designing a serverless application with domain driven design · strategic design ddd patterns &...

Designing a Serverless Application with Domain Driven Design

Susanne KaiserIndependent Tech Consultant

@suksr

$2,840,000,000,000TWOTRILLIONEIGHTHUNDREDFOURTYBILLION USD

Costs of Poor Software Quality in the US in 2018 (by CISQ report )

Source: https://www.it-cisq.org/the-cost-of-poor-quality-software-in-the-us-a-2018-report @suksr

Some Indicators for Poor Software Quality (extracted from CISQ report )

Increasing defect trend

Low test coverage

Cyclomatic complexity

Large inheritance depthHigh amount of effort to understand piece of code

Badly engineered software

Lack of domain knowledge

Based on: https://www.it-cisq.org/the-cost-of-poor-quality-software-in-the-us-a-2018-report

Communication and coordination breakdowns in (large) teams

High degree of class coupling

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Domain Driven Design (DDD)

Business Domain Needs Strategy

Software Design

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Domain Driven Design (DDD) – TerminologyStrategic DesignTactical Design

Bounded ContextUbiquitous Language

Core SubdomainSupporting SubdomainGeneric Subdomain

Problem SpaceSolution Space

Context MapsAnti-Corruption LayerShared KernelOpen Host ServiceSeparate WaysPartnershipCustomer-SupplierConformist

Domain ModelEntity Value ObjectAggregateRepositoryFactoryApplication ServiceDomain ServiceDomain Event

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DDD & Wardley Maps

Evolution

Genesis Custom-Built Product (+rental) Commodity (+utility)

Movement

Uncharted Industrialised

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Evolution

Visualisation of a value chain’s evolution

Movement

Wardley Maps BY SIMON WARDLEY

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Wardley Maps – VALUE CHAIN

Who are your users?

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Who are your users?

What are your users’ needs?

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Who are your users?

What are your users’ needs?

What are the components/activities to fulfill your users’ needs incl. dependencies?

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Wardley Maps – LANDSCAPE

Evolution

Components alongevolution axes

Movement

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Genesis Custom-Built Product (+rental) Commodity (+utility)Evolution

Everything evolves

Past Current Future

Supply CompetitionDemand Competition

Wardley Maps – PATTERNS

Movement

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Past Current Future

Characteristics changeUncharted

Undefined marketUncertain

UnpredictableRare

Poorly understood

Forming marketLearning on use

Increasing understandingSlowly increasing

consumptionRapid increases in

learning

Growing marketLearning on operationIncreasing educationRapidly increasing

consumptionRapid increase in use

Mature marketKnown / accepted

StableWidespread and stabilising

Commonly understood(in term of use)

Industrialised

Wardley Maps – PATTERNS

Movement

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Wardley Maps – PRINCIPLES

Use appropriate methodsper evolution stage

Build in-houseUse/buy off-the-shelf product

Outsource to utility suppliers

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Wardley Maps – PRINCIPLES Build in-houseUse/buy off-the-shelf product

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Wardley Maps – PRINCIPLES Build in-house Use/buy off-the-shelf product

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Know your users &focus on user needs

Wardley Maps – PRINCIPLES Build in-house / AgileUse/buy off-the-shelf product / Lean

Outsource to utility suppliers / Six Sigma

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Domain Driven Design

Ubiquitous Language

Domain Knowledge

Understanding the problem domain firstbefore solving it

Problem Domain

Domain Experts

Development Teams

Collaboration

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DDD & Wardley Maps Problem Domain

Strategic Design

DDD Patterns & Practices

Tactical Design

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ical D

Strategic Design

Tactical Design

Analysing the business domain

Discovering Subdomains

Problem Space

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Strategic Design

Tactical Design

Problem Space

Decomposing into modular components (Bounded Contexts (BC))

Mapping interaction patterns between BC (Context Maps)

Solution Space

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ical D

Map High-Level

Design Decisions

Strategic Design

Tactical Design

Architecting a solution fitting the problem domain as closely as possible

Provides building blocks to implement domain model

Problem Space

Decomposing into modular components (Bounded Contexts (BC)

Mapping interaction patterns between BC (Context Maps)

Solution Space

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Solution Space

ical D

High-Level Design Decisions

Low-Level Design Decisions

Distilling the problemdomain & discovering the

core subdomain

DDD & Wardley Maps

Core Subdomain

Problem DomainSTRATEGIC DESIGN (PROBLEM SPACE)

Supporting Subdomain

Generic Subdomain

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core subdomain

DDD & Wardley Maps

Core Subdomain

Problem Domain

Competitive advantage ComplexChanges oftenBuild in-house

STRATEGIC DESIGN (PROBLEM SPACE) Supporting Subdomain

Generic Subdomain

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core subdomain

DDD & Wardley Maps

Core Subdomain

Problem Domain

No competitive advantage Quite simpleDoes not change oftenPrefer to buy/use off-the-shelf

Generic Subdomain

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core subdomain

DDD & Wardley Maps

Core Subdomain

Problem Domain

No competitive advantage Quite simpleDoes not change oftenPrefer to buy/use off-the-shelf

No competitive advantage Generally complexDoes not change oftenBuy/use off-the-shelf / outsource

Generic Subdomain

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Model Driven DesignDDD & Wardley MapsSTRATEGIC DESIGN (SOLUTION SPACE)

Development Teams

Domain Experts

Ubiquitous Language

Analysis Model

Code Model

Domain Model

Core Subdomain

Generic Subdomain

Problem Domain

abstracted by

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Bounded ContextsDDD & Wardley MapsSTRATEGIC DESIGN (SOLUTION SPACE)

Core Subdomain

Generic Subdomain

Problem Domain

Linguistic/semantic boundary

Ownership boundary

Model integrity boundary

Physical boundary

Different architectural patterns per context possible

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Microservice candidates

Evaluate Submissions

Manage Event

Organiser

Build & PublishSchedule

Communicate w/ Speakers

Signup/Signin

Know your users &focus on user needs

Submit Session

DDD & Wardley MapsSTRATEGIC DESIGN (PROBLEM SPACE)

Speaker

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Manage Event

Organiser

Signup/Signin

Speaker

Submit Session

DDD & Wardley MapsSTRATEGIC DESIGN (PROBLEM SPACE)

Discovering subdomains

Supporting GenericCore

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Manage Event

Organiser

Signup/Signin

Speaker

Submit Session

DDD & Wardley MapsSTRATEGIC DESIGN (SOLUTION SPACE)

Event Evaluation AccountSchedule MessageSession

Domain Models

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Manage Event

Organiser

Signup/Signin

Speaker

Submit Session

DDD & Wardley Maps

Event Evaluation AccountSchedule Message

Speaker

Session

STRATEGIC DESIGN (SOLUTION SPACE)Domain Models

@suksr

Manage Event

Organiser

Signup/Signin

Speaker

Submit Session

DDD & Wardley Maps

Event Evaluation AccountSchedule Message

Speaker Profile

Submitted Session

CfP Settings

RecipientOpen CfP Evaluated

SessionScheduled Session

STRATEGIC DESIGN (SOLUTION SPACE)Domain Models

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Manage Event

Organiser

Signup/Signin

Speaker

Submit Session

DDD & Wardley Maps

STRATEGIC DESIGN (SOLUTION SPACE)Bounded Contexts

Event Evaluation AccountSchedule MessageSubmitted Session

CfP Settings

RecipientOpen CfP Evaluated

SessionScheduled Session

Speaker Profile SessionEvaluation

SubmissionHandling

EventMngmnt.

ScheduleMngmnt.

Messaging

Account Handling

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Manage Event

Organiser

Signup/Signin

Speaker

Submit Session

DDD & Wardley Maps

STRATEGIC DESIGN (SOLUTION SPACE)

SubmissionHandling

EventMngmnt.

SessionEvaluation

Messaging Account Handling

ScheduleMngmnt.

Bounded Contexts

Ownership boundary

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Manage Event

Organiser

Signup/Signin

Speaker

Submit Session

DDD & Wardley Maps

STRATEGIC DESIGN (SOLUTION SPACE)

SubmissionHandling

EventMngmnt.

SessionEvaluation

ScheduleMngmnt.

Bounded Contexts

Ownership boundary

Physical boundary

Data store

Artefact

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Manage Event

Organiser

Signup/Signin

Speaker

Submit Session

DDD & Wardley Maps

TACTICAL DESIGN

SubmissionHandling

EventMngmnt.

SessionEvaluation

ScheduleMngmnt.

Architectural Patterns

Architectural patterns can differ per Bounded Context, e.g.

Layered Architecture

Hexagonal Architecture

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ical D

Hexagonal Architecture

Business Logic

Application

REST-API

Message Broker

Adapter

PortInnerOuter

Outside

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Manage Event

Organiser

Signup/Signin

Speaker

Submit Session

DDD & Wardley Maps

TACTICAL DESIGN

SubmissionHandling

EventMngmnt.

SessionEvaluation

ScheduleMngmnt.

Business Logic Implementation Patterns

Business logic implementation patterns can differ per Bounded Context, e.g.

Domain Model

Active Record

Transaction Script

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ical D

Manage Event

Organiser

Signup/Signin

Speaker

Submit Session

DDD & Wardley Maps

TACTICAL DESIGN

SubmissionHandling

EventMngmnt.

SessionEvaluation

ScheduleMngmnt.

Building Blocks of Domain Models

● Value Object● Entity● Aggregate● Repository● ApplicationService● Domain Event● ...

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ical D

Example Domain Model

create: Eventpublish

reschedulerename

EventIdid: string

create: Namename: string

EventStatusCREATEDACTIVATEDDEACTIVATED

delete

Description

create: Description

desc: string

Period

create: Period

start: Dateend: Date

Value Object

Entity

Aggregate Root

Aggregate

@suksrEventModel

BOUNDED CONTEXT: EVENT MANAGEMENT

FunctionEvent

Event-Driven Workflow

Hardware Data StoreO/SVirtualization Container Runtime

Fully Managed By Third Party

Ephemeral Function

Pay-per-ExecutionAuto-Scaling

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triggers

Serverless w/ FaaSCHARACTERISTICS

Lambda

API Gateway

DynamoDB

Step Functions

Core AWS Serverless Building Blocks

Kinesis

CloudWatch

Cognito

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and more

Serverless AWS BUILDING BLOCKS

Backend-API w/ Serverless

Business Logic

Application

Adapter

EventController

AWS API Gateway REST-API with AWS API-Gateway and

AWS Lambda

EventController

AWS API Gateway

newEvent deleteEvent publishEvent

POST /events

DELETE /events/{id}

POST /events/{id}/publish

InnerOuter

Outside

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(Adapter)

EventApplicationService(Port)

export class EventController {

private readonly eventService: EventApplicationService;

public constructor(eventService: EventApplicationService) { this.eventService = eventService; }

public publishEvent: Handler = async (event: APIGatewayEvent, context: Context, callback: Callback) => {

if (!event.pathParameters && !event.pathParameters.id) { return callback(null, failure({ status: "error", error: "no event id specified" })); } const eventId = new EventId(event.pathParameters.id);

await this.eventService.publishEvent(eventId); callback(null, success({ status: "ok" }));

} catch(e) { return callback(null, failure({ status: "error", error: e })); } };

public newEvent: Handler = async (event: APIGatewayEvent, context: Context, callback: Callback) => { // ... //

REST-API Adapter

LambdaFunction

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Backend-API w/ Serverless

Application

EventController

AWS API Gateway

DynamoDBEventRepository

EventApplicationService

EventRepository

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(Adapter)

(Port)

(Adapter)

Backend-API w/ ServerlessBOUNDED CONTEXT: EVENT MANAGEMENT

InnerOuter

Outside

export default class EventApplicationService {

private readonly eventRepository: EventRepository; constructor(eventRepository: EventRepository) { this.eventRepository = eventRepository; }

public async publishEvent(id: EventId): Promise<void> {

const event = await this.eventRepository.eventOfId(id);

if (!event) { throw new Error("Could not publish event with id " + id + ", since event does not exist."); }

event.publish(); await this.eventRepository.saveEvent(event); } public async newEvent(command: NewEventCommand): Promise<EventId> { // ... //

ApplicationService

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Backend-API w/ ServerlessBOUNDED CONTEXT: EVENT MANAGEMENT

Application

EventController

AWS API Gateway

EventRepository

(Adapter)

(Port)

(Adapter)

Domain ModelBC: EVENT MANAGEMENT

reschedulerename

EventIdid: string

deactivate

Description

create: Description

desc: string

Period

create: Period

Value Object

Entity

Aggregate Root

Aggregate

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InnerOuter

Outside

export default class Event {

readonly id: EventId; name: Name; description?: Description; status: EventStatus; period: Period;

private constructor(id: EventId, name: Name, status: EventStatus, period: Period, description?: Description) { this.id = id; this.name = name; this.description = description; this.status = status; this.period = period; }

public publish() { if (this.status === EventStatus.CLOSED) { throw new ValidationError("status","You cannot publish a closed event"); } if (this.status === EventStatus.PUBLISHED) { throw new ValidationError("status", "This event has already been published"); } this.status = EventStatus.PUBLISHED; }

public static create(id: EventId, name: Name, period: Period, status?: EventStatus, description?: Description): Event { // ... //}

Aggregate

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Application

EventController

AWS API Gateway

EventRepository

export default interface EventRepository {

saveEvent(event: Event): void; eventOfId(id: EventId): Promise<Event|null>; // ... //}

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(Adapter)

(Port)

(Adapter)

InnerOuter

Outside

Data Storage with AWS DynamoDB

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Application

EventController

AWS API Gateway

EventRepository

(Adapter)

(Port)

(Adapter)

InnerOuter

Outside

export default class DynamoDBEventRepository implements EventRepository {

private static TABLE_NAME: string = "events"; private readonly dynamoDbClient: AWS.DynamoDB.DocumentClient;

constructor() { this.dynamoDbClient = new AWS.DynamoDB.DocumentClient(); }

public saveEvent(event: Event) { const params : DocumentClient.PutItemInput = { TableName: DynamoDBEventRepository.TABLE_NAME, Item: { eventId: event.id.toString(), name: event.name.value, startDate: event.period.startDate.toISOString(), endDate: event.period.endDate.toISOString(), description: event.description ? event.description.value: undefined, eventStatus: event.status, cfp: event.cfp ? { description: event.cfp.description.value, startDate: event.cfp.period.startDate.toISOString(), endDate: event.cfp.period.endDate.toISOString(), id: event.cfp.id ? event.cfp.id.toString(): null }: null } };

return this.dynamoDbClient.put(params).promise(); }

public async eventOfId(id: EventId): Promise<Event|null> { // ... //}

Database Adapter

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Application

EventController

AWS API Gateway

EventRepository

(Adapter)

(Port)

(Adapter)

reschedulerename

EventIdid: string

deactivate

Description

create: Description

desc: string

Period

create: Period

Value Object

Entity

Aggregate Root

Aggregate

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InnerOuter

Outside

Manage Event

Organiser

Signup/Signin

Speaker

Submit Session

DDD & Wardley Maps

TACTICAL DESIGN

SubmissionHandling

EventMngmnt.

SessionEvaluation

ScheduleMngmnt.

DDD suits best for the core subdomain

Movement

Build in-house Use/buy off-the-shelf product

- or -- or -

@suksr

ical D

Decomposing into Modular Components

Business Domain

Needs Strategy

Better Software Design

Ubiquitous Language

Domain Knowledge

Domain Experts

Development Teams

Collaboration

Gaining Domain Knowledge

Aligning Software Design to Business Domain

Do not apply DDD everywhere!Focus on your core!

Core Subdomain

DDD helps with ...

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Core Subdomain

Discovering the Core Subdomain

Some References

https://learnwardleymapping.com/https://medium.com/wardleymapshttps://miro.com/blog/wardley-maps-whiteboard-canvas/https://github.com/wardley-maps-community/awesome-wardley-maps

Susanne KaiserIndependent Tech Consultant

@suksrsusanne@kaiser-consulting.net

designing a serverless application with domain driven design · strategic design ddd patterns &...

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