Winter is coming - Speaker Deck

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Winter is coming Luis Zamith

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Umbrella Apps

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Application Master Elixir.IEx.Supervisor Elixir.IEx.Config OTP Applications (the IEx example)

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Application Master Elixir.IEx.Supervisor Elixir.IEx.Config Umbrella APPS Application Master Elixir.Auth.Supervisor Elixir.Auth.Repo … Application Master Elixir.Phoenix.Supervisor Elixir.Phoenix.Code Reloader.Server …

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$ mix new shelf --umbrella

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* creating .gitignore * creating README.md * creating mix.exs * creating apps * creating config * creating config/config.exs

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* creating .gitignore * creating README.md * creating mix.exs * creating apps * creating config * creating config/config.exs

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MAINTAINABLE BUILDING A APPLICATION

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Large ﬁles

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Slower Pace

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High Coupling

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Low cohesion

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Easy to UNDERSTAND CHANGE Easy to

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The system is the asset. Code is a liability. “ - Chad Fowler https://www.youtube.com/watch?v=-UKEPd2ipEk

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DOMAIN DRIVEN DESIGN

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Subdomains Sales (Supporting Subdomain) Support (Generic Subdomain)

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Sales (Supporting Subdomain) Support (Generic Subdomain) Sales Context Support Context Bounded Contexts

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Bounded Contexts

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No content

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Total unification of the domain model for a large system will not be feasible or cost-effective “ - Eric Evans Domain-Driven Design: Tackling Complexity in the Heart of Software

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Sales (Supporting Subdomain) Shipping (Supporting Subdomain) Sales Context Shipping Context Manufacturing (Core Subdomain) Manufacturing Context CRM (external)

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Sales (Supporting Subdomain) Shipping (Supporting Subdomain) Manufacturing (Core Subdomain) App Context CRM (external)

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Customer Address Product Territory Sales Person Sales Bounded Context

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Customer Address Domain Invariant There cannot be more than one customer per address Customer Aggregate Consistency and transactional boundary Aggregate Root

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Big Design Up Front

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CQRS

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CQS If you have a return value you cannot mutate state. If you mutate state your return type must be void CQRS CQS different model by responsibility +

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Client Data Command Model Query Model App create persist find read

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It is not possible to create an optimal solution for searching, reporting, and processing transactions utilizing a single model. “ - Greg Young https://cqrs.files.wordpress.com/2010/11/cqrs_documents.pdf

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Event Sourcing

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Projection (read model) Command AG (Aggregate Root) Persists  Event Publishes  Event Message Bus Reads Event Persists Data Queries Event Store Database Bounded Context A

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Umbrella Apps

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https://github.com/commanded/commanded

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Shipping.ship_order(%{…}) Sales.place_order(%{…}) %PlaceOrder{…} Router Order (Aggregate Root) %PlaceOrder{…} EventHandler %OrderPlaced{…} Sales context EventHandler %ShipOrder{…} Router Shipment (Aggregate Root) %ShipOrder{…} EventHandler %ShippedOrder{…} Shipping context EventHandler

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defmodule Sales do alias Acme.Sales.Router alias Acme.Sales.Commands.{PlaceOrder} alias Acme.Sales.Projections.{PlacedOrders} def place_order(%{total_price_cents: total_price_cents, buyer_uuid: buyer_uuid}) do uuid = UUID.uuid4() %PlaceOrder{uuid: uuid, total_price_cents: total_price_cents, buyer_uuid: buyer_uuid} |> Router.dispatch() end def list_orders do PlacedOrders.list end end Public API

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defmodule Acme.Sales.Router do alias Acme.Sales.Orders.Order alias Acme.Sales.Commands.{ PlaceOrder, } use Commanded.Commands.Router dispatch [ PlaceOrder, ], to: Order, identity: :uuid end Router

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defmodule Acme.Sales.Router do alias Acme.Sales.Orders.Order alias Acme.Sales.Commands.{ PlaceOrder, } use Commanded.Commands.Router dispatch [ PlaceOrder, ], to: Order, identity: :uuid end Router

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defmodule Acme.Sales.Orders.Order do alias Acme.Sales.Orders.Order alias Acme.Sales.Commands.{PlaceOrder} alias Acme.Events.{OrderPlaced} defstruct [:uuid, :skus, :total_price_cents, :buyer_uuid] def execute(%Order{uuid: nil}, %PlaceOrder{…}) do %OrderPlaced{…} end def apply(%Order{} = state, %OrderPlaced{…}) do %Order{state | uuid: uuid, …} end end Aggregate Root

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defmodule Acme.Sales.Projections.PlacedOrders do defmodule Handler do … use Commanded.Event.Handler, name: "sales_placed_orders", start_from: :origin def handle(%OrderPlaced{uuid: uuid} = event, _meta) do persist_order(event) :ok end end end Event Handler / Projection

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Conclusion Building maintainable apps that scale is not easy Communication with domain experts keeps the abstractions in check (aka I’m ﬁnally done) Straight-forward MVC is flawed

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Homework Think about the subdomains and bounded contexts for the app you’re currently working on and draw a diagram. Do you think it could be improved with these techniques? Bonus: Implement it with Umbrella Apps and Commanded