Designing APIs and Microservices Using Domain-Driven Design
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Presented at GlueCon 2016. Applying good software engineering practices, system design, and domain-driven design for your public APIs and microservices
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Designing APIs and Microservices Using Domain-Driven Design
- 1. Applying Domain Driven Design to APIs and Microservices James Higginbotham @launchany
- 2. Your API tells a story about your company and your vision
- 6. A great API design strategy is critical for API product adoption and sustainable application development
- 8. Your APIs may not be considered “mission critical” like Stripe. But your API design is a contract with your API consumers.
- 10. Your API design is composed of the capabilities (or “skills”) you offer to developers
- 11. API Skills == “I want to…”
- 12. What skills do your APIs need to offer?
- 13. Outside-In API Design Approach Web Application API Design – “The Contract” Internal Application API Consumer Mobile Application
- 14. API Design is an architectural concern that combines business, product design, and software engineering
- 16. Lack of Modularization = Regret VS Function-Based Module-Based
- 17. High cohesion internally for common functionality Loose coupling externally across modules High Cohesion + Loose Coupling
- 18. Public APIs encourage loose coupling between modules API Scoping rules restrict access outside of modules X API-Centric Software Design
- 19. Systems Design System Subsystem Subsystem Module Module Module Module Subsystem Subsystem Module Module
- 20. LEGO as Modular System Design System Sub-systems Modules
- 21. API API API System/Solution Subsystem Subsystem Subsystem Module Module Module Module Module Module Module Module Module Module Module Module Module Module Module Module
- 22. Domain-Driven Design helps with identifying context boundaries for complex APIs
- 23. Domain Driven Design (DDD) Maps domain concepts into software Heavy domain expert involvement Common vocabulary (“Ubiquitous Language”) Boundary-driven (“Bounded Context”) Applies learning over time
- 24. “I need to multiply two numbers together. So, I am building a microservice architecture.” - almost everyone today
- 25. Microservice Architecture Loosely-coupled, service-oriented architecture Apply bounded context to limit cognitive load Independently deployable via automation Enable replaceability and experimentation Encourage composability of the business Best for larger teams
- 26. Applying Systems Design and Domain-Driven Design to find API boundaries and resources
- 28. 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
- 29. 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
- 30. Each subsystem has an API that exposes one or more endpoints
- 31. 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
- 32. Identifying product opportunities becomes easier when we have boundaries around the APIs
- 33. 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
- 34. For every API, ask: “What resources will it offer?”
- 35. Use domain-driven design to find business entities, relations, state transitions, and events
- 36. 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
- 37. Order API Product Availabilities Orders Product Inventory Bookings Inventory API Fulfillment API Same entity (Products), Conceptually different to the API context!
- 38. Availabilities - product - date(s) avail - qty avail Orders - bookings - order total Products - name - avail schedule Bookings - product - date(s) - status
- 39. 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()
- 40. 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
- 41. Map Resources to the API
- 43. Public APIs target durability through external contracts. Microservice APIs target evolution through learning and experimentation
- 44. Availabilities Service Orders Service Products Service Bookings Service Orders HTTP API Inventory HTTP API Fulfillment HTTP API
- 45. Availabilities Service Orders Service Products Service Bookings Service Orders HTTP API Inventory HTTP API Fulfillment HTTP API Payment Service Refund Service
- 47. 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
Editor's Notes
- We’re going to talk about how to design LONG-LASTING APIs. The goal is to avoid a redesign not long after your API is deployed. API TRAINING to help coach teams on how to think in APIs and apply the techniques I’ll show you today Across every team and company, I reiterate one common theme…
- Capital One is changing the way we interact with banking and bank-level security Released 3 APIs during SXSW in March
- Watson is changing the way we UNDERSTAND DATA LANGUAGE, SPEECH, VISION, and DATA INSIGHTS
- Marvel is changing the way we INTERACT with the ENTERTAINMENT MEDIA and their storytelling Characters, stories, comics, creators, and events
- At their core, APIs are contracts for software component interaction. How we design our APIs will drive the level of short and long-term success. As an example, STRIPE…
- Stripe is well known because they focus on great API design and documentation. But it extends beyond that. They tell a story with their API: “we power commerce for businesses of all sizes” Everything is built around that…
- You may not be at Stripe’s scale or mission critical for customers How you version your API design over time is important, however – IT IS A CONTRACT
- Medhi recently tweeted that Stripe maintains 50 (actually now closer to 65) different versions of their API. They OWN VERSIONING, rather than pushing it to the CONSUMER. Even when we, as designers, MISS THE MARK, we should OWN IT
- Kin Lane has been conducting API workshops at universities by showing how to ACCOMPLISH THINGS Zapier/IFTTT is his model for teaching the use of APIs
- Our DATABASES are not our API Our CODE (classes, functions) are not our API Our API is a contract that is implemented by our code and databases We must put ourselves IN THE PLACE OF THE CONSUMER, NOT THE DEVELOPER
- Web APIs are an architectural concern, but MORE THAN THAT – PRODUCT AND BUSINESS TODAY IS HTTP, TOMORROW may be something else Use architectural design techniques to drive your API design What is it we are trying to solve and how are we planning to solve it? THAT IS THE PRODUCT SIDE and WHAT IS MOST EXCITING TO ME
- <<ADV…>>There are several popular web frameworks that make building a monolithic application easy – almost trivial. These frameworks commonly offer: accelerated development, but left off modular design This leads to a lack of proper modularization, impacting our API designs
- 10 years, new frameworks, but they assume a single subsystem – the webapp or “site” They missed the mark for larger applications, trying to avoid SOA This is leading to “MONOLITHIC REGRET” and a lack of modular applications Microservices is becoming a common way to deal with this problem at LARGER SCALES
- High Cohension – common functionality that is related BELONG TOGETHER Loose coupling – reduced dependencies across modules - minimize cohesion across modules
- Public APIs define the contract that the top module is offering to other modules around it. If the API contract changes, either through a change in the inputs, outputs, or overall behavior, it can break the integration between these modules. To prevent other modules from interacting with the internal components of itself, we apply scoping rules to restrict access
- Systems: This is a completely independent system that provides a solution to one or more problems Subsystems: Bounded concerns that help to compose the system itself. Subsystems do not offer a solution on their own, but contribute a bounded portion of it. finally, Modules: These are the building blocks for composing subsystems. Modules may contain one or more components, where components are classes in object-oriented programming languages or functions in functional programming languages.
- Demonstration of LEGO of how to BREAK a big KIT (problem) into smaller, manageable modules ALIGN OURSELVES based on core competencies
- APIs provide the opportunity to connect subsystems, with internal APIs that connect modules together. We should ONLY KNOW what the subsystem APIs are, NOT THE MODULE APIs
- Approach on software development for complex needs Based on Eric Evans' book "Domain Driven Design”
- Adrian Cockcroft’s definition
- I want to SHARE what METHODS I have USED to HELP TEAMS DESIGN APIs Product development = opportunity + need + solution Systems design defines how your product is architected API Systems design tells 2 stories: about how your API is architected (internal-facing), and how your API works within other solutions (external-facing)
- Ecommerce example – what does it take to place an order? These are the skills that our API must offer Essential step #1
- First step – list, understand what the business requirements were, how different parties were to interact with the system
- Group related activities participant(s) need to perform into subsystems Use the boundaries to determine: - what has already been built in-house - what needs to be built in-house - what can be replaced by COTS, third-party APIs
- We found 2 stories: a distributor story and an operator story = 2 PRODUCTS Operators vs Distributors drove API DESIGN, DOCS, MARKETING Different vocabularies for distributors and operators
- Not “what are your endpoints” or “what are your URLs”
- Discuss aggregates, entities, and value objects. Aggregates become resources, named after the root entity within Goal: Consistent naming that reflects the API’s intended use
- PRODUCT INVENTORY PRODUCT AVAIL + ORDERS BOOKINGS
- EVENTS – often the MOST MISSED OPPORTUNITY Callbacks change the way developers interact with you API, from POLLING to automatic NOTIFICATION when things change. Allows them to be more reactive to change in your own subsystems Github callbacks expanded the development pipeline beyond a single tool vendor
- [recall early in the talk: when is my product ready to launch?] Our architecture shows us not only what we need to build, but what each party needs to accomplish their goals/solution. This helps us with product roadmaps, scheduling, and other internal aspects of product management.
- Durability == LONG LASTING Replaceability == AGILITY, EXPERIMENTATION, EVOLUTION
- Start with services for each root-level domain entity Use SERVICE OBJECTS or MICROSERVICES
- Starting with the simplest services, we can break services out as we dig into the implementation details. In this case, PAYMENT and REFUND can be broken out and assigned to a different team
- API Gateways offer public contracts, integrate with microservices
- We live in a world with a growing number of APIs Many APIs represented in this room and at this conference Let’s look for skills and capabilities around us, build APIs, and HELP OTHERS TELL A STORY