microservices with netflix oss & hypermedia apis - javaday kiev

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Microservices & Hypermedia APIs

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WHOAMI

• Work for Ordina Belgium

•  Open source enthusiast

•  Spring contributor

•  Speaker

•  Technical lead & coding architect @ Proximus

• Marathon runner

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Benefits

• Small, easy to understand code base • Easy to scale • Easy to throw away • Easy to deploy • Ability to use a different technology stack • Smaller teams • System resilience

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Pitfalls

“If you can't build a monolith, what makes you think microservices are the answer?”

Simon Brown

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Pitfalls

• Failing to adopt 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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Netflix OSS

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Gateway

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Gateway – What’s the use? •  Surgical Routing

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•  Surgical Routing •  Stress Testing •  Canary Testing

Gateway – What’s the use?

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Gateway

µS µS µS µS µS µS

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•  Surgical Routing •  Stress Testing •  Canary Testing •  Request authentication & authorization •  Choosing origin servers

Gateway – What’s the use?

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•  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?

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•  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?

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•  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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Service Registry

Service Registry

loyalty

user billing

billing’

loyalty user user origin

Origin 1

Origin 2 billing

loyalty origin

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Service Registry

Service Registry

loyalty

user billing

billing’

loyalty user

billing user origin

Origin 1

Origin 2

loyalty origin

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billing

Service Registry

Service Registry

loyalty

billing

billing’

loyalty user user origin

loyalty origin

Origin 1

user

billing’

billing Origin 2

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Service Registry

Service Registry

loyalty user user origin

loyalty origin

Origin 1 billing Origin

2

Service Registry

loyalty user user origin

loyalty origin

Origin 1 billing Origin

2

loyalty

Cached Registry

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Service Registry

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Circuit Breaker

Backend µS

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Circuit Breaker

Backend µS

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Circuit Breaker Gateway

µScustomer µSuser µSloyalty µScustomer µSloyalty

Backends

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Circuit Breaker - Fallbacks

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Circuit Breaker

Backend µS

stream

information

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Circuit Breaker - Dashboard

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Circuit Breaker - Dashboard

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Circuit Breaker - Dashboard

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Config

µScustomer

µSuser

µSloyalty

Config Server

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Metrics & Admin

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Metrics & Admin

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Metrics & Admin

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Metrics & Admin

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Metrics & Admin

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Metrics & Admin

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Metrics & Admin

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Metrics & Admin

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Contracts & loose coupling We can achieve this by using Hypermedia

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Hypermedia

Hypermedia As The Engine Of Application State

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Hypermedia

h8ps://vimeo.com/20781278

Sub-constraints:•  IdenDficaDonofresources(URIs)•  ManipulaDonviarepresentaDons(request&

responsebodies)

•  Self-descripDvemessages(headers)•  HypermediaastheengineofapplicaDonstate

HTTPasapplica+onprotocol

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Hypermedia

h8ps://vimeo.com/20781278

Sub-constraints:•  IdenDficaDonofresources(URIs)•  ManipulaDonviarepresentaDons(request&

responsebodies)

•  Self-descripDvemessages(headers)•  HypermediaastheengineofapplicaDonstate

Ifyoudon’tdothis

Thenyoudon’tadheretothis

Andyouaremissingoutonthese

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Why Hateoas?

• Updating server-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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Hateoas In Action

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Hateoas in action

How would 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

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Hateoas in action

HTML is 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

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Hateoas Requirements

Communication between Client 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”

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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?

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Hateoas Benefit: Runtime action 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>

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Hateoas Benefit: Runtime operation 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>

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Hateoas Concern: Scope

In case of one or two clients built in the same team, it is arguable whether auto-discoverability is really a necessity

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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”

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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

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Hateoas Benefit: Changing the 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

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Content Types

"text/html" •  Browsers know 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

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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

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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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Considerations

Maturity

Client implementation

Caching

Versioning

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Documentation

h8ps://speakerdeck.com/ankinson/documenDng-resTul-apis-webinar

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What should you document

Resources

Links

Cross-cutting concerns

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What shouldn’t you document

URIs

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What does it look like when you get it wrong?

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What does it look like when you get it right?

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Swagger

Doesn’t support Hypermedia

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Swagger

It’s URI centric

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Swagger

It’s leaky

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Swagger

It’s huge

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Best practices for documentation

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

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Thank you for your attention

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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