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![@andreasevers
Hateoas Benefit: Non-structural Changes
“customers/1/accounts/1/products/1234”
auto-discoverable through HATEOAS as
“customers[1].accounts[1].products[1234]”
will not break when 1234 as id is changed to “basementNerd”](https://image.slidesharecdn.com/microserviceshypermediaapis-javaday-160108132538/75/Microservices-with-Netflix-OSS-Hypermedia-APIs-JavaDay-Kiev-61-2048.jpg)
![@andreasevers
Hateoas Concern: Structural Changes
“customers/1/accounts/1/products/1234”
auto-discoverable through HATEOAS as
“customers[1].accounts[1].products[1234]”
could break when accounts are bypassed](https://image.slidesharecdn.com/microserviceshypermediaapis-javaday-160108132538/75/Microservices-with-Netflix-OSS-Hypermedia-APIs-JavaDay-Kiev-62-2048.jpg)
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Microservices with Netflix OSS & Hypermedia APIs - JavaDay Kiev
The document discusses microservices and hypermedia APIs, outlining benefits such as scalability and smaller code bases, while also highlighting pitfalls like operational complexity and inadequate service boundaries. It emphasizes the importance of HATEOAS (Hypermedia as the Engine of Application State) for client-server communication, which aids in discovering runtime actions and adapting to structural changes without breaking existing clients. Additionally, it critiques current API documentation practices and promotes the use of hypermedia-aware formats for better interoperability.
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Microservices with Netflix OSS & Hypermedia APIs - JavaDay Kiev
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- 2. @andreasevers WHOAMI • Work forOrdina Belgium • Open source enthusiast • Spring contributor • Speaker • Technical lead & coding architect @ Proximus • Marathon runner
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- 4. @andreasevers Benefits • Small, easyto understand code base • Easy to scale • Easy to throw away • Easy to deploy • Ability to use a different technology stack • Smaller teams • System resilience
- 5. @andreasevers Pitfalls “If you can'tbuild a monolith, what makes you think microservices are the answer?” Simon Brown
- 6. @andreasevers Pitfalls • Failing toadopt a contract-first approach • Assuming the wrong communication protocol • Introducing a shared domain model • Defining inappropriate service boundaries • Neglecting DevOps and testing concerns • Disregarding the human factor • Operational complexity not under control • Failing to embrace eventual consistency
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- 9. @andreasevers Gateway – What’sthe use? • Surgical Routing
- 10. @andreasevers • Surgical Routing • Stress Testing • Canary Testing Gateway – What’s the use?
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- 12. @andreasevers • Surgical Routing • Stress Testing • Canary Testing • Request authentication & authorization • Choosing origin servers Gateway – What’s the use?
- 13. @andreasevers • Surgical Routing • Stress Testing • Canary Testing • Request authentication & authorization • Choosing origin servers • Routing the request to an origin • Logging debug info • Adding headers to the request and response • Gathering statistics and metrics • Filter error handling • Generate static responses Gateway – What’s the use?
- 14. @andreasevers • Surgical Routing • Stress Testing • Canary Testing • Request authentication & authorization • Choosing origin servers • Routing the request to an origin • Logging debug info • Adding headers to the request and response • Gathering statistics and metrics • Filter error handling • Generate static responses • Load Shedding Gateway – What’s the use?
- 15. @andreasevers • Surgical Routing • Stress Testing • Canary Testing • Request authentication & authorization • Choosing origin servers • Routing the request to an origin • Logging debug info • Adding headers to the request and response • Gathering statistics and metrics • Filter error handling • Generate static responses • Load Shedding • Dynamic behavior change Gateway – What’s the use?
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- 19. @andreasevers Service Registry Service Registry loyalty userbilling billing’ loyalty user user origin Origin 1 Origin 2billing loyalty origin
- 20. @andreasevers Service Registry Service Registry loyalty userbilling billing’ loyalty user billing user origin Origin 1 Origin 2 loyalty origin
- 21. @andreasevers billing Service Registry Service Registry loyalty billing billing’ loyalty useruser origin loyalty origin Origin 1 user billing’ billing Origin 2
- 22. @andreasevers Service Registry Service Registry loyalty useruser origin loyalty origin Origin 1billing Origin 2 Service Registry loyalty user user origin loyalty origin Origin 1billing Origin 2 loyalty Cached Registry
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- 28. @andreasevers Circuit Breaker Gateway µS customer µS userµS loyaltyµS customer µS loyalty Backends
- 29. @andreasevers Circuit Breaker -Fallbacks
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- 31. @andreasevers Circuit Breaker -Dashboard
- 32. @andreasevers Circuit Breaker -Dashboard
- 33. @andreasevers Circuit Breaker -Dashboard
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- 43. @andreasevers Contracts & loosecoupling We can achieve this by using Hypermedia
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- 45. @andreasevers Hypermedia h8ps://vimeo.com/20781278 Sub-constraints: • IdenDficaDon of resources (URIs) • ManipulaDon via representaDons (request & response bodies) • Self-descripDve messages (headers) • Hypermedia as the engine of applicaDon state HTTP as applica+on protocol
- 46. @andreasevers Hypermedia h8ps://vimeo.com/20781278 Sub-constraints: • IdenDficaDon of resources (URIs) • ManipulaDon via representaDons (request & response bodies) • Self-descripDve messages (headers) • Hypermedia as the engine of applicaDon state If you don’t do this Then you don’t adhere to this And you are missing out on these
- 47. @andreasevers Why Hateoas? • Updatingserver-side web APIs only to learn that client applications no longer work as expected without undergoing code updates • Moving long-lived server applications to a new DNS name (e.g. from www.belgacom.be to www.proximus.be) and having to completely rewrite all of the API documentation as well as update all existing client code with all its links to the server’s APIs • Implementing new or modified process flow within the server-side application and discovering that existing clients break when encountering the new rules, ignore the rules, or, worse, continue to execute their own code in a way that creates invalid results on the server
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- 54. @andreasevers Hateoas in action Howwould you explain to a client to get to the Nerd in the Basement painting? A. Go to Amazon.com, in the categories go to fine arts, follow paintings, more specifically oil paintings, and click on the one with the title Nerd in the Basement B. Type http://www.amazon.com/Nerd-in-the-Basement/dp/ B00L849CSS/ref=lp_6685279011_1_2? s=art&ie=UTF8&qid=1431864368&sr=1-2 in your browser
- 55. @andreasevers Hateoas in action HTMLis a hypermedia format <a> is a link with method GET <form> is a link with method POST (or other if specified) The browser understands this syntax and shows a link or a form if the server response contains these tags
- 56. @andreasevers Hateoas Requirements Communication betweenClient and Server depends on: • Where does the client have to start? • Root API • In regular websites: the homepage • Where am I? • How do I interpret the current API response? • In regular websites: the syntax of HTML is interpreted by the browser • Where can I go? • What does a link or form with a certain relation or class mean? • In regular websites: link with relation “stylesheet”, form with action “login”
- 57. @andreasevers Hateoas in action Amazon.com(and any other website in the whole world wide web) applies Hateoas. Why wouldn’t your API do the same?
- 58. @andreasevers Hateoas Benefit: Runtimeaction discovery GET /account/12345 HTTP/1.1 HTTP/1.1 200 OK <?xml version="1.0"?> <account> <account_number>12345</account_number> <balance currency="usd">100.00</balance> <link rel="deposit" href="/account/12345/deposit" /> <link rel="withdraw" href="/account/12345/withdraw" /> <link rel="transfer" href="/account/12345/transfer" /> <link rel="close" href="/account/12345/close" /> </account>
- 59. @andreasevers Hateoas Benefit: Runtimeoperation discovery GET /account/12345 HTTP/1.1 HTTP/1.1 200 OK <?xml version="1.0"?> <account> <account_number>12345</account_number> <balance currency="usd">-25.00</balance> <link rel="deposit" href="/account/12345/deposit" /> </account>
- 60. @andreasevers Hateoas Concern: Scope Incase of one or two clients built in the same team, it is arguable whether auto-discoverability is really a necessity
- 61. @andreasevers Hateoas Benefit: Non-structuralChanges “customers/1/accounts/1/products/1234” auto-discoverable through HATEOAS as “customers[1].accounts[1].products[1234]” will not break when 1234 as id is changed to “basementNerd”
- 62. @andreasevers Hateoas Concern: StructuralChanges “customers/1/accounts/1/products/1234” auto-discoverable through HATEOAS as “customers[1].accounts[1].products[1234]” could break when accounts are bypassed
- 63. @andreasevers Hateoas Benefit: Changingthe URI of a resource “customers/1/accounts/1/products/1234” being returned as part as the response body of “customers/1/accounts/1” will not break the client
- 64. @andreasevers Content Types "text/html" • Browsersknow how to parse it • Browsers understand keywords inside it • E.g: a + href , form + action + method , ... "application/json" or "application/xml“ • Clients know how to parse it • Clients don’t understand keywords inside it • Needs a uniform format as communication between client & server • Needs a reference for out-of-bound (api-specific) keywords
- 65. @andreasevers Content Types • JSON • NOT hypermedia-aware by default • Needs a fixed format to support links and forms • Many formats available • XHTML • IS hypermedia-aware by default • Harder to process XHTML responses using javascript (xpath is required) • The API responses can also be read by a human as regular HTML pages • SVG, Atom, HTML • Similar as XHTML but not preferred
- 66. @andreasevers JSON Formats • JSON-LD • Augmenting existing APIs without introducing breaking changes • Needs HYDRA as a vocabulary for communicating operations • Decoupling of API serialization format & communication format • HAL • Minimal, light weight syntax and semantics • Offers most of the benefits of using a hypermedia type • Easy to convert existing API to HATEOAS • Chosen and supported by Spring • No support for specifying operations • Collection+JSON • Can list queries that your collection supports and templates that clients can use to alter your collection • Great for publishing user editable data • SIREN • Represents generic classes of items • Supports operations • Concept of classes, bringing a sense of type information to your API responses.
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- 69. @andreasevers What should youdocument Resources Links Cross-cutting concerns
- 70. @andreasevers What shouldn’t youdocument URIs
- 71. @andreasevers What does itlook like when you get it wrong?
- 72. @andreasevers What does itlook like when you get it right?
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- 77. @andreasevers Best practices fordocumentation Write as much as possible in a format which is designed for writing Don’t use the implementation to provide the documentation Provide some guarantees that the documentation is accurate h8ps://github.com/spring-projects/spring-restdocs
- 78. @andreasevers Thank you foryour attention @andreasevers https://github.com/oraj-360 http://registry.oraj360.cfapps.io/ https://netflix.github.io/ http://projects.spring.io/spring-cloud/ http://projects.spring.io/spring-hateoas/ https://github.com/spring-projects/spring-restdocs