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Spring Cloud Contract And Your Microservice Architecture

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Consumer driven contracts (CDC) are like TDD applied to the API. It’s especially important in the world of microservices. Since it’s driven by consumers, it’s much more user friendly. Of course microservices are really cool, but most people do not take into consideration plenty of potential obstacles that should be tackled. Then instead of frequent, fully automated deploys via a delivery pipeline, you might end up in an asylum due to frequent mental breakdowns caused by production disasters. We will write a system using the CDC approach together with Spring Boot, Spring Cloud Contract verifier. I'll show you how easy it is to write applications that have a consumer driven API and that will allow a developer to speed up the time of writing his better quality software.

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Spring Cloud Contract And Your Microservice Architecture

  1. 1. Consumer Driven Contracts and Your Microservice Architecture Marcin Grzejszczak, Pivotal @mgrzejszczak
  2. 2. Spring Cloud developer at Spring Cloud (Pivotal) Working mostly on Spring Cloud Sleuth and Spring Cloud Contract Automation freak About me Twitter: @mgrzejszczak Blog: http://toomuchcoding.com
  3. 3. Introduction Demo Summary Agenda
  4. 4. ● Producer ○ service that exposes an API ● Consumer ○ service that consumes the API of the producer ● Contract ○ agreement between producer and consumer how the API will look like ● Consumer Driven Contracts ○ approach where the consumer drives the changes of the API of the producer Introduction
  5. 5. ● Stub validity & reusability in the integration tests ● Nice API creation Introduction What problems are we trying to solve?
  6. 6. Introduction Typical situation HTTP CONSUMER PRODUCER
  7. 7. Introduction How to write a test for it? HTTP CONSUMER PRODUCER
  8. 8. Introduction Stub validity & reusability WE’RE ON THE CONSUMER SIDE!! CONSUMER OWNS THE STUB DEFINITIONS
  9. 9. Introduction Stub validity & reusability
  10. 10. Introduction Stub validity & reusability 10
  11. 11. Introduction Stub validity & reusability 11
  12. 12. Introduction Stub validity & reusability 12
  13. 13. Introduction Stub validity & reusability 13
  14. 14. ● My tests fail cause I’m shooting a request at a non existant URL ● I rewrote all my code to work with the new URL ● The unit and integration tests pass ● Now we deploy to an environment where real integrations will take place... Introduction So now what?
  15. 15. Introduction Ooops...
  16. 16. Stubs that were used in the build phase have nothing to do with the real API!! Introduction What went wrong? HTTP CONSUMER PRODUCER TEST OK HTTP CONSUMER PRODUCER REALITY WAT?!
  17. 17. ● Stubs reside with the consumer ● Consumer controls the stubbing process ● How are you sure that the stubs are valid? ● What if other teams want to reuse those stubs? Introduction Stub validity & reusability
  18. 18. ● It’s the consumer that uses the API ● Consumers should take part in the creation of the API of the producer ● The producer’s API change should be driven by consumers Introduction Nice API creation
  19. 19. Introduction Nice API creation - no cooperation results
  20. 20. Introduction Nice API creation - no cooperation results
  21. 21. Demo Potential answer Spring Cloud Contract
  22. 22. ● Consumer ○ service that gets beer requests ○ has to ask another service if the client can get the beer ● Producer ○ service that checks if the client is old enough to buy beer ● Feature ○ if the user is too young - the beer will not be sold ○ otherwise the beer will be granted Demo What are we going to code?
  23. 23. Introduction What are we going to code? I’m 22 give me a beer CONSUMER PRODUCER There you go! Can he get the beer? Yes!
  24. 24. Introduction What are we going to code? I’m 17 give me a beer CONSUMER PRODUCER Get lost! Can he get the beer? No!
  25. 25. Introduction What are we going to code? BLACK TERMINAL BLACK IDE CONSUMER WHITE TERMINAL WHITE IDE PRODUCER
  26. 26. Demo DEMO
  27. 27. Summary Consumer’s offline work Consumer Phase 1 Consumer Phase 2 Consumer’s switching to online Producer phase Producer’s implementing the feature
  28. 28. Summary Consumer flow 1 • starts TDD - writes the test for the feature • clones producer code to change the API locally • in the cloned producer code converts contracts into stubs and installs them locally • in the consumer code turns Stub Runner to offline mode • configures Stub Runner to download stubs of the producer • red - green - refactor on the API and tests • repeats the process until the tests are green and API acceptable • files a PR to the producer with the contract proposal
  29. 29. Summary Producer flow • takes over the PR • writes the missing implementation that will make the autogenerated tests pass • merges PR and deploys the JARs with the app and the stubs
  30. 30. Summary Consumer flow 2 • switches off the Stub Runner’s offline mode once the producer uploads the stubs • configure Stub Runner by providing the URL to a repo with stubs • will have its test broken if the producer makes any breaking changes of the API
  31. 31. With Spring Cloud Contract and Consumer Driven Contracts: ● we’ve created an API that suits the consumer and the producer ● expectations were defined by readable contracts ● expectations were tested against the producer ● producer stubs can be reused by consumers ● starting and setting stubs is fully automated Summary
  32. 32. Why use Spring Cloud Contract Verifier? ● Possibility to do CDC with messaging ● Clear and easy to use, statically typed DSL ● Automatic generation of tests from the defined Contract ● Stub Runner functionality - the stubs are automatically downloaded at runtime from Nexus / Artifactory ● Spring Cloud integration - no discovery service is needed for integration tests ● Integration with Cloud Foundry - Stub Runner Boot ● Possibility to keep all contracts in a single repo Summary
  33. 33. Demo
  34. 34. Spring Cloud Contract repo Spring Cloud Contract documentation Spring Cloud Contract Gitter Producer sample Client sample LINKS
  35. 35. Thank you! Marcin Grzejszczak Pivotal mgrzejszczak@pivotal.io mgrzejszczak

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