Surrounded by Microservices

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The DVD Rental Company

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Video on demand

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Original content

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Big Shift?

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Old industry !

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Remember these?

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Problem space !

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Studio apps

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Starting with a monolith

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Specialization !

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Starting fresh !

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Ruby On Rails !

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The Active Record Pattern ! Domain Objects " Business Rules # Validations $ Persistence

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Distributed data !

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Various data sources ! REST API " JSON API # GRPC $ GraphQL % Local Database

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"Data that lives in our database today might live in a service tomorrow"

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Architecture that clearly separates the business logic from any kind of implementation details and protocols

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Hexagonal Architecture

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No content

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Core concepts

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Entities

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The repositories

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The data sources

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Interactors

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Implementing business logic

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Entities module Workﬂows class ProductionEntity < BaseEntity attribute :id, AttrType::Strict::Integer attribute :title, AttrType::Strict::String attribute :logline, AttrType::Strict::String.optional end end

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dry-struct

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Entities class ProductionEntity < BaseEntity attribute :id, AttrType::Strict::Integer attribute :title, AttrType::Strict::String attribute :logline, AttrType::Strict::String.optional end

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Repositories (Custom DSL) class ProductionRepo < BaseRepo entity_class ProductionEntity def initialize(data_source: MovieProduction) super end def ﬁnd_by_id(id) wrap(data_source.ﬁnd_by_id(id)) end def search_by_title(title) wrap(data_source.search_by_title(title)) end end

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Data Sources class MovieProduction < ApplicationRecord def self.search_by_title(title) where('title LIKE ?', "#{sanitize_sql_like(title)}%") } end end

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Data Sources class MovieProductionAPI def self.search_by_title(title) SwaggerClient::MovieProductionsApi.advanced_search( search_param: title, headers: { ... }, ... ) end end

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Data Source Independent # using the default data source repo = ProductionRepo.new # swapping for a REST API data source repo = ProductionRepo.new(data_source: MovieProductionAPI)

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Interactor gem

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Interactors module Workﬂows class OnboardProduction include NetﬂixInteractor def self.call(production_id:, vertical_id:, repo: ProductionRepo.new) super end def call # validate inputs # is it okay to onboard a production? # cover edge cases # notify others about a production being onboarded end end end

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Hanami

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Implementing data sources

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API Clients

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Handwritten API Clients

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Autogenerated API Clients

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Autogenerated API Clients Swagger Code Generator GRPC JSON API Spec

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Dealing with errors

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The network is unreliable

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Graceful failure

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Logging downstream requests

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Metrics

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Error reporting

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Errors Must Be Actionable

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Avoid Alarm Fatigue

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Setting up thresholds

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Going straight to the data source

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Does it scale?

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Eventual consistency

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Consistency vs availability

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"Services should respond in a timely manner"

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What's in the future?

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Delaying decisions

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Project paradox

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The purpose of a good architecture is to delay decisions. Why? Because when we delay a decision, we have more information when it comes time to make it. - Uncle Bob

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Postgres? Cassandra? Redis? Elasticsearch?

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Testing Strategy

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The test suite must be reliable and fast

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Rails Testing

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Testing business logic

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Dependency Injection

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Testing with verified doubles describe Workflows::OnboardProduction do let(:production_id) { SecureRandom.uuid } let(:vertical_id) { SecureRandom.uuid } let(:response) do described_class.call(production_id: production_id, vertical_id: vertical_id, repo: repo) end describe 'when a production already exists' do let(:repo) { instance_double(Workflow::ProductionRepo, find_by_id: existing_production) } it 'the response is a failure' do expect(response).to be_a_failure end end ... end

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Integration specs data sources & end to end

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A fast and reliable spec suite Finished in 1 minute 2.35 seconds (ﬁles took 2.93 seconds to load) 2015 examples, 0 failures