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Poznan Elixir Meetup #6 mkaszubowski94

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Time

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Time Development speed

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Time Software quality

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Time Developer happiness

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Time ?

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Time The big rewrite

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Time

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Time

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Software Architecture Poznan Elixir Meetup #6 mkaszubowski94

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*Disclaimer

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What is software architecture?

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"the important stuff Ralph Johnson

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"the important stuff (whatever that is)" Ralph Johnson

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"The goal of software architecture is to minimize the human resources required to build and maintain the required system." Robert C. Martin, "Clean Architecture"

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Architecture is about taking a step back, looking at a bigger picture and being aware of trade-offs when making decisions.

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Quality attributes (non-functional requirements)

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Quality attributes Maintainability Reusability Availability Performance Reliability Scalability Security Supportability Testability Deployability Simplicity Development speed Composability Fault tolerance ...

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Security Usability

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Common architecture patterns

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Monolith architecture

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Layered architecture

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Layered architecture

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Typical layered architecture

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Hexagonal architecture

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Clean architecture

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Clean architecture

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Microservices architecture

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Event-driven architecture

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Serverless architecture

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Of course you can mix them

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Example: ISO/OSI model

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‣ Isolation ‣ Separation of concerns ‣ Hiding of implementation details ‣ Good abstractions ISO/OSI model

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Example: applying that lessons

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def release_expired_numbers() do expired_numbers = TwilioService.get_expired_numbers() Enum.map(expired_numbers, fn number  case Tesla.delete(@twilio_url, ) do {:ok, %Tesla.Env{status: 204}}  TwilioService.delete_phone_number(number) _error  :error end end) end

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def release_expired_numbers() do expired_numbers = TwilioService.get_expired_numbers() Enum.map(expired_numbers, fn number  case Tesla.delete(@twilio_url, ) do {:ok, %Tesla.Env{status: 204}}  TwilioService.delete_phone_number(number) _error  :error end end) end

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def release_expired_numbers() do expired_numbers = TwilioService.get_expired_numbers() Enum.map(expired_numbers, fn number  case Tesla.delete(@twilio_url, ) do {:ok, %Tesla.Env{status: 204}}  TwilioService.delete_phone_number(number) _error  :error end end) end

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def release_expired_numbers() do expired_numbers = PhoneNumberService.get_expired_numbers() Enum.map(expired_numbers, fn number  case PhoneNumberApi.release_expired_number(number) do :ok  PhoneNumberService.delete_phone_number(number) _error  # ? end end) end

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def release_expired_numbers() do expired_numbers = PhoneNumberService.get_expired_numbers() Enum.map(expired_numbers, fn number  case PhoneNumberApi.release_expired_number(number) do :ok  PhoneNumberService.delete_phone_number(number) _error  # ? end end) end

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def release_expired_numbers() do expired_numbers = PhoneNumberService.get_expired_numbers() Enum.map(expired_numbers, fn number  case PhoneNumberApi.release_expired_number(number) do :ok  PhoneNumberService.delete_phone_number(number) _error  # ? end end) end

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def release_expired_numbers() do expired_numbers = PhoneNumberService.get_expired_numbers() Enum.map(expired_numbers, fn number  case PhoneNumberApi.release_expired_number(number) do :ok  PhoneNumberService.delete_phone_number(number) _error  # ? end end) end

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Example: selling tickets

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defmodule MyApp.Event do schema "events" do field :name, :string field :start_date, :utc_datetime field :end_date, :utc_datetime field :description, :string field :tickets_count, :integer field :price, :integer field :location, Geo.Point belongs_to :host, MyApp.User has_many :tickets, MyApp.Ticket timestamps() end end

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defmodule MyApp.Event do schema "events" do field :name, :string field :start_date, :utc_datetime field :end_date, :utc_datetime field :description, :string field :tickets_count, :integer field :price, :integer field :location, Geo.Point belongs_to :host, MyApp.User has_many :tickets, MyApp.Ticket timestamps() end end

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Single Responsibility Principle

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"The single responsibility principle (...) states that every module or class should have responsibility over a single part of the functionality provided by the software. "

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"A class should have only one reason to change."

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EventService • Finding events Responsibilities:

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EventService • Finding events • Selling tickets Responsibilities:

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EventService • Finding events • Selling tickets • Ratings Responsibilities:

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EventService • Finding events • Selling tickets • Ratings • ... Responsibilities:

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How much would it take to rewrite entire EventService from scratch?

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EventService • Finding events • Selling tickets • Ratings • ... Responsibilities:

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EventService • Finding events • Selling tickets • ... Responsibilities: RatingService

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EventService • Finding events Responsibilities: RatingService SalesService

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EventService SalesService RatingService

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Nouns vs. Verbs

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EventService SalesService RatingService "Displays events near you" "Allows users to buy tickets for events" "Allows users to give rating to the event"

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"When you think about what a service knows, you always end up back at CRUD. http:/ /www.michaelnygard.com/blog/2018/01/services-by-lifecycle/

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"When you think about what a service knows, you always end up back at CRUD. (...) Once you know what a service does, you can figure out what it needs to know. " http:/ /www.michaelnygard.com/blog/2018/01/services-by-lifecycle/

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Database becomes just an implementation detail.

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SalesService API Stable interface Hidden implementation detail

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All great, right?

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Architecture is about taking a step back, looking at a bigger picture and being aware of trade-offs when making decisions.

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Architecture is about taking a step back, looking at a bigger picture and being aware of trade-offs when making decisions.

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SalesService EventService • ticket_price • name • date • organizer { "name": "My Event", "organizer": {  }, "date": " ", "ticket_price": 200 }

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SalesService EventService • ticket_price • name • date • organizer { "name": "My Event", "organizer": {  }, "date": " ", "ticket_price": 200 }

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• Fetch both entities • Keep ticket price in both places • Keep everything only in events table • Use joins • ...

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Maintainability Performance

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Easy to understand Easy to write

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Summary

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This is hard

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‣Trade-offs everywhere ‣There's no right answer ‣There's no way to predict the future ‣A lot of attributes to optimise for ‣It's easy to over-engineer ‣Not so much resources This is hard

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‣Small pieces ‣Loose coupling ‣Strong, well-defined, stable interfaces ‣Focusing on behaviour, not data ‣Knowing common problems & patterns What helps

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Resources ‣ The art of destroying software - Greg Young ‣ Architecture the Lost Years - Robert C. Martin ‣ Modular monoliths - Simon Brown ‣ https:/ /medium.com/@dan_manges/the-modular-monolith-rails- architecture-fb1023826fc4 ‣ https:/ /m.signalvnoise.com/the-majestic-monolith-29166d022228 ‣ https:/ /medium.com/appunite-edu-collection/whats-wrong-with-a- global-user-module-ed7ed013a519 ‣ http:/ /www.michaelnygard.com/blog/2018/01/services-by- lifecycle/

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Resources

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‣ "OO" patterns (SoC, SRP, SOLID, "Tell, don't ask") ‣ Early Object Oriented ideas ‣ Microservices ‣ Domain Driven Design ‣ CQS, CQRS, Event Sourcing Extra

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Thanks! Poznan Elixir Meetup #6 mkaszubowski94