Voxxed Days Ticino 2018

1. Playtrip: a CQRS/ES
architecture in Erlang
Nicola Fiorillo
consultant software engineer and architect
Erlang/Elixir evangelist
playtrip Sagl

2. www.nicolafiorillo.com
C/C++

3. ERLANG +
CQRS +
ES =
PLAYTRIP
Summary

4. survey

5. www.play-trip.com

8. Travelers: 287
Storytellers: 153
Published stories: 80
Events: +10K

9. dashboard
storyteller
dashboard
storyteller
manager
dashboard
administrator
iOS/Android
traveler
MongoDB
backend
API REST Commands/Queries
create stories
validate stories
admin and data
enjoystories

15. 1986
Joe Armstrong,Robert Virding,Mike Williams
almost-zero downtime

16. Erlang challenges
• live update
• concurrency
• scalability
• fault-tolerance
• distribution
• high availability

17. 1998: open source

19. José Valim,a Ruby Core developer
2011
https://elixir-lang.org/

20. Elixir
• fully Erlang compatible
• (non pure) functional programming: pattern
matching,immutability,tail recursion,pipes,ecc.
• extensibility,DSLs,meta-programming: macro
• ecosystem: MIX
• interactive development: IEx
• built-in unit testing
• built-in documentation

22. What Elixir brings to the table
is a complete different surface
syntax […]. What you might
call a “non-scary" syntax, and
a load of extra goodies.
Joe Armstrong

23. Names
• OTP (Open Telecom Platform)
• Erlang
• Elixir
• BEAM (Bogdan/Björn’s Erlang Abstract
Machine)

24. BEAM
• transparent SMP/multi-core support (built-in load balancing)
• everything is a process
• processes are strongly isolated
• process creation and destruction is a lightweight operation
• message passing is the only way for processes to interact,
asynchronous communication
• processes have unique names
• no global data

25. Process
• links,monitors,and supervisors
• speed
OS process init: 1ms,1 MB/2 MB
BEAM process init: 1µs/2µs,1kB/2kB
• container of state
• garbage collection at process level
• can be distributed across cores

26. THE SYSTEM MUST NEVER GO DOWN!
Part may crash and burn but…

27. in BEAM the unit of concurrency is the process
and the process implements the Actor Model

28. Actor Model
The Actor Model is a conceptual model to
manage concurrency,defining general rules
about interaction among actors.

29. Actor Model
• mailbox,all messages are processed sequentially
• independence
• unique reference
• no shared memory
• (can) have private state
• state not alterable by other actors
• asynchronous messages communication

30. Actor 1
Actor 2
Actor 3
mailbox
mailbox
mailbox

31. Why this “revival”?

32. Moore’s law
Moore's law is the observation that the
number of transistors in a dense
integrated circuit doubles about every
12 18 24 months

34. Command Query Responsibility Segregation
and Event Sourcing

35. UI
read/write persistence

36. ?UI
command model
write persistence
query model
read persistence

37. UI
command model
query model
query A
event busevent(s)
persistence
query B
query N
unique source
of truth

38. CQRS/ES
• respond to future business requests
• max read/write efficiency
• inspect the past states
• true history

39. domain event
command
aggregate
service
projection
policy
UI
event bus
From picture that explains everything
©ZioBrando

40. BEAM +
ELIXIR +
CQRS +
ES =
PLAYTRIP

41. <0, 38, 0>
request process
dashboard
storyteller
save_story(story_data)
HTTP
command bus
registry
process
aggregate
aggregate
aggregatestory
aggregate
aggregate name + story_id-> PID
story
process
<0, 42, 0>
state
story_saved(story_data)
event bus
process
handle_command(:save_story,story_data)
projectionprojectionprojectionstories
projection
HTTP
<0, 40, 0>
<0, 26, 0>
<0, 28, 0>

44. Application
Supervisor
:persistence
MongoDB
:event_store
Business
Supervisor
:entities:entitiesservices
:entities:entitiesprojections
:entities:entitiesaggregates:registry
playtrip supervisor tree

45. • Introducing EventStorming,Alberto Brandolini: https://leanpub.com/
introducing_eventstorming
• Domain Driven Design,CQRS,and Event Sourcing video course by Greg Young: http://
subscriptions.viddler.com/GregYoung
• Reactive Design Patterns,Kuhn,Hanafee,Allen: https://www.manning.com/books/reactive-
design-patterns
• Programming Elixir 1.6,Dave Thomas: https://pragprog.com/book/elixir16/programming-
elixir-1-6
• The Little Elixir & OTP Guidebook,Tan Wei Hao: https://www.manning.com/books/the-little-
elixir-and-otp-guidebook
• Learn You Some Erlang for great good!,Fred Hebert: https://learnyousomeerlang.com/
• Stuff Goes Bad Erlang in Anger,Fred Hebert: http://www.erlang-in-anger.com/
• CQRS/ES in Elixir,Nicola Fiorillo: (soon on Leanpub…)
In the white rabbit hole

46. Playtrip: a CQRS/ES
architecture in Erlang
Nicola Fiorillo
consultant software engineer and architect
Erlang/Elixir evangelist
playtrip Sagl