Coding Resiliently with Akka

ResilientlyCoding

Scalain AkkawithDerek Wyatt

Twitter: @derekwyattEmail: derek@derekwyatt.org

Tuesday, 4 February, 14

What’s Resiliency?

What’s Resiliency?Tolerance against faultsW

Grace in the face of insane success W

Slowing down instead of shutting downW

to the crap that happensResiliency is about reactingbecause life is, basically a problem

CCCloud Resiliency

CCCloud ResiliencyCQueues

CClustered DatabasesCVirtual Machines

CZookeeperCLoad Balancers

CCCloud ResiliencyCQueues

CClustered DatabasesCVirtual Machines

CZookeeperCLoad Balancers

Great tools. I’m going to

assume you use them.

How Akka Helps

How Akka HelpsAkka is a toolki for asynchrony5Resilient systems are asynchronous systems

Akka is buil using queues5Queues add resilient points of communication

Akka divorces threads from work5Improper use of threads kills resiliency

Akka’s Actors incorporate faul tolerance5A crash is just standard operating procedure

Akka Clusters5Clustering? Come on... Resilient

And there’s more!

Why We Don’t Code Resiliently

Why We Don’t Code Resilientlya.k.a Callback Hell1) REST request comes in2) Validate user identity3) Get profile from DB4) Grab a few pics5) Get recent Twitter activity6) Return REST response

Do it asynchronously

and don’t block

Do it asynchronously

and don’t block

Welcome to Callback Hell

Callback Hell

Callback Hellpublic void restHandler(RESTRequest req) { idService.validate(req.userInfo, new Callback(ValidateResult result) { if (result.isValid) { db.getProfile(req.userId, new Callback(UserProfile profile) { picServer.get(profile.pic1, new Callback(Pic p1) { picServer.get(profile.pic2, new Callback(Pic p2) { picServer.get(profile.pic3, new Callback(Pic p3) { picServer.get(profile.pic4, new Callback(Pic p4) { picServer.get(profile.pic5, new Callback(Pic p5) { twitterServer.getRecentActivity(req.userInfo, new Callback(TwitterActivity activity) { req.sendResponse(pic1, pic2, pic3, pic4, pic5, activity) }) }) }) }) }) }) }) })}

We didn’t handle timeouts

We didn’t handle errors

We actually didn’t make it thread safe

We did throw up a little though...

☉☉☉☉

Functional Asynchrony

Functional Asynchronyimplicit val timeout = Timeout(30.seconds)def restHandler(req: RESTRequest): Future[RESTResponse] = { val resp = for { validity <- idService.validate(req.userInfo) if validity.isValid profile <- db.getProfile(req.userId) pic1 <- picServer.get(profile.pic1) pic2 <- picServer.get(profile.pic2) pic3 <- picServer.get(profile.pic3) pic4 <- picServer.get(profile.pic4) pic5 <- picServer.get(profile.pic5) activity <- twitterServer.getRecentActivity(req.userInfo) } yield SuccessfulResponse(pic1, pic2, pic3, pic4, pic5, activity) resp.recover { e => FailedResponse(e) }}

We handle timeouts (!!)

We handle errors (!!)

It’s immutable and thread safe (!!)

We got to keep our lunch down

☉☉☉☉

The Circuit Breaker

The Circuit BreakerFor the times when you gotta fail the whale ⦿

Closed

HalfOpen

Success

Trip Breaker

Calls Failing Fast

Attempt Reset

Trip Breaker

Reset Breaker

Closed

HalfOpen

Success

Trip Breaker

Calls Failing Fast

Attempt Reset

Trip Breaker

Reset BreakerDB

Closed

HalfOpen

Success

Trip Breaker

Calls Failing Fast

Attempt Reset

Trip Breaker

Reset BreakerDB

Circuit Closed

Circuit Open

Load BalancingActors are untyped endpointsYou can easily swap one for anotherActors have dispatchersHow messages are dispatched is configurableYou can only communicate through messagesYou can route them however you like

Messages can carry the state dataActors then become completely stateless and Resilient

Scaling Up

Scaling Up⦿ It’s all about dispatchers and untyped endpoints

••

BalancingDispatcher

Client

Normally the message from the client would go to the middle Actor, but the Balancing Dispatcher lets the last one “steal” it because it can handle it faster.

Scaling Out

Scaling Out☉Routers are another way for messages to reach Actors

☉A router igures ou which Actor to send to based on rules

DBActor

Client Router DBActor

DB ClusterMachine 1

DB ClusterMachine 2

DB ClusterMachine 3

DBActor

DB ClusterMachine 1

DB ClusterMachine 2

DB ClusterMachine 3

This router can

route consistently

based on sender

DBActor

DB ClusterMachine 1

DB ClusterMachine 2

DB ClusterMachine 3

This router can

route consistently

based on sender

☉Routers can also resize the number o Actors dynamically

Clustering

⦿Akka can spawn and communicate with Actors on remote nodes

Clustering

⦿Akka can spawn and communicate with Actors on remote nodes Boring!

Clustering

⦿Akka can spawn and communicate with Actors on remote nodes Boring! (OK, that’s really cool, but...)

Clustering

⦿ You can cluster your Actors as well

Clustering

⦿Akka takes care of letting you know when nodes come and go

Clustering

⦿Akka takes care of letting you know when nodes come and go

⦿Clustering provides a ton of possibilities to design for resiliency

Persistence - Event Sourcing

Persistence - Event Sourcing⨂ Akka provides the ability to persist incoming messages

Persistence - Event Sourcing⨂ Akka provides the ability to persist incoming messages⨂ This helps for fault tolerance... DUH

Persistence - Event Sourcing⨂ Akka provides the ability to persist incoming messages⨂ This helps for fault tolerance... DUH⨂ It also provides the ability to move stateful Actors

Persistence - Event Sourcing⨂ Akka provides the ability to persist incoming messages⨂ This helps for fault tolerance... DUH⨂ It also provides the ability to move stateful Actors⨂ Or provide tools for “Crash-Only” software

ActorMessageCrash! ActorEvent 1

Event 2

Event 3

Good to go!

Being Resilient

Being Resilient☉Akka provides the foundation for resilien programming and design

Queues, Dispatchers, Async, Messages, realistic guarantees⨳

☉Then you ge...

Routers⨳Clustering⨳

Remote Deployment⨳

Persistence⨳

Resiliency Patterns⨳

Message Oriented Flexibility⨳

☉Then you ge...

Persistence⨳

☉Existing cloud components are vial for resiliency

☉Then you ge...

Persistence⨳

☉Existing cloud components are vial for resiliency

☉Akka picks up where those components leave of

Go write some Code

http://akka.iohttp://github.com/akka/akka

http://scala-lang.orghttp://github.com/scala/scala

Get Scala

Get AkkaDerek Wyatt

Twitter: @derekwyattEmail: derek@derekwyatt.org

Coding Resiliently with Akka

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