Shaun Abram

Shaun AbramTwitter @shaunabramBlog shaunabram.comEmail shaun@abram.comLinkedIn linkedin.com/in/sabram

RESTful MicroservicesOctober 3rd, 2015

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Startup: widgets.com

MonolithDeployed as a single artifact

Scaled by replicating monolith on multiple servers

Single codebase

Adapted from http://martinfowler.com/articles/microservices.html

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Monoliths

Great.

Until they’re not.

+Tangled Dependencies…

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monoliths force everyone into the same decisions

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What is a microservice?

Small

Focused

Independent

MonolithDeployed as a single artifact

Scaled by replicating monolith on multiple servers

All functionality in a single process

MicroservicesDeployed independentlyEach functional element

as a separate serviceScaled by replicating only as needed

JavaScala

Groovy

v11 v3

v1

+ resilient

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Microservices - Not a new concept!

Unix Philosophy develop small, capable software

Do one thing well Play well with other programs Use standard interfaces

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Disadvantages of microservices

MonolithMicroservice

Operational complexity Deployment, monitoring & problem detection

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Disadvantages of microservices

MonolithMicroservice

Refactoring across service boundaries

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Disadvantages of microservices

MonolithMicroservice

Interface changes are hardMay require versioning…

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Disadvantages of microservices

MonolithMicroservice

Distributed architectures are hard!

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Microservices: better practices

Separate codebases Use monitoring Built in health checks Provide standard templates Security… Versioning…

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Microservice Security

Secure Perimeter HTTP(S) Basic Authentication Client Certificates HMAC

And beyond…

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Microservices Versioning

Backwards compatibility

Tolerant Reader and Postel's Law

Consumer-driven contracts

Semantic Versioning

Co-existing endpoints…

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Microservice versioning: coexisting endpoints

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Microservice versioning: coexisting endpoints

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Microservice versioning: coexisting endpoints

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Microservice versioning: coexisting endpoints

An example of “expand and contract”

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Microservices Versioning

Backwards compatibility

Tolerant Reader and Postel's Law

Consumer-driven contracts

Semantic Versioning

Co-existing endpoints

Co-existing servers…

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Microservice versioning: coexisting servers

- Duplicated code & fixes- Directing to the right service- Data versioning?

+ Blue Green Deployments

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Microservices or Monoliths?

Start with monoliths; Migrate slowly

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REST

Representational State Transfer

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A brief History of the WWW

HTTP URI HTML

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REST: Lessons learned

Roy Fielding

packaged the lessons learned Architectural Styles and the Design of Network-based Software

Architectures

REST

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REST

So, what is REST

Well…Theoretical vs Practical

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REST Constraints

A set of constraints. Typically with Http.

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REST Constraints

A set of constraints. Typically with Http.

1. Client Server

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REST Constraints

1. Client Server2. Stateless

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REST Constraints

1. Client Server2. Stateless3. Cache

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REST Constraints

1. Client Server2. Stateless3. Cache4. Uniform Interface

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REST Constraints

1. Client Server2. Stateless3. Cache4. Uniform Interface5. Code-On-Demand

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REST Constraints

1. Client Server2. Stateless3. Cache4. Uniform Interface5. Code-On-Demand6. Layered System

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REST

So, what is REST, really?

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REST

Resources

Uniform interfaces

Standard methods

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<soap:Envelopexmlns:soap="http://www.w3.org/2001/12/soap-envelope"soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding">

<soap:Header> <m:Trans xmlns:m="http://www.w3.com/transaction/" soap:mustUnderstand="1">234 </m:Trans></soap:Header><soap:Body xmlns:m="http://www.example.org/stock"> <m:GetStockPrice> <m:StockName>IBM</m:StockName> </m:GetStockPrice></soap:Body>

</soap:Envelope>

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myservice.com/customers/33245

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HTTP Request

GET myservice.com/customers/33245 HTTP/1.1Host: www.example.com

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Is it “RESTful” enough?

Richardson Maturity Model

Level 0 – Http tunnelling, POX, SOAP e.g. all requests to myhospital.com

Level 1 – Resources e.g. requests to hospital.com/drs/sabram

Level 2 - HTTP Verbs GET hospital.com/drs/sabram/slots

Level 3 - Hypermedia Controls

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Is it RESTful enough?

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HTTP

Idempotent

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HTTP Methods

Common GET DELETE PUT POST

Uncommon HEAD OPTIONS TRACE CONNECT

PATCH

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Rules of thumb

POST Create with the server deciding on the URI

PUT Update a resource Store the supplied entity under the supplied

URI– If exists, update; else create with that URI

PATCH Partial updates

Use you best judgment – or your corp standards!

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Uncommon HTTP Methods

HEAD Like GET but without the body Used for obtaining meta-information about the

entity Useful for testing links, e.g. for validity,

accessibility

OPTIONS Request about the capabilities of a server e.g. request a list of supported HTTP methods Possible response:

200 OK; Allow: HEAD,GET,PUT,DELETE Useful but not widely supported

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Uncommon HTTP Methods

TRACE Used to invoke a remote loop-back of the

request Plain English: Echoes back request to see what

changes have been made by intermediate servers

Often disabled for security

CONNECT For use with a proxy that can dynamically

switch to being a tunnel Typically for tunneling HTTPS through HTTP

connection

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HTTP response codes

Code Meaning Plain English(From user perspective)

1xx Informational; indicates a provisional response,e.g. 100

OK so far and client should continue with the request

2xx Successful All good3xx Redirection Something moved

4xx Client Error You messed up

5xx Server Error We messed up

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Hypermedia as the engine of application state (HATEOAS)

What is Hypermedia?

URI and URL Hypertext Multimedia Hypermedia

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Hypermedia as the engine of application state (HATEOAS)

Clients know fixed entry points to the appTransition (states) by using those links + more

If you think of Hypermedia as simply links, then HATEOAS is simply using the links you discover to navigate (or transition state) through the application.

Applies to human or software users

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Hypermedia as the engine of application state (HATEOAS)

ExampleHypermedia controls used on an album listing

<album> <name>Give Blood</name> <link rel="/artist" href="/artist/theBrakes" /> <description> Awesome, short, brutish, funny and loud. Must buy! </description> <link rel="/instantpurchase" href="/instantPurchase/1234" /></album>

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Wrapping up Microservices & REST

Microservices: A small, focused, loosely coupled service Can be developed, deployed, upgraded

independently

How to communicate with and between Microservices?REST & HTTP!

REST: Proven architectural style inspired by www Resources accessed via uniform interfaces and

HTTP Stateless

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Recommended reading

Domain Driven DesignFreeman & Pryce

Building MicroservicesSam Newman

REST in PracticeWebber, Parastatidis, Robinson

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Recommended reading

Microservices: http://martinfowler.com/articles/microservices.html

Architectural Styles and the Design of Network-based Softwarehttps://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm

Http API Design: https://github.com/interagent/http-api-design

ParallelChange (aka expand and contract): http://martinfowler.com/bliki/ParallelChange.html

Blue-Green Deployment: http://docs.pivotal.io/pivotalcf/devguide/deploy-apps/blue-green.html

Richardson Maturity Model: http://martinfowler.com/articles/richardsonMaturityModel.html

Shaun Abram

Twitter @shaunabramBlog shaunabram.comEmail shaun@abram.comLinkedIn linkedin.com/in/sabram

RESTful Microservices

Questions?