JS meetup of Open Tech Week by Sigma Software, Odessa 2019

1. The working architecture of
NodeJs applications
Viktor Turskyi

2. Viktor Turskyi
● CEO and principal architect at
WebbyLab
● Open source developer
● More than 15 years of experience
● Delivered more than 60 projects of
different scale
● Did projects for 5 companies from
Fortune 500 list

3. Why do I talk about architecture?
● The importance of good architecture is often underestimated.
● There are a lot of “Hello, world” tutorials for NodeJs but no one explain how to
build a large scale project.
● A lot of frontend developers want to be full stack but do know how to structure
backend code.
● I want to share our experience with the community

4. Why do I call it the working architecture?
● It is in production for 8 years.
● It is battle tested with more than 60 projects of different scale.
● It proved itself as working approach in NodeJs, PHP, Perl web application

5. During this talk I will:
● I will answer what to choose Monolith or Microservices?
● Will answer which web-framework to choose.
● Explain basic ideas behind the architecture
● Show real code, not only diagrams.

6. Monolith or Microservices by default?

7. What is the most popular architecture
today?

8. Big Ball of Mud
http://www.laputan.org/mud/mud.html#BigBallOfMud

9. If Monolith is a big ball of mud.
Will it be better with Microservices?

10. Microservices:
Big and distributed ball of mud

12. "If you cannot build a monolith what makes you think that you
can build Distributed Microservices"
Simon Brown

14. Microservice architecture visualized
https://twitter.com/ThePracticalDev/status/845285541528719360

15. Microservices drawbacks
● High operational complexity (increases costs)
● Versions compatibility issues (harder to track all dependencies in consistent
state, reduces iterations speed)
● Extremely hard to support transactions (risks of inconsistencies)
● Distribution issues (harder to program)
● Traceability issues (harder to debug)
● Technology diversity (mixing languages increases support costs,
standardization issues, hiring issues etc)
● You need more experienced team (hiring issues)

16. Key microservices issue

17. What is the best architectural decision?

18. Robert Martin:
“The job of architect is not to make decision, the job of
the architect is to defer decisions as long as possible”
“Good architecture maximizes number of decisions not
made”
https://www.youtube.com/watch?v=o_TH-Y78tt4

19. Martin Fowler:
● But when your components are services with remote communications, then
refactoring is much harder than with in-process libraries.
● Another issue is If the components do not compose cleanly, then all you are
doing is shifting complexity from inside a component to the connections
between components. Not just does this just move complexity around, it
moves it to a place that's less explicit and harder to control.
https://martinfowler.com/bliki/MonolithFirst.html

20. So, we start with monolith in 90% of
cases

21. What is Monolith?

22. Usually it looks like

24. Which web-framework to choose?

25. NodeJs frameworks
● Express
● Koa
● Sails
● Nest
● Feathers
● Derby
● Kraken
● Hapi
● etc

26. It doesn’t matter!

27. Your application architecture should not depend on a
web framework

28. Web frameworks we use
NodeJs: Express
PHP: Slim3
Perl : Mojolicious

29. “We use MVC why do we need another
architecture?”

30. MVC (from wikipedia)

31. Where to place this code? Model or Controller?

32. Fat Stupid Ugly Controllers
“The M in MVC: Why Models are Misunderstood and Unappreciated” Pádraic
Brady
http://blog.astrumfutura.com/2008/12/the-m-in-mvc-why-models-are-misunderstoo
d-and-unappreciated/

33. Is Model (MVC) and Domain Model the same?

34. Model (from MVC)/Domain Logic
● Domain model
● Transaction script
● Table module
● Service layer

35. Domain model
An object model of the domain that incorporates both
behavior and data. (M. Fowler)
Works well for medium and large applications

36. Transaction script
Organizes business logic by procedures where each
procedure handles a single request from the presentation (M.
Fowler).
Works well for small projects

38. Controllers
Services
Domain model
Data access
layer
Dispatcher

40. The way of thinking about Controllers
● Extremely thin layer
● Protects underneath layers from everything related to HTTP
● If you change JSON to XML (or even CLI), only controllers should be rewritten

41. The way of thinking about Domain Model
● Belongs to Model layer of MVC
● The core part of your application
● You have almost all of your business logic here (not only database access)!!!
● Knows nothing about service layer and upper layers
● Responsible for data storing and data integrity
● Fine grained API (not suited for remote invocation)

42. The way of thinking about Services
● Belongs to Model layer of MVC
● Contains application logic
● Does not trust any incoming params
● You should keep thin if possible
● Knows nothing about controllers/transport/UI.
● Use cases based API
● Knows about context (what user asks for data)
● Knows when and how to notify user (emails etc)
● Does coordination and security
● Coarse grained API (well suited for remote invocation)

43. Core patterns in the architecture
Application level (Martin Fowler):
● MVC
● Service layer
● Domain model
Class level (GoF):
● Template method
● Command

44. How do we cook the service layer?

45. Rule 1: Separate service class (implemented a
command) for each endpoint

46. Real code (with meta programming)

47. NodeJs example of a Service class

48. Base class (the simplest version)

50. “run” method
Template method in base class
Guarantees that all procedures are kept:
● Data was validated
● “execute” will be called only after validation
● “execute” will receive only clean data
● Checks permissions before calling “execute”
● Throws exception in case of validation errors.
Can do extra work like caching validator objects, etc.

51. Rule 2: Never return objects directly
Whitelist every object
property:
1. You know what you return
(that no internal/secret
data there)
2. Your API is stable

52. Rule 3: There is no excuse for not using Promises or
await/async today
● Error handling - one of the most powerful promise features. You can structure
your error processing in a much better way with promises.
● You will never see “uncaughtException”
● You will have manageable code

53. Rule 4: Unified approach to validation
● DO NOT TRUST ANY USER INPUT! NEVER!!!
● Declarative validation
● Exclude all fields that do not have validation rules described
● Returns understandable error codes (neither error messages nor numeric
codes)
● It should be clear for the service user what is wrong with his data

54. We use LIVR for the validation
It supports:
● JavaScript
● Perl
● Perl 6
● PHP
● Go
● Erlang
● Python
● Ruby
● Java
● Lua
Details are here - http://livr-spec.org/

55. It should be clear where any code should be! Otherwise you do not architecture.
One of the risks, than you can end up with an “Anemic domain model”
(https://www.martinfowler.com/bliki/AnemicDomainModel.html)
If you have a large project, this can be a reason of project failure as you will
implicitly switch to “transaction script” approach which is not well suited for large
applications.
Rule 5: Be aware of “Anemic domain model”
antipattern

56. Perl example of a Service class

59. GraphQL support

62. Full example: User registration

63. User registration: controller/dispatcher

64. Controllers

65. Service

67. User model

68. Action model

69. Main benefits
● NodeJs, PHP, Perl - the same architecture.
● Works with small and large projects
● Extremely flexible.
● Ease to start.
● Much cheaper for company to support the same approach on all projects.
● Web framework agnostic and based on micro frameworks which is easy to learn for
new person.
● Cheaper technology switch (for example from PHP to NodeJs).
● Cheaper communication.
● Knowledge sharing (larger core).
● Higher resources utilization.
● Monolith first approach and modular architecture allows us to switch to Microservices
later

70. FAQ
Q: Do we use 12-factor approach?
A: Yes, it is a part of boilerplate.
Q: Is it ok to call a service from service
A: We do not do this. If you need the same logic reuse, possibly it should go to Domain
Model.
Q: Is it ok to place methods in sequelize models?
A: Yes, it the idea of any ORM! Otherwise it will be Anemic Domain Model

71. Useful links
MonolithFirst by Martin Fowler
Microservice Trade-Offs by Martin Fowler
PresentationDomainDataLayering by Martin Fowler
The Principles of Clean Architecture by Uncle Bob Martin
The Clean Architecture by Robert Martin
Microservice Architecture at Medium
https://12factor.net/

72. NodeJs Starter Kit (this year)
● Based on ideas of Clean Architecture
● Works with small and large projects
● Follows 12 factor app approach
● Modern JS (including ES6 for Sequalize)
● Supports both REST API and GraphQL
● Follows security best practices.
● Docker support
● Covered with tests
● Battle tested
● Built on top of express.js
● Users management

73. Telegram: @JABASCRIPT

74. Viktor Turskyi
@koorchik