Microservices and the Art of Taming the Dependency Hell Monster
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The document discusses the challenges of managing dependencies in microservices, particularly the 'dependency hell' phenomenon, which occurs when software packages depend on specific versions of other packages. It emphasizes the importance of first-class API design, backward and forward compatibility, accurate documentation, and generated client libraries to mitigate these issues. Additionally, it highlights practices like semantic versioning and the use of tools like apidoc to streamline API development and maintain quality in microservice architectures.
![user-service client lib
createUser(form: UserForm): Future[User]
getUser(guid: UUID): Future[Option[User]]
deactivateUser(guid: UUID): Future[Unit]
updateUser(guid: UUID, form: UserUpdateForm):
Future[Unit]
authenticate(email: String, password: String):
Future[Boolean]
…](https://image.slidesharecdn.com/untitled-150721195347-lva1-app6892/85/Microservices-and-the-Art-of-Taming-the-Dependency-Hell-Monster-16-320.jpg)
![catalog-service client lib
getProduct(id: Long): Option[Product]
getProductsInSale(saleId: Long, limit: Int,
offset: Int): List[Product]
getSkusForProduct(productId: Long): List[Sku]
…](https://image.slidesharecdn.com/untitled-150721195347-lva1-app6892/85/Microservices-and-the-Art-of-Taming-the-Dependency-Hell-Monster-18-320.jpg)
![Example: apidoc
{
"name": “user-service",
"models": {
"user": {
"fields": [
{ "name": "id", "type": "uuid" },
{ "name": "email", "type": "string" }
]
}
}
}](https://image.slidesharecdn.com/untitled-150721195347-lva1-app6892/85/Microservices-and-the-Art-of-Taming-the-Dependency-Hell-Monster-34-320.jpg)
![apidoc Ruby Client
client = MyService::Client.new("http://localhost:8000")
organizations = client.organizations.get(:limit => 10, :offset => 0)
organizations.each do |org|
puts "Org %s is named %s" % [org.id, org.name]
end
neworg = client.organizations.post(:name => "My org")
puts "Created new org named %s" % neworg.name](https://image.slidesharecdn.com/untitled-150721195347-lva1-app6892/85/Microservices-and-the-Art-of-Taming-the-Dependency-Hell-Monster-45-320.jpg)
Microservices and the Art of Taming the Dependency Hell Monster
- 1. Microservices and the art of taming the Dependency Hell Monster Michael Bryzek Cofounder & ex-CTO Gilt @mbryzek [email protected]
- 2. InfoQ.com: News & Community Site • 750,000 unique visitors/month • Published in 4 languages (English, Chinese, Japanese and Brazilian Portuguese) • Post content from our QCon conferences • News 15-20 / week • Articles 3-4 / week • Presentations (videos) 12-15 / week • Interviews 2-3 / week • Books 1 / month Watch the video with slide synchronization on InfoQ.com! http://www.infoq.com/presentations /microservices-dependencies
- 3. Presented at QCon New York www.qconnewyork.com Purpose of QCon - to empower software development by facilitating the spread of knowledge and innovation Strategy - practitioner-driven conference designed for YOU: influencers of change and innovation in your teams - speakers and topics driving the evolution and innovation - connecting and catalyzing the influencers and innovators Highlights - attended by more than 12,000 delegates since 2007 - held in 9 cities worldwide
- 4. Dependency Hell • What is it and how does it happen? • How do we mitigate? • API design must be First Class • Backward and Forward Compatibility • Accurate Documentation • Generated client libraries
- 5. http://en.wikipedia.org/wiki/Dependency_hell Dependency hell is a colloquial term for the frustration of some software users who have installed software packages which have dependencies on specific versions of other software packages.
- 6. Example service a depends on lib-foo version 1.7 service b depends on lib-foo version 1.6 Build pulls in version 1.7. At runtime, turns out there was a breaking change in lib- foo that the compiler could not verify. Long chains of dependencies make this hard: service a depends on lib-foo depends on lib-bar depends on lib-baz http://en.wikipedia.org/wiki/Dependency_hell
- 10. 0 to 150+ People in Tech
- 11. How do you manage dependencies? And specifically those dependencies in the libraries we use.
- 12. Let’s Build an App
- 14. The Basics • User registration and login • Product catalog • Inventory data • Cart
- 15. user-service • API to create a user; fetch user details • High throughput: 10k RPS+ • Millions of users
- 16. user-service client lib createUser(form: UserForm): Future[User] getUser(guid: UUID): Future[Option[User]] deactivateUser(guid: UUID): Future[Unit] updateUser(guid: UUID, form: UserUpdateForm): Future[Unit] authenticate(email: String, password: String): Future[Boolean] …
- 17. catalog-service • API to fetch rich product details • Moderate throughput: 5k RPS+ • Millions of products
- 18. catalog-service client lib getProduct(id: Long): Option[Product] getProductsInSale(saleId: Long, limit: Int, offset: Int): List[Product] getSkusForProduct(productId: Long): List[Sku] …
- 19. inventory-service • API to check stock of individual products • High throughput: 10k RPS+ • Guarantee never oversold
- 20. inventory-service client lib numberAvailable(id: Long): Long reserve(id: Long): Token clearReservation(token: Token) lock(reservationToken: Token, externalId: UUID) …
- 21. cart-service • API to add/remove to a shopping cart • Integrates with checkout • Low throughput
- 22. cart-service client lib addToCart(id: String, skuId: Long) getCart(id: String): Cart clearCart(id: String) addToUserCart(userGuid: UUID, skuId: Long) getUserCart(userGuid: UUID): Cart clearUserCart(userGuid: UUID) …
- 23. Service Year of Latest Update Client Dependencies Futures? Example Methods user 2015 Scala 2.11, Ning 1.9 Yes createUser, deactivate catalog 2013 Scala 2.10, Ning 1.7 No createProduct inventory 2009 Java 6, Netty HTTP client. No reserve, lock cart 2008 Java 6, Apache HTTP Client. No addToCart
- 24. Then We Add Features • Loyalty • Recommendation • Account Credits • Nav bar with context, related sales • Tracking • and dozens more…
- 25. And with micro service architectures, significant new features often lead to new services and new libraries.
- 27. What happens next? • Builds get larger and slower • Create new client libraries that are each just a little bit different • Produce custom APIs that reduce interoperability • Increase amount of boilerplate code • Reduce code quality; slow down development • And Eventually you will see a production error
- 29. Minimizing the Pain • API design must be First Class • Backward and Forward Compatibility • Accurate Documentation • Generated client libraries
- 30. Guiding Principle: The Open Source Way • How do applications integrate with each other? • How do you use a library? • How much and what kind of documentation? • How do I get support / contribute / report bugs? • Public or Private is a detail
- 31. Tooling Matters • www.apidoc.me codifies these practices • very simple to get use • zero dependencies on existing software process nor runtime • Open source and free SAAS: https://github.com/mbryzek/ apidoc • First commit April 6, 2014. • Over 100 services already built at Gilt w/ apidoc
- 32. API Design Must be First Class • Protobufs, thrift, avro, swagger 2.0, and apidoc • The design of your API and the data structures themselves are the hardest things to change • Design them up front - and integrate these artifacts into your design process.
- 33. Example: AVRO idl @namespace("mynamespace") protocol User { record Employee { string email; } }
- 34. Example: apidoc { "name": “user-service", "models": { "user": { "fields": [ { "name": "id", "type": "uuid" }, { "name": "email", "type": "string" } ] } } }
- 35. “Schema First Design” Really the most important concept
- 36. Accurate Documentation • What services exist? Think of how github helps us discover what libraries and applications exist. • API as first class allows us to use these artifacts directly in our software - ensures accuracy • Semantic Versioning (http://semver.org/)
- 39. Backward Compatibility • Imagine storing all historical records • General guidelines: • New fields are either optional or have defaults • Can’t rename; Introduce new models where necessary and migration path
- 40. Forward Compatibility • Imagine new messages arrive with new data • Additional considerations: • Careful of enums; consider what happens when you add a value in the future • Careful with processing data (e.g. throwing an exception if an unknown field shows up)
- 41. Forward Compatible Enum sealed trait OriginalType object OriginalType { case object ApiJson extends OriginalType { override def toString = "api_json" } /** * UNDEFINED captures values that are sent either in error or * that were added by the server after this library was * generated. We want to make it easy and obvious for users of * this library to handle this case gracefully. * * We use all CAPS for the variable name to avoid collisions * with the camel cased values above. */ case class UNDEFINED(override val toString: String) extends OriginalType ... }
- 42. Knowing When Things Change
- 43. Generating Client Libraries • Potentially controversial; I was skeptical at first, but works • Enables consistent naming • Minimal external dependencies • Challenge: Can you generate a client that developers love?
- 45. apidoc Ruby Client client = MyService::Client.new("http://localhost:8000") organizations = client.organizations.get(:limit => 10, :offset => 0) organizations.each do |org| puts "Org %s is named %s" % [org.id, org.name] end neworg = client.organizations.post(:name => "My org") puts "Created new org named %s" % neworg.name
- 46. apidoc Scala Client val client = new com.bryzek.apidoc.api.v0.Client("http://localhost") val organizations = client.organizations.get(limit = 10, offset = 0) organizations.foreach { org => println(s"Org ${org.name} is named ${org.id}") } val neworg = client.organizations.post(name = "My org") println(s"Created new org named ${neworg.name}")
- 47. Consistency Really Matters Original Consistent Naming based on REST createUser POST /users/ Users.post createProduct POST /products/ Products.post reserve POST /reservations/ Reservations.post addToCart POST /carts/:id/products/:productId Products.postByIdAndProductId(id, productId, …)
- 48. Summary: Mitigate Dependency Hell • API design must be First Class • Backward and Forward Compatibility • Accurate Documentation • Generated client libraries
- 50. Watch the video with slide synchronization on InfoQ.com! http://www.infoq.com/presentations/ microservices-dependencies