applying domain-driven design to apis and microservices - austin api meetup

Applying Domain Driven Design to APIs and Microservices

James Higginbothamjames@launchany.com

@launchany

Great API Design is critical for product adoption and long-term

API success

API design also tells a story about your company and your vision of what the world can

become.

Your API design defines the capabilities or skills your API

offers to developers

Credit: http://kinlane.github.io/university-api-workshop/apis/

Architecture is design

API Design is an architectural concern that combines business

drivers, product design, and software design

Outside-In API Design Approach

“My data model is not my object model”– Data model is for internal storage

“My object model is not my resource model”– Resources is for external, context-based collaboration– Object model is for internal software collaboration

“My resource model is not my representation model”– There are many ways to represent resources

e.g. JSON, XML, CSV, HTML

- Mike Amundsen, API-Craft Google Group- https://groups.google.com/forum/#!search/my$20resource$20model$20is$20not/api-craft/n2Efmju5nLM/

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Applying Systems Designand Domain-Driven Design

What skills do your APIs need to offer?

Finding APIs through product and resource boundaries

Domain Driven Design (DDD)

Mapping domain concepts into software Heavy focus on domain expert involvement Common vocabulary (“Ubiquitous Language”) Boundary-driven (“Bounded Context”) Applies learning over time Based on Eric Evans' book "Domain Driven

Design”

Domain-Driven Design helps with identifying context

boundaries for complex APIs

Lack of Modularization = Regret

VS

Function-Based Module-Based

Microservice Architecture

Microservices are independently deployable, loosely-coupled components

Apply bounded context to limit cognitive load Benefit from heavy automation (CI/CD) Enable replaceability and experimentation Encourage composability of the business for

new products

Microservices require a renewed focus on

systems and API design

Modeling a System

System/Solution

Subsystem Subsystem

Module Module

Module Module

Subsystem SubsystemModule Module

LEGO as Modular System Design

System

Sub-systems

Modules

LEGO as a System of Systems

System

System

System

SystemSystem

Example: Marketplace Platform API

List Avail Inventory

DistributorAdd Product

to Order

CompleteOrder

Cancel Booking

Add Product to Inventory

Update Product Qty

LocateBooking

Redeem Booking

PointOf Sale

Remove Product

Customer

Operator

Operator

Order Mgmt

List Avail Inventory

DistributorAdd Product

to Order

CompleteOrder

Cancel Booking

Add Product to Inventory

Update Product Qty

LocateBooking

Redeem Booking

Operator

PointOf Sale

Remove Product

Customer

Operator

Inventory Mgmt

Fulfillment

Driving API Design

Each subsystem has an API that exposes one or more endpoints

Order API

List Avail Inventory

DistributorAdd Product

to Order

CompleteOrder

Cancel Booking

Add Product to Inventory

Update Product Qty

LocateBooking

Redeem Booking

PointOf Sale

Remove Product

Customer

Operator

Inventory API

Fulfillment API

Operator

Identifying product opportunities becomes easier

when we have boundaries around the APIs

Order API

List Avail Inventory

DistributorAdd Product

to Order

CompleteOrder

Cancel Booking

Add Product to Inventory

Update Product Qty

LocateBooking

Redeem Booking

Operator

Remove Product

Inventory API

Fulfillment API

#1 #2`

PointOf Sale

For every API, ask: “What resources will it offer?”

Use domain-driven design to find business entities, relations,

state transitions, and events

Order API

List Avail Inventory

Add Product to Order

CompleteOrder

Cancel Booking

Add Product to Inventory

Update Product Qty

LocateBooking

Redeem Booking

Remove Product

Inventory API

Fulfillment API

Order API

Availabilities

Orders

Products(Inventory)

Bookings

Inventory API

Fulfillment API

Same entity (Products), Conceptually different to

the API context!

Availabilities- product

- date(s) avail- qty avail

Orders- bookings

- order total

Products- name

- avail schedule

Bookings- product- date(s)- status

Availabilities- product

- date(s) avail- qty avail

availabilityChanged()

Orders- bookings

- order total

created()updated()

Products- name

- avail schedule

created()removed()updated()

Bookings- product- date(s)- status

redeemed()cancelled()

Availabilities- product

- date(s) avail- qty avail

availabilityChanged()

Orders- bookings

- order total

created()updated()

Products- name

- avail schedule

created()removed()updated()

Bookings- product- date(s)- status

redeemed()cancelled()

Order API Inventory API

Fulfillment API

Map Resources to the API

API composability using microservices

Public APIs target durability

Microservice APIs target replaceability

Availabilities Service

createAvailability()updateAvailability ()deleteAvailability ()

…availabilityChanged()

Orders ServicecreateOrder()

updateOrder ()deleteOrder ()

…created()updated()

Products ServicecreateProduct()

updateProduct ()deleteProduct ()

…created()

removed()updated()

Bookings ServicelookupBooking()

redeemBooking ()cancelBooking ()

…redeemed()cancelled()

Order API Inventory API

Fulfillment API

Orders HTTP API Inventory HTTP API

Fulfillment HTTP API

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Microservice Architecture

The Composable World of APIs

Offers API

Inventory API

Bookings API

Identity API

Accounts API

Rewards API

Partners

InternalDevelopers

Public AppDevelopers

Consumers

Third-partyApproved Apps

Summary

Great API design is critical for product adoption and long-term API success

API Design is an architectural concern that combines business drivers, product design, and software design

Systems design and DDD help with designing long-lasting APIs

Use microservices where appropriate to increase composability of your business or product

Be a storyteller using APIs

Thank you

James Higginbothamjames@launchany.com

@launchany