The document discusses the importance of effective API design, emphasizing that it serves as a contract with consumers and must focus on capability offerings. It introduces Domain-Driven Design (DDD) as a method for identifying context boundaries in APIs, promoting high cohesion and loose coupling within a microservices architecture. Additionally, it provides practical steps for migrating to microservices, highlighting the need for clear interfaces and automated deployment pipelines.

1. Applying Domain Driven Design to
APIs and Microservices
James Higginbotham
@launchany

2. Your API tells a story and
creates a conversa3on between
you and the world

5. A great API design strategy is
cri3cal for API product adop3on
and sustainable applica3on
development

7. Your API design is a contract
with your API consumers. It is
“mission cri3cal” to them.

9. Your API design is composed of
the capabili3es (or “skills”)
you offer to developers

10. API Skills == “I want to…”

11. What skills do your
APIs need to offer?

12. Outside-In API Design Approach
Web
Applica3on
API Design – “The Contract”
Internal
Applica3on
API Consumer
Mobile
Applica3on

13. API Design is an architectural
concern that combines business,
product design, and soKware
engineering

15. Lack of ModularizaIon = Regret
VS
Purpose-Based Module-Based

16. High cohesion
internally for
closely-related
funcIonality
Loose coupling
externally across
modules without
internal details
High Cohesion + Loose Coupling

17. package package
public
Public APIs
encourage
loose coupling
between modules
API
Scoping rules
restrict access
outside of modules
X
API-Centric SoPware Design

18. Systems Design
System
Subsystem Subsystem
Module Module
Module Module
Subsystem Subsystem
Module Module

19. LEGO as Modular System Design
System
Subsystems
Modules

20. API
API
API
System/SoluIon
Subsystem Subsystem
Subsystem
Module Module
Module Module
Module Module
Module Module
Module Module
Module Module
Module Module
Module Module

21. Domain-Driven Design helps
with iden3fying context
boundaries for complex APIs

22. Domain Driven Design (DDD)
u Maps domain concepts into soPware
u Heavy domain expert involvement
u Common vocabulary (“Ubiquitous Language”)
u Boundary-driven (“Bounded Context”)
u Apply learning over Ime

25. “I need to mul3ply two numbers
together. So, I am building
a microservice architecture.”
- almost everyone today

26. Microservice Architecture
u Loosely-coupled, service-oriented architecture
u Apply bounded context to limit cogniIve load
u Independently deployable via automaIon
u Enable replaceability and experimentaIon
u Encourage composability of the business
u Best for large teams, or co-located disparate data

27. Applying Systems Design
and Domain-Driven Design
to find API boundaries
and resources

29. List Avail
Inventory
Distributor
Add Product
to Order
Complete
Order
Cancel
Booking
Add Product
to Inventory
Update
Product Qty
Locate
Booking
Redeem
Booking
Point
Of Sale
Remove
Product
Customer
Operator
Operator

30. Order Mgmt
List Avail
Inventory
Distributor
Add Product
to Order
Complete
Order
Cancel
Booking
Add Product
to Inventory
Update
Product Qty
Locate
Booking
Redeem
Booking
Operator
Point
Of Sale
Remove
Product
Customer
Operator
Inventory Mgmt
Fulfillment

31. Each subsystem has an API that
exposes one or more endpoints

32. Order API
List Avail
Inventory
Distributor
Add Product
to Order
Complete
Order
Cancel
Booking
Add Product
to Inventory
Update
Product Qty
Locate
Booking
Redeem
Booking
Point
Of Sale
Remove
Product
Customer
Operator
Inventory API
Fulfillment API
Operator

33. Iden3fying product opportuni3es
becomes easier when we have
boundaries around the APIs

34. Order API
List Avail
Inventory
Distributor
Add Product
to Order
Complete
Order
Cancel
Booking
Add Product
to Inventory
Update
Product Qty
Locate
Booking
Redeem
Booking
Operator
Remove
Product
Inventory API
Fulfillment API
#1 #2
`
Point
Of Sale

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

36. Use domain-driven design to
find business en33es, rela3ons,
state transi3ons, and events

37. Order API
List Avail
Inventory
Add Product
to Order
Complete
Order
Cancel
Booking
Add Product
to Inventory
Update
Product Qty
Locate
Booking
Redeem
Booking
Remove
Product
Inventory API
Fulfillment API

38. Order API
Product
AvailabiliIes
Orders
Product
Inventory
Bookings
Inventory API
Fulfillment API
Same enIty (Products),
Conceptually different to
the API context!

39. Availabili3es
- product
- date(s) avail
- qty avail
Orders
- bookings
- order total
Products
- name
- avail schedule
Bookings
- product
- date(s)
- status

40. Availabili3es
- 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()

41. Availabili3es
- 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

42. Map Resources to the API

43. API composability using
microservices

44. Public APIs target durability
through external contracts
Microservice APIs target
evoluIon through
experimentaIon Photo Credit: h,ps://www.flickr.com/photos/libel_vox

45. Availabili3es Service
Orders Service
Products Service
Bookings Service
Orders HTTP API
Inventory HTTP API
Fulfillment HTTP API

46. Availabili3es Service
Orders Service
Products Service
Bookings Service
Orders HTTP API
Inventory HTTP API
Fulfillment HTTP API
Payment Service
Refund Service

47. Alexa
Voice Skill
API
Gateway
API
Gateway
Messaging
…
Microservice
…
API
…
Microservice
…
API
…
Microservice
…
API
…
Microservice
…
API
Slack
Chatbot
Web +
Mobile App
API
Gateway
Microservice Architecture

48. MigraIng to Microservices
1. Use API Facades to define clear interfaces
2. Separate complex concerns into separate
services
3. Use Service Object Paeern to decompose
4. Build an automated deployment pipeline
5. Migrate service objects to microservices

49. The Composable World of APIs
Offers API
Inventory
API
Bookings
API
Identity API
Accounts
API
Rewards
API
Partners
Internal
Developers
Public App
Developers
Consumers
Third-party
Approved Apps

50. Thank you
James Higginbotham
@launchany
hep://bit.ly/api-skills