Building Startups on Scala

buildo's talk at Scala Italy 2015

buildo is a software company enabling startups execute on their vision. In this talk we present our experience in building a solid stack based on Scala for working with multiple startup projects.

Transcript

1. B U I L D I N G S TA R T U P S O N S C A L A T U R N I D E A S I N T O R E A L I T Y @ B U I L D O H Q @ U TA A L @ G A B R O 2 7
2. W H O A R E Y O U ? buildo, a young italian company we help startups everywhere 
 execute on their vision
3. SUSTAINABILITY FAIRNESS QUALITY O U R P I L L A R S
4. L E T ’ S TA K E A S T E P B A C K
5. A L O N G T I M E A G O I N A G A L A X Y FA R FA R AWAY • a wild scary large project appears!
6. F L A S H B A C K : N O T L O N G B E F O R E • Intern at Google, MongoDB • Freelancer • C++ • Python (programming is fun again) • Java (university) • Haskell • Scala
7. F L A S H B A C K : N O T L O N G B E F O R E • Startupper and freelance dev • Java (university) • Objective-C <3 • “blocks? That’s confusing…” • intrigued by Haskell • Scala (Martin’s online course)
8. T H E R E S T O F T H E ( I N I T I A L ) C R E W
9. R E C E N T LY B U R N E D B Y … • a new startup, for hosting and serving videos • a year of work • countless refactors • …node.js
10. B A C K T O O U R S C A RY P R O J E C T • we wanted • type safety • expressiveness • flexibility
11. FA S T- F O R WA R D T O T O D AY
12. B U I L D O , T O D AY • startups, in scala?! • everybody knows rails/node/php is the hipster startup language! • waxed mustache for extra points
13. S TA RT U P T E C H N O L O G I E S 07/08/2014 - source: http://codingvc.com/which-technologies-do-startups-use-an-exploration-of-angellist
14. P E R C E P T I O N • “Do you know Scala?” • “Isn’t it that thing Twitter uses?”
15. P E R C E P T I O N ( C O N T ’ D ) • “developing in scala is slow” • “the learning curve is steep” • “is it worth it for a startup?”
16. S C A L I N G S C A L A D O W N • we started with a large project • and applied what we learned to startups
17. W H Y ? • well, we liked it :-) • small team • the final S in “startups” is not silent
18. O K , W H Y D O Y O U L I K E I T ? • it takes more time to ship code • it takes less time to ship code that works
19. O K , W H Y D O Y O U L I K E I T ? ( C O N T ’ D ) • intrinsic correctness and clarity • easy to write testable code • refactor with confidence • JVM is nice
20. “Scala trusts the programmer to ‘do the right thing’” Martin Odersky (6 hours ago)
21. “Scala trusts the programmer to ‘do the right thing’” Martin Odersky (6 hours ago) “We don’t have enough material on how to get practical on scala” Phil Calçado (short after)
22. behind the scenes
23. H O W D O W E D O T H I S ? 1. dealing with a diverse and evolving set of requirements 2. akka 3. controllers 4. open problems
24. 1 . D E A L I N G W I T H A D I V E R S E S E T O F R E Q U I R E M E N T S
25. M I X - M AT C H I N F R A S T R U C T U R E
26. spray akka slick elastic
 search
27. spray akka slick early stage start-up,
 simple requirements
28. spray akka slick innovation,
 evolved requirements
29. complex system spray akka slick elastic
 search
30. spray akka slick elastic
 search
31. C A K E PAT T E R N
32. C A K E PAT T E R N
33. C A K E PAT T E R N
34. C A K E PAT T E R N
35. cake pattern trait UserService extends DataModule { trait UserServiceDef { def login(username: String, password: String): Option[Token] } def userService: UserServiceDef }
36. cake pattern trait UserService extends DataModule { trait UserServiceDef { def login(username: String, password: String): Option[Token] } def userService: UserServiceDef } trait DataModule { type Token trait DataModuleDef { def getUserByName(username: String): Option[User] def storeToken(user: User, token: Token): Boolean } def dataModule: DataModuleDef }
37. trait MemoryDataModule { self: DataModule => type Token = String object dataModule extends DataModuleDef { val users = new scala.collection.mutable.Map[String, User] val tokens = new scala.collection.mutable.Map[User, Token] def getUserByName(username: String): Option[User] = users.get(username) def storeToken(user: String, token: Token): Boolean = tokens += user -> token } } trait DataModule { type Token trait DataModuleDef { def getUserByName(username: String): Option[User] def storeToken(user: User, token: Token): Boolean } def dataModule: DataModuleDef }
38. trait MemoryDataModule { self: DataModule => … } trait AppUserService { self: UserService => … } object app extends MemoryDataModule with AppUserService println(app.login("utaal", "secretpassword"))
39. router controller mysql mongodb
40. router controller mysql mongodb cassandra
41. router controller mongodb cassandra
42. F R A M E W O R K S
43. N O , T H A N K S github.com/buildo/ingredients
44. // POST /consultation/15/confirm (post & path(“consultations” / IntNumber / “confirm”)) { consultationId => complete(confirmConsultation(consultationId)) } ~ typesafe router
45. • cake pattern • tests • type safety 1 . D E A L I N G W I T H A D I V E R S E S E T O F R E Q U I R E M E N T S
46. 2 . A K K A
47. A S Y N C reactive apps, don’t block a thread per request
48. A K K A akka tell “!”? akka ask “?”? …or not!?
51. • use akka for dispatching requests
 (in spray) • Futures for business logic • Akka for async tasks
 (notifications, elasticsearch updates) 2 . A K K A
52. 3 . C O N T R O L L E R S
53. typesafe router trait ConsultationControllerDef { def confirmConsultation(consultationId: Int): Future[ControllerResponse[Unit]] } // POST /consultation/15/confirm (post & path(“consultations” / IntNumber / “confirm”)) { consultationId => complete( (confirmConsultation(consultationId)) : Future[ControllerResponse[Unit]] ) } ~
54. sealed trait ControllerResponse[+T] object ControllerResponse { sealed trait ControllerError case object NotFound extends ControllerError case class InvalidOperation(desc: String) extends ControllerError case class Forbidden(desc: String) extends ControllerError … … … case class Ok[T](value: T) extends ControllerResponse[T] case class UserError(err: ControllerError) extends ControllerResponse[Nothing] } response semantics
55. def confirmConsultation(consultationId: Int, user: User): Future[ControllerResponse[Unit]] = consultationData.updateStatus( consultationId, ConsultationStatus.Confirmed) map ( throwOnUnmatched { case DataActionResult.Ok(_) => OkEmpty }) controller workflow
56. def confirmConsultation(consultationId: Int, user: User): Future[ControllerResponse[Unit]] = checkRole(user, UserRole.Patient) { checkConsultationExists(consultationId) { c => checkConsultationOwner(c, user) { checkConsultationPending(c) { consultationData.updateStatus( consultationId, ConsultationStatus.Confirmed) map ( throwOnUnmatched { case DataActionResult.Ok(_) => OkEmpty }) } } } } controller workflow
57. def confirmConsultation(consultationId: Int, user: User): Future[ControllerResponse[Unit]] = checkRole(user, UserRole.Patient) { checkConsultationExists(consultationId) { c => checkConsultationOwner(c, user) { checkConsultationPending(c) { consultationData.updateStatus( consultationId, ConsultationStatus.Confirmed) map ( throwOnUnmatched { case DataActionResult.Ok(_) => OkEmpty }) } } } } controller workflow CALLBACK HELL
58. sealed trait ControllerResponse[+T] object ControllerResponse { sealed trait ControllerError case object NotFound extends ControllerError case class InvalidOperation(desc: String) extends ControllerError case class Forbidden(desc: String) extends ControllerError … … … case class Ok[T](value: T) extends ControllerResponse[T] case class UserError(err: ControllerError) extends ControllerResponse[Nothing] } response semantics
59. monadic controllers type CtrlFlow[A] = CtrlError \/ A sealed trait CtrlError object CtrlError { case class InvalidOperation(desc: String) extends CtrlError case class Forbidden(desc: String) extends CtrlError case object NotFound extends CtrlError … … … }
60. def confirmConsultation(consultationId: Int, user: User): FutureCtrlFlow[Unit] = for { _ <- eitherT(checkRole(user, UserRole.Patient).point[Future]) c <- checkConsultationExists(consultationId) _ <- checkConsultationOwner(c, user) _ <- checkConsultationPending(c) res <- eitherT(consultationData.updateStatus(consultationId, ConsultationStatus.Confirmed).map(_.point[CtrlFlow])) } yield { throwIfNotOk(res) Ok(()) } monadic controllers type FutureCtrlFlow[B] = EitherT[Future, CtrlError, B]
62. • monad! • non-trivial to design,
 straightforward to use 3 . C O M P L E X C O N T R O L L E R L O G I C
63. 4 . O P E N P R O B L E M S
64. M O D U L A R I T Y • modularity comes with a cost • boilerplate to translate between internal and external representations • we can’t trace a request across different layers
65. P E O P L E • you can’t throw developers at this • you need good programmers • scala is (still) a good hiring signal
66. Good programmers are up to 30 times better than mediocre programmers, according to “individual differences” research. Given that their pay is never commensurate, they are the biggest bargains in the software field. Robert L. Glass
67. @milanoscala
68. Thank you, questions? @buildoHQ @utaal @gabro27
69. Thank you, questions? @buildoHQ @utaal @gabro27