Modeling Microservices

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MODELING MICROSERVICES
Sander Hoogendoorn
ditisagile.nl
Mentoring ▪ Consulting ▪ Training ▪ Agile ▪ Software architecture ▪ Code

MICROSERVICES? STAIRWAY TO HEAVEN OR HIGHWAY TO HELL?
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Sander Hoogendoorn
Me
 Dad
 Mentor, trainer, software architect, programmer
 Books and +250 articles
 Keynotes and talks at +150 conferences
Work
 Owner ditisagile.nl
 CTO Klaverblad Insurances
Web
 www.sanderhoogendoorn.com
 www.smartusecase.com
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 @aahoogendoorn
 sander@ditisagile.nl

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MONOLITHS
Hard to deliver, even harder to test and impossible to maintain

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WHOOFYOUHASASYSTEMTHATISTOOBIG
ANDTHATYOUWOULDRATHERBREAKUP?

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Monoliths
Advantages
 A single (layered) architecture
 A single technology stack
 A single code base maintained by multiple teams
Disadvantages
 All parts are interconnected
 Many other systems are connected to your system
 Hard to change, hard to maintain
 Long time between releases, thereby increasing risks
 Slow innovation
 Hard to move to newer technologies
 Doesn’t scale very well
Product Account
Order Customer
Products Accounts
Orders Customers

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Dependencies will kill you

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A BRIEF HISTORY
OF COMPONENTS AND SERVICES

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Client server

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Component based development

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Service oriented architecture

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Microservices

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MICROSERVICES
Beyond the hype?

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Microservices. Beyond the hype?

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Gartner hype cycle

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MICROSERVICES
The clear benefits

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BUTFIRST…ADEFINITION

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Inshort,themicroservicearchitecturalstyleisanapproachtodevelopingasingleapplicationasasuiteofsmallservices,
eachrunninginitsownprocessandcommunicatingwithlightweightmechanisms,oftenanHTTPresourceAPI.
Theseservicesarebuiltaroundbusinesscapabilitiesandindependentlydeployablebyfullyautomateddeploymentmachinery.
Thereisabareminimumofcentralizedmanagementoftheseservices,whichmaybewrittenindifferentprogramminglanguages
andusedifferentdatastoragetechnologies.
MartinFowler

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Monoliths. Scalability
Product Account
Order Customer
Product Account
Order Customer
Product Account
Order Customer

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Microservices. Scalability
Product Account
OrderCustomer

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Microservices. Scalability
Product Account
OrderCustomer
Product
CustomerCustomer Customer
Account Account

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Microservices. Scalability & containers
Product Account
Order
Product
Customer
Account Account
CustomerCustomer

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Monoliths. Persistence
Product Account
Order Customer
Products Accounts
Orders Customers

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Microservices. Polyglot persistence
Product Account OrderCustomer
MongoDB
Customers
MongoDB
Orders
ActiveDirectory
Accounts
Oracle
Products

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Microservices. Promises
 Products not projects
 Scalable
 Decentralized governance
 Replaceable parts
 High performance
 Technology independent
 Polyglot persistence
 Easy to build
 Easy to test
 Easier deployment than monoliths
Product
Account
Order
Customer

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Microservices. But…
 What is a microservice exactly?
 How small is a microservice?
 Requirements in a microservice world
 Components or services
 Who owns a microservice?
 What technologies do you use?
 What protocols do you apply?
 How to define messages
 How to test microservices
 How to coordinate when business services run
across components?
 How to build deployment pipelines?
Product
Account
Order
Customer

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Opinions, opinions, opinions

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ARE MICROSERVICES
A STAIRWAY TO HEAVEN?

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OR A HIGHWAY TO HELL?

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A REAL WORLD CASE

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A major insurance company

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A major insurance company
We have
 Most functionality on an expensive mainframe
 A wide variety of large systems written in Java that are hard
to maintain and to test, and that are very hard to replace
 Individual systems that cover large areas of functionality,
usually coupled to departments
 Aging technology
 No mobile strategy, allowing for new business or new
services to clients, and intermediaries
We need to
 Get rid of the mainframe
 Shorten time-to-market
 Lower TCO
 Uphold a fully secure systems landscape

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Where do we come from?

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Outsourcing didn’t work

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Where do we go?

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FORTHETHINGSWEHAVETOLEARN
BEFOREWECANDOTHEM,
WELEARNBYDOINGTHEM
Aristotle

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MICROSERVICESREQUIREANEVOLUTIONARYARCHITECTURE

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START WITH SOME GUIDING PRINCIPLES

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Questions, questions, questions
Communicationarchitecture.Theglue
Howdowedefineinterfacesbetweenappsandcomponent?Howdowearrangemessaging?
Howdowegluetogetherrapidlychangingappsandcomponent?
Applicationarchitecture
EnduserfacingDifferentusers,differentfastevolvingneeds
Whichtechnologyisthebestforwhichpurpose?
Componentarchitecture
Componentsandservicesareevolvingrapidly.Howdowedecidewhichcomponentsweneed?
Howdowedealwithversioning?Howdowedealwithdistributedprocessesandtransactions?

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Case. Guiding principles
We decided to go from here
 Client thinks in business processes, so we implement
business processes
 We move away from the mainframe, to a new systems
landscape, consisting of micro-applications and micro-
components
 Requirements and documentation are modeled rather than
written
 Applications implement a single (elementary) business
process
 Components serve a single purpose and offer services
 Applications and components all have their own bounded
context – a domain model
 Applications and components will have an similar internal
software architecture to facilitate ease of maintenance and
allow for harvesting re-use
 Communication between applications and components will
use a simple open protocol - REST

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Presentation
Process
Domain
Services
Outsideworld
Pages
Grids/Panels,Controls
Usecases
Flow
Domainobjects,Factories/Repositories
Enums/Valueobjects/Tupels/Referenceobjects
Servicegateways,Serviceclients
Infoobjects/Searchobjects
ComponentsRelations Dossiers Intermediaries Accounts Rates

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Serviceinterface
Process
Domain
Data/Services
Outsideworld
Resources
Representations
Usecases
Flow
Storagegateways,Storageclients
StorageRelations Dossiers Intermediaries DB2 MongoDB

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NOWWHATDOESALLTHISHAVETODOWITHMODELING?

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DOINGBIGUP-FRONTDESIGNISDUMB
DOINGNODESIGNISEVENDUMBER
DaveThomas

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BUSINESS PROCESSES FIRST

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Different levels of processes (and requirements)

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A high-level business process
Step1 Step2 Step3 Step4 Step5

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Split into work processes
Step3.1 Step3.2 Step3.3 Step3.4
Step3

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Split into elementary processes - OTOPOP
Step3.3.1 Step3.3.2 Step3.3.3 Step3.3.4
Step3.3
Step3.3.5

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Smart use cases
Modeling applications
 Each elementary process is implemented in a
single application
 The requirements are modeled using smart use
cases
 Each application consists of a single sea-level use
case and a number of fish-level use cases
 Additionally we add the services that are required
to implement the applications to the model
 Doing so, we can easily do impact mapping on our
services
 Also, the smart use cases form a strong
foundation for integration testing

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Different levels of use cases
Traditional
use cases
Smart
use cases
Format Textual Visual
Granularity Different Unified
Estimate Hard Easy
Unit of work Lousy Good
Reuse Incidental Normal
Traceability Possible Normal
Testability Poor Good

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Smart use cases

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57Smart use cases

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Wireframes with use cases

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MODULAR DESIGN /
DESIGNING MICROSERVICES

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Single responsibility principle (SRP)
SOLID
 Single Responsibility Principle
 Open Closed Principle
 Liskov Substituion Principle
 Interface Segregation Principle
 Dependency Inversion Principle
Single Responsibility Principle
 Every module should have responsibility over a single part of the
functionality provided by the software,
 That responsibility should be entirely encapsulated by the class
 All its services should be narrowly aligned with that responsibility
Therefore
 Group together things that change together
 Separate things that change for different reason

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Bounded context
Domain driven design
 The paradigm of designing software based on models
of the underlying domain
 The domain model helps the business and the
developers to reason about the functionality
 A model needs to be unified – internally consistent
without contradictions
Bounded context
 The bounded context is a central pattern in domain
driven design
 When you model larger domains, it becomes
progressively harder to create this single unified model
 So, instead of creating a single unified model, you
create several, all valid within their bounded context

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The single unified domain model
Product
Vendor
Stock
Order
Client
Delivery
Payment

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Bounded contexts
Product
Vendor
Stock
Order
Client
Delivery
Payment
Product

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Bounded contexts
Modeling
 Modeled in a (single) domain model
 Model contains entities, domain objects
 Usually evolves around a single main entity (aggregate root)
Services
 Interrogate the bounded context
 Resources usually follow the aggregate root
 Services post and put representations
 Representations are mapped to the bounded context
Validation
 Representations can be validated before being mapped
 Bounded context can be validated as a whole e.g. before storing
 Business rules
 Properties and property types
Product
Vendor
Stock

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Properties and property types
Basic types
 string, integer, date, datetime
 Include nullable wrapping
Enumerations
 Set up at design time, unchangeable at run-time
 Genders, Categories
Value objects
 No specific instances
 Isbn, Email, Url, Money
References (code tables)
 Changeable at run-time, such as contract types
Associations
 To cached entities such as Country, Nationality
 To first level citizens such as Customer, Product

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66
Every application,
worker and
component
has its own
bounded context

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AND THE REST IS
COMMUNICATION (OVER HTTP)

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HTTPRETURNCODESCHEATSHEET
1**.Holdon
2**.Hereyougo
3**.Goaway
4**.Youfuckedup
5**.Ifuckedup

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HTTP GET
GET
 Retrieve whatever information is
identified by the request URI in the form
of an entity
 The entity is usually a single or a list of
objects (of the type provided by the
service, often JSON, or XML)
 GET is safe (retrieval only) and
idempotent
 Unfortunately there are many ways of
creating GET requests (see examples
below)
 Returns 200 (found), possibly 400 (bad
request) or 404 (not found)
Examples
 Get an entire collection
localhost:8080/countries
 Find objects in the collection
localhost:8080/countries?name=“stan”
 Find an object in the collection by ID
localhost:8080/countries/38
 Find a sub-object in the collection by ID
localhost:8080/countries/38/capital
 Find object in the collection by ISO
localhost:8080/countries?isocode=“GRC”
localhost:8080/countries/isocode/GRC
localhost:8080/countries/GRC

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HTTP POST
POST
 Request that the server accepts the
entity enclosed in the request as a new
subordinate of the resource identified by
the request URI
 The posted entity is subordinate to that
URI in the same way that a file is
subordinate to a directory containing it
 Returns the location header for the new
resource, possibly with created entity in
the body
 Returns 201 (created), possibly 500
(server error)
Examples
 Post to the collection (with entity in body)
localhost:8080/countries
 Returning location header

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HTTP PUT
PUT
 Requests that the enclosed entity is
stored under the supplied request URI
 If the request URI refers to an existing
resource, the enclosed entity is an
modified version of the resource
 POST identifies the resource that will
handle the enclosed entity
 PUT identifies the entity enclosed with
the request
 Returns 200 or 204 (when resource is
modified), possibly 201 (if a resource is
created), possibly 500 (server error)
Examples
 Put with ID (with entity in body)
 Update capital (with entity in body)
localhost:8080/countries/38/capital

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HTTP DELETE
DELETE
 Requests that the resource identified by
the request URI is deleted.
 Returns 200 or 204 (when resource is
deleted), possibly 500 (server error)
Examples
 Delete

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MODELING RESOURCES

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Modeling resources
Root resources (component)
/qa
/questionnaires
GET
Questionnaire
Id,Name,Description
/qa
GET the collection, but only limited to this
representation (but with locations likely)
/qa/questionnaires
/questionnaires
GET
/{id}
Questionnaire
Id,Name,Description
Question
Type,Name,Description
Answer
Name,Value
GET a single item from the collection, but
with representation
/qa/questionnaires/334532

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75
Resource
model

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76
Service
use cases

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77Component bounded context

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TESTING MICROSERVICES

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A service development lifecycle
Code DeveloperTest Test IntegrationTest AcceptanceTest LivePrepare&Design

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What to test
Developers
Unittests
Developers
Q&A
Testers
Scenario’s&API’s
Testers
Productowner
Product

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Even though you might have brilliant testers

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… please automate your tests
Developers
Unittests
Developers
Q&A
Testers
Testers
Productowner
Product

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Developer Q&A Sonarqube

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Developer Q&A Sonar

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Presentation
Process
Domain
Services
Outsideworld
Pages
Grids/Panels,Controls
Usecases
Flow
Servicegateways,Serviceclients
ComponentsRelations Dossiers Intermediaries Accounts Rates
Integrationtests
BDD&Selenium
Unittests
Unittests
Unittests

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Serviceinterface
Process
Domain
Data/Services
Outsideworld
Resources
Representations
Usecases
Flow
Storagegateways,Storageclients
StorageRelations Dossiers Intermediaries DB2 MongoDB
Integrationtests
UsingBDD
Unittests
Unittests
Unittests

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WHATABOUTBEINGINDEPENDENTLYDEPLOYABLE?

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DEPLOYING MICROSERVICES
Continuous integration, build pipelines and continuous delivery

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A typical build pipeline

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ProductionAcceptanceIntegrationTestDevelopment
A typical build pipeline

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Build pipelines in Jenkins

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Microservices. Building a deployment pipeline
Code DeveloperTest Test AcceptanceTest Acceptance Live

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Microservices. Pipeline hell?
Codev.2 DeveloperTestv.2 Testv.2 AcceptanceTestv.2 Acceptancev.2
Testv.2 AcceptanceTestv.2 Acceptancev.2 Livev.2
DeveloperTest Test AcceptanceTest Acceptance Live
Codev.3 DeveloperTestv.3
Live
Codev.2

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Dealing with breaking changes
Customer
v1
App1 App2
Customer
v1
App1 App2
v2
Customer
v1
App1 App2
v2
Customer
App1 App2
v2

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DO WE REALLY NEED PROJECTS?
From projects to releases to continuous delivery

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Do we really need projects?

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Planning?

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Or roadmap?

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Minimal viable product

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Maintenance
From projects to continuous delivery?
Project
MaintenanceMVP
MaintenanceContinuousdelivery

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Moving towards DevOps is not easy

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WORDLYWISDOMTEACHESUSTHATITISBETTERFORREPUTATION
TOFAILCONVENTIONALLYTHANTOSUCCEEDUNCONVENTIONALLY
JohnMaynardKeynes

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SOME LAST THOUGHTS

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Microservices are not for everyone
Whatarewegoingto benefit
fromthemost?
Polyglotpersistence?
Beingableto
multiplestacks?
Independently
deployable?
Enforce
modulardesign?
Continuous
Delivery?

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Minimal viable product

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ALLOW THE TEAM TO LEARN
CONTINUOUSLY…

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Will it work?

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The hockey stick model

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… AND HAVE FUN

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THIS IS
AGILE
www.createspace.com/4747266
Password: agilescrum
Discount code: KGNWKKWG

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sander@ditisagile.nl
@aahoogendoorn
REFERENCES
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Modeling Microservices

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