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5 Anti-Patterns in Api Design - buildstuff

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This talks elaborates on the Client-Server tenet of REST which focuses on separation of concerns between the client and the server. In the first third of the talk, I will talk about what the ideal client and servers are and examples of how their responsibilities. I will touch on how the word Server has lost its meaning of "serving" and the client has been overshadowed by the focus to the API. I will also compare the API to a restaurant and how its menu is the API's REST resources.

In the rest of the talk, I look at some important anti-patterns commonly seen in the industry (each with at least one example):

1) Chauvinist Server: designing the API from server's perspective failing to hide its complexity behind its API (API designed from the server's perspective)
2) Demanding client: client enforcing its special need onto the signature of the API (certain client's limitation becomes server's default behaviour)
3) Transparent Server: server exposing its internal implementation to its clients (server's underlying or private domain bleeds into the public API)
4) Presumptuous Client: The client assuming the role of a server and engage in taking responsibilities that cannot guarantee
5) Assuming Server: Server that assumes the responsibility of tailoring the response based on what it assumes client is (e.g. browser sniffing)

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5 Anti-Patterns in Api Design - buildstuff

  1. 1. API DESIGN 5 Anti-Patterns in Ali @aliostad Kheyrollahi
  2. 2. API The Art of Presentation
  3. 3. API Iceberg “This huge mass underneath the water that you can't see, the private API, is the biggest part of the whole opportunity.” Daniel Jacobson, Netflix - 2011
  4. 4. Micro services “ … the microservice architectural style is an approach to developing a single application as a suite of small services, each running in its own process and communicating with lightweight mechanisms, often an HTTP resource API” Martin Fowler - Bliki
  5. 5. REST Stateless
  6. 6. @aliostad REST Layered Architecture
  7. 7. REST Caching
  8. 8. @aliostad Resources and representations REST Uniform Interface S e l f - d e s c r i p t i v e messages Hypermedia
  9. 9. @aliostad REST Client-Server
  10. 10. @aliostad HTTP Client-Server Server Concern: e.g. returning the resource when requested with a different casing /car/123 vs /Car/123 Client Concern: e.g. Handling 301 (moved permanently) Mixed Concern: e.g. Most HTTP concepts such as Content Negotiation or Caching/Concurrency
  11. 11. @aliostad Client-Server Boundary Boundary
  12. 12. @aliostad CSDS Client-Server Domain Separation “ Client and server must define and live within their own bounded context ”
  13. 13. @aliostad CSDS Client-Server Domain Separation S e r v e r
  14. 14. API Restaurant
  15. 15. @aliostad CSDS Client-Server Domain Separation C l i e n t Can be a server itself1 2 Uses services of server(s) to bring value to end-user (directly or indirectly) 3 Free to take dependency on of Server’s public domain (URI, exchange domain) Normally keeps state but does not master it4
  16. 16. @aliostad Client-Server Boundary Boundary
  17. 17. @aliostad
  18. 18. @aliostad Anti-Pattern Transparent Server 1
  19. 19. @aliostad “server exposes its internal implementation to its clients” Anti-Pattern Transparent Server server's private domain or the domain of its underlying dependencies bleeds into its public API
  20. 20. E x a m p l e 1 Anti-Pattern Transparent Server
  21. 21. @aliostad E x a m p l e 2 Always for a customer1 2 Only for customers currently shopping 3 Get expired after inactivity A couple of tables or a document database 4 Max one basket per customer Anti-Pattern Transparent Server
  22. 22. @aliostad E x a m p l e 2 POST /baskets?cid=908 201 Created Location: /baskets/123435455456 POST /baskets/123435455456 {...}200 OK x Anti-Pattern Transparent Server
  23. 23. @aliostad E x a m p l e 2 POST customer/me/basket {…} 200 OK ✓ Anti-Pattern Transparent Server
  24. 24. @aliostad Anti-Pattern Chauvinist Server 2
  25. 25. @aliostad “designing the API from server's perspective” Anti-Pattern Chauvinist Server Server pushes its thinking and process to the client resulting in the client becoming a subordinate
  26. 26. @aliostad Anti-Pattern Chauvinist Server H A T E O A S(and not hypermedia itself) Hypermedia as the Engine of Application (state)
  27. 27. @aliostad Anti-Pattern Chauvinist Server H A T E O A S Client most likely a server wasteful to navigate2 3 Client uses more than one server 6 Microservices: servers smaller, containing a couple of resources 4 Undefined caching directives for hypermedia Server hasn’t got a clue what the application is1 5 Don’t try to spare the client composing URLs
  28. 28. @aliostad Anti-Pattern Chauvinist Server H A T E O A S?
  29. 29. @aliostad Anti-Pattern Demanding Client 3
  30. 30. @aliostad “client enforces its special needs onto the API signature” Anti-Pattern Demanding Client certain clients limitations (or reluctance to implement) become server's default behaviour
  31. 31. @aliostad E x a m p l e s Anti-Pattern Demanding Client Client enforces use of query string over HTTP headers1 2 Client pushes for consistency of parameter names with other [external] APIs 3 Client pushes for consistency of behaviour with other [external] APIs 4 Client asks for simpler model since does not need the extra data
  32. 32. @aliostad Anti-Pattern Assuming Server 4
  33. 33. @aliostad “server assumes the role of defining client experience” Anti-Pattern Assuming Server server makes decisions on issues that are inherently client concerns
  34. 34. @aliostad E x a m p l e 1 Anti-Pattern Assuming Server GET /api/catalogue/products/pages/1 GET /api/catalogue/products/pages/2 x
  35. 35. @aliostad E x a m p l e 1 Anti-Pattern Assuming Server GET /api/catalogue/products?from=1&count=30 ✓
  36. 36. @aliostad E x a m p l e 2 Anti-Pattern Assuming Server B r o w s e r s n i f f i n g
  37. 37. @aliostad Anti-Pattern Presumptuous Client 5
  38. 38. @aliostad “client takes on responsibilities that cannot fulfil” Anti-Pattern Presumptuous Client Client presumes it can fulfil some responsibilities that are inherently server’s
  39. 39. @aliostad E x a m p l e s Client implements an algorithm that needs to be centralised on server1 2 Client act as an authority for authentication or authorisation 3 Client takes control of cache invalidation Anti-Pattern Presumptuous Client
  40. 40. @aliostad Microservices take importance of APIs to a new level1 2 Think of your API as a restaurant and remember the contrast 3 Transparent Server: Exposing internals Re Cap 4 Chauvinist Server: Client becoming a subordinate 5 Demanding Client: Client enforcing special needs to API signature 6 Assuming Server: Server deciding client experience 7 Presumptuous Client: Client taking responsibilities cannot fulfil
  41. 41. Thank You @aliostad http://byterot.blogspot.com

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