Presented at Houston Tech Fest 2009. Many developers use enterprise service bus (ESB) tools such as BizTalk or, for those looking at a lighter-weight approach, NServiceBus. What many fail to realize is that we have another option, one that has been tried and tested for many years and that we all use daily: HTTP. Find out how HTTP can deliver a much more maintainable, simpler solution to your ESB problems.

1. HTTP: the other ESB Ryan Riley Catapult Systems, Inc. Houston TechFest 2009

2. Agenda Setting the Stage Alternatives HTTP: the application protocol Common Concerns Questions Resources

3. Setting the Stage

4. First things first Demand – Specialized Tools Different tools needed among front and back office, as well as field workers Once people get used to a tool, they don’t want to change … except to get the features they want Supply – One-size-fits-all Create reusable frameworks or components and force them to fit the need Save time and money (80/20 rule)

5. The result? Old Computer Equipment 1 from Dolor IpsumSome rights reserved

6. The Integration Problem Start with Application Silos Then need to Share and Aggregate Data Note: Different systems with different needs Different interpretations of data semantics MUST communicate Systems rarely die, but we keep adding more

7. The Contenders File sharing Databases Direct sharing or ETL / Data Stores How do you negotiate schema changes? Message-Oriented Middleware (MOM) Fire and forget Vendors rule the world: Message Broker, ESB, etc. Service-Oriented Architecture (SOA) Back to silos Which platform: Java, .NET, ESB framework, etc.

8. Complexity becomes us Starts simple Ends … Spaghetti? Yum! from DanoSome rights reserved

9. ESB to the rescue!

10. … or perhaps not “Enterprise Spaghetti Bus” – Jim Webber

11. Meanwhile … New patterns and practices Agile and Lean TDD, BDD, DDD, CI, CQS/DDDD, etc. Frameworks and tools to the rescue! The web as an application platform WS-* emerges as an SOA solution Rails & co make web programming easier

12. Alternatives

13. WS-* Messaging: SOAP Discoverability: WSDL Security: WS-Security Reliability: WS-MessageReliability And a host of others: WS-BusinessActivity BPEL Etc.

14. WS-* (cont.) Scalability Reliance on HTTP POST Complex to achieve Transactions Complicated protocols Based on classic RPC paradigms Brought to you by HTTP POST

15. Other alternatives ESB frameworks: NServiceBus, MassTransit, Rhino.ServiceBus, etc. Back to file/database sharing? Most of these are fire and forget models.

16. HTTP: the application protocol (and you thought the second T was for transport?)

17. HTTP is comprehensive HTTP verbs GET PUT POST DELETE HEAD OPTIONS And more through extensibility!

18. Messaging Request Response It’s about communication! GET /index.html HTTP/1.1 Accept: application/xhtml+xml Accept-Language: en HTTP/1.1 200 OK Content-type: application/xhtml+xml Content-length: 16 Hello TechFest!

19. Status Codes 100 – 101 Informational 200 – 206 Success 300 – 307 Redirection 400 – 417 Client Error 500 – 505 Server Error

20. GET Idempotent = massively scalable via caching Control caching through HTTP headers: Client => Last-Modified + If-Modified-Since or If-None-Match + ETag Server => Cache-Control and Expires

21. PUT Useful for updating and creating Idempotent = safe to repeat

22. POST Create a new resource Not necessarily safe

23. DELETE Disable a resource (though not necessarily destroy) Safe to repeat, but the response is generally different when the resource doesn’t exist.

24. HEAD Retrieves only the headers Conditional GET

25. OPTIONS Retrieves the HTTP verbs a resource URI will accept. The protocol tells the client how it may proceed.

26. Hypermedia Types XHTML (application/xhtml+xml) RSS (application/rss-2.0) Atom/AtomPub (application/atom+xml) Custom (application/vnd.my-format)

27. XHTML?

28. XHTML for Messaging

29. Why not XLink? Open XML link extension Not well understood nor clearly defined In the end, you would still need custom processing, so use application/vnd.custom+xml instead of application/xml

30. Atom / AtomPub Well-understood hypermedia format Collection <atom:feed> and single <atom:entry> formats Can use <atom:link> within custom media types for well understood link semantics Works well as a queue (if you must) Simple and extensible Debate over message formats in REST

31. Add Semantics Microformats RDF / RDFa(FOAF) Prefermicroformats(rel tag)

32. The Role of Hypermedia REpresentational State Transfer (REST) Accept header(contentnegotiation) State transitions / Workflows (HATEOAS) Single entry point Next steps provided through links Can swap out providers (links) GET /index.html HTTP/1.1 Accept: application/xhtml+xml, application/json Accept-Language: en

33. HATEOAS http://www.infoq.com/articles/subbu-allamaraju-rest

34. HATEOAS, cont. No HATEOAS With HATEOAS http://www.infoq.com/articles/subbu-allamaraju-rest

35. Reliability Idempotency Response Error Codes HTTP is synchronous by nature Other ESB platforms are generally asynchronous Fire and forget Need additional fault tolerance mechanisms

36. Security HTTP Basic and Digest authentication HTTPs, the tried and true (but not cahceable) OpenID, OpenAuth, SAML

37. Scalability Stateless, so massively scalable Client and Proxy caches

38. Transactions Hypermedia (HATEOAS) Different paradigm with richer semantics Workflows and state transitions

39. How to GET a Cup of Coffee http://www.infoq.com/articles/webber-rest-workflow

40. Common Concerns

41. Security Concerns Isn’t the web inherently insecure? HTTPs is used everyday to transact millions Other protocols emerging OpenId + OpenAuth SAML

42. Complexity Few frameworks exist for pure HTTP use RESTClient and Sinatra (Ruby) Limonade (PHP) OpenRasta (.NET) Fairly simple to create from scratch Mash-ups (just see how easy this is) On the web Call services from within Excel

43. OpenRasta (C#)

44. Limonade (PHP)

45. Sinatra (Ruby)

46. Tight-coupling This is a fear from having used WSDL HATEOAS reduces coupling even more! Don’t use URI templates (except internally) URIs can be swapped at any time Requires a layer in between your domain and the external API Upgrade client and server independently (Accepts header)

47. Summary

48. There is no spoon (or bus) Paradigm shift Dumb network vs. Smart network Meaningful semantics over classic, distributed spaghetti architecture Take advantage of theexisting, richinfrastructure

49. Distributed computing for years now has seemed like an endless repackaging of the same old ideas, patterns, and technology. Through REST, I finally feel like distributing computing is evolving and moving forward again. While REST won't solve world hunger, it will certainly give us a new perspective to practice software engineering.~ Bill Burke, JBoss

50. Questions?

51. References Dr. Roy Fielding’s Dissertation HTTP/1.1 (rfc2616) The Atom Syndication Format The Atom Publishing Protocol

52. Books Get /Connected (coming 2009/2010)(Parastatidas, Robinson, Webber) RESTful Web Services(Richardson & Ruby) RESTful Web Services Cookbook(Allamaraju & Amundsen)

53. Presentations Get /Connected Guerilla SOA A Couple of Ways to Skin an Internet Scale Cat Does My Bus Look Big in This? RESTful Approaches to Financial Systems Integration