

222. public/private functions

223. You can do things like...

224. On your ${EDITOR} create cool_func.erl
-module(cool_func).
-export([foo_bar_func/2]).
foo_bar_func (Foo, Bar) -
Result = Foo + Bar,
{ok, Result}.

225. On erlang shell type:
1 c(cool_module).
{ok,cool_module}
2 {ok, Result3} = cool_module:sum(33, 44).
{ok,77}
3 Result3.
77

226. Too easy?
Let’s add some pattern
matching on parameters!

227. area({square, Side}) -
{ok,Side * Side};
area({circle, Radius}) -
% almost :-)
{ok, 3 * Radius * Radius};
area({triangle, A, B, C}) -
S = (A + B + C)/2,
{ok, math:sqrt(S*(S-A)*(S-B)*(S-C))};
area(Other) -
{error, invalid_object}.

228. area({square, Side}) -
{ok,Side * Side}; means

229. that

230. there

231. is

232.
area({circle, Radius}) - another

233. matching

234.
% almost :-) posibility
{ok, 3 * Radius * Radius};
area({triangle, A, B, C}) -
S = (A + B + C)/2,
{ok, math:sqrt(S*(S-A)*(S-B)*(S-C))};
area(Other) -
{error, invalid_object}.

235. area({square, Side}) -
{ok,Side * Side}; means

236. that

237. there

238. is

239.
area({circle, Radius}) - another

240. matching

241.
% almost :-) posibility
{ok, 3 * Radius * Radius};
area({triangle, A, B, C}) -
S = (A + B + C)/2,
{ok, math:sqrt(S*(S-A)*(S-B)*(S-C))};
area(Other) -
{error, invalid_object}.
mymodule:area({square, 10}).
mymodule:area({circle, 10}).
mymodule:area({triangle, 2, 2, 3.5}).

242. Want more?
Let’s add some recursion!

243. Want more?
Let’s add some recursion!
Erlang does not use loops

244. factorial(0) - 1;
factorial(N) - N * factorial(N-1).

245. OTP

246. Oh, This is Perfect!

247. OTP is a set of rock solid
architecture patterns,
practices and tools

248. Improves the design,
fault tolerance and
deployment of your app

249. Erlang is just a language,
OTP makes it great for
the real world

251. Basic architecture
patterns

252. Supervisor
S
P P P S
P P

253. Supervisor
S
P P P S
P P

254. Supervisor spawns processes
and handles its death

255. gen_server
P
P gs
P

256. gen_server
P
P gs
P

257. Generic single threaded server

258. gen_fsm
P
P gf{S}
P

259. gen_fsm
P
P gf{S}
P

260. Generic Finite State Machine

261. gen_event
P
P P
em
P P
P

262. gen_event
P
P P
em
P P
P

263. Event handler, you can
subscribe to events

264. More on OTP...
• File hierarchy
• Applications
• Releases
• Basic abstraction libraries (logging,
system...)

265. Let’s see a gen_server
in action!

266. Introducing
Simple Key Value Store

267. A server that is able to
store {Key,
Value} and retrieve
them by Key

268. Demo II

269. skvs diagram
S
P gs
ets

270. skvs diagram
S
P gs
ets

271. Starting skvs
Go to skvs source directory
Compile
./rebar compile
Start the Erlang node
erl -pa ebin
Start the app
application:start(skvs).

272. Some commands
Set a value
skvs_server:set(“Key”,”Value”).
skvs_server:set(“Key2”,”Value2”).
Get a value
skvs_server:get(“Key2”).

273. Code on client: skvs_server.erl
start_link() -
gen_server:start_link({local, skvs},
skvs_server, [], []).
get(Key) -
gen_server:call(skvs, {get, Key}).
set(Key,Value) -
gen_server:call(skvs, {set, Key, Value}).
set_fire_and_forget(Key,Value) -
gen_server:cast(skvs, {set, Key, Value}).

274. Code on client: skvs_server.erl
start

275. gen_server
start_link() -
gen_server:start_link({local, skvs},
skvs_server, [], []).
get(Key) -
gen_server:call(skvs, {get, Key}).
set(Key,Value) -
gen_server:call(skvs, {set, Key, Value}).
set_fire_and_forget(Key,Value) -
gen_server:cast(skvs, {set, Key, Value}).

276. Code on client: skvs_server.erl
start

277. gen_server
start_link() -
gen_server:start_link({local, skvs},
skvs_server, [], []).
get(Key) -
gen_server:call(skvs, {get, Key}).
sync

278. call

279. to

280. server
set(Key,Value) - (waits

281. for

282. reply)
gen_server:call(skvs, {set, Key, Value}).
set_fire_and_forget(Key,Value) -
gen_server:cast(skvs, {set, Key, Value}).

283. Code on client: skvs_server.erl
start

284. gen_server
start_link() -
gen_server:start_link({local, skvs},
skvs_server, [], []).
get(Key) -
gen_server:call(skvs, {get, Key}).
sync

285. call

286. to

287. server
set(Key,Value) - (waits

288. for

289. reply)
gen_server:call(skvs, {set, Key, Value}).
set_fire_and_forget(Key,Value) -
gen_server:cast(skvs, {set, Key, Value}).
async

290. call

291. to

292. server
(fire

294. forget)

295. Callback code: skvs_server.erl
%% Client Callbacks on server
%% Sync calls, expects response
handle_call({set, Key, Value}, _From,State) -
{reply, set_value(Key,Value), State};
handle_call({get, Key}, _From, State) -
{reply, get_value(Key), State}.
%% Async calls, do not expect response
handle_cast({set, Key, Value}, State) -
set_value(Key,Value),
{noreply, State}.

296. Callback code: skvs_server.erl
%% Client Callbacks on server
%% Sync calls, expects response
handle_call({set, Key, Value}, _From,State) -
{reply, set_value(Key,Value), State};
handle_call({get, Key}, _From, State) -
{reply, get_value(Key), State}.
%% Async calls, do not expect response
handle_cast({set, Key, Value}, State) -
set_value(Key,Value),
{noreply, State}.
return

297. value

298. Callback code: skvs_server.erl
%% Client Callbacks on server
%% Sync calls, expects response
handle_call({set, Key, Value}, _From,State) -
{reply, set_value(Key,Value), State};
handle_call({get, Key}, _From, State) -
{reply, get_value(Key), State}.
%% Async calls, do not expect response
handle_cast({set, Key, Value}, State) -
set_value(Key,Value),
{noreply, State}.
Survives

299. between

300.
return

301. value requests

302. Actual work...: skvs_server.erl
%% Private functions
set_value(Key, Value) -
% Insert Key, Value into ETS.
% Fail early
{ok,Result}=case ets:insert(data_store,{Key,Value}) of
true -
{ok, {Key,Value}};
{error, Reason} -
{error, Reason}
end,
Result.

303. Actual work...: skvs_server.erl
%% Private functions
set_value(Key, Value) -
% Insert Key, Value into ETS.
% Fail early
{ok,Result}=case ets:insert(data_store,{Key,Value}) of
true -
{ok, {Key,Value}};
{error, Reason} -
{error, Reason}
end, ETS

304. is

305. a

306. Key

307. value

308. store

309.
Result. in

310. RAM

311. Use cases

312. Gaming Industry

313. Gaming Industry

314. Messaging / IM

315. Messaging / IM

316. Payments

317. Payments

318. Databases

319. Databases

320. Others

321. Others

322. Some day...

323. Every highly interactive
website? ;)

324. Pay Hello
Ouch!
Every highly interactive
website? ;)
Would you...
Hey
NO! ! Hi
Buf

325. Internet of things

326. And now what?

327. Install Erlang/OTP!
https://www.erlang-solutions.com/downloads/download-erlang-otp

328. Use a great IDE
• IntelliJ + Erlang (plugin)
• Sublime Text + SublimErl
• Emacs

329. Read some books

330. RTFM
• http://www.erlang.org/doc.html
• http://erldocs.com/

331. Join mailing lists
• Official Erlang mailing list
• http://erlang.org/mailman/listinfo/erlang-
questions
• Join Barcelona Erlang user group on google
groups

332. Find know-how
• Check http://www.erlang-factory.com/
videos
• Search for Erlang conferences on slideshare
• Pray for an http://erlangcamp.com/ near
your city

333. Read some code

334. This is the result of 6 months
of fun learning Erlang/OTP

335. We are looking for awesome
projects
http://es.linkedin.com/in/jvalduvieco
http://es.linkedin.com/in/jllonch

336. Thank you!
https://github.com/jvalduvieco/betabeers_201303

337. Thank you!
https://github.com/jvalduvieco/betabeers_201303
we

338. hope

339. you

340. feel

341.
like

342. him

343. :)
(we

344. did)

345. Erlang, The Movie
http://www.youtube.com/watch?v=uKfKtXYLG78

346. Images sources
http://diromero.wordpress.com/2011/10/07/home-automation/
http://iffergan.com/
http://technode.com/2012/05/14/internet-of-things-not-just-a-concept-for-fund-raising/
http://modernherstory.wordpress.com/2011/05/18/open-minds-open-hearts/
http://www.i-m.co/eviemouse/problemsolved/
http://strategicsalesmarketingosmg.wordpress.com/2012/06/25/who-are-twitter-users/
http://www.secureworks.com/it_security_services/advantage/soc/
http://labourlist.org/2011/11/my-biggest-worry-about-labour%E2%80%99s-future/broken-chain/
http://prothemedesign.com/how-to/why-you-should-keep-wordpress-and-your-plugins-up-to-date/attachment/matrix-code-
update/
http://thegapbetweentwoworlds.com/category/career-transition
http://www.wingweb.co.uk/Images/697/KC-10_Extender_SR-71_Blackbird
http://www.tonywoodtraining.com/2010/11/29/motivation-to-exercise-and-eat-right/
http://portalmie.com/blog/6/2011/09/kushimoto-diving-park-tokushima-revista-no-7/
http://www.bcsagroup.com/
http://www.losemyaccent.com/tag/hand/
http://articulo.mercadolibre.com.ar/MLA-450970296-cortaplumas-victorinox-huntsman-15-usos-navaja-origen-suizo-_JM
http://openclipart.org/detail/4112/
http://blog-en.coaching-go.com/2012/02/learn-to-say-no-and-know-how-to-say-yes/ok-2/
http://en.wikipedia.org/wiki/File:We_Can_Do_It!.jpg
http://triniblog.wordpress.com/tag/laberintos/
http://www.catskillsnyrealestate.com/Want-More-Info-Catskill-Real-Estate.php
http://www.thelovelyplanet.net/lush-green-images-planet-earth/
http://www.growthmax.com/how-exactly-does-growthmax-plus-make-you-grow-taller/
http://www.ayurvedalive.in/keep-your-eyes-healthy-beautiful
http://my.mmosite.com/510619/blog/item/lord_of_the_rings_online.html
http://scifistorm.org/2010/03/24/lord-of-the-rings-blu-ray-review/
http://www.123rf.com/photo_15612022_3d-cartoon-bug.html
http://www.airliners.net/photo/1134244/L/
http://www.muypymes.com/2009/12/04/moleskine-mucho-mas-que-una-agenda-personal
http://learnyousomeerlang.com/the-hitchhikers-guide-to-concurrency
http://planetpooks.com/one-more-reason-to-love-hermiones-handbag/