Message / Event Driven Arch

Tim Harper, Software Craftsman

Me

Books

Books

+ anything out of this

guy’s mouth

Messaging / Event Oriented Arch

Tim Harper, Software Craftsman

Why use privates in code?/** * INTERNAL API */ private[akka] object StreamLayout {

// compile-time constant final val Debug = false

final def validate(m: Module, level: Int = 0, doPrint: Boolean = false, idMap: mutable.Map[AnyRef, Int] = mutable.Map.empty): Unit = { val ids = Iterator from 1 def id(obj: AnyRef) = idMap get obj match { case Some(x) => x

Why use privates in code?/** * INTERNAL API */ private[akka] object StreamLayout {

// compile-time constant final val Debug = false

final def validate(m: Module, level: Int = 0, doPrint: Boolean = false, idMap: mutable.Map[AnyRef, Int] = mutable.Map.empty): Unit = { val ids = Iterator from 1 def id(obj: AnyRef) = idMap get obj match { case Some(x) => x

Why use privates in code?/** * INTERNAL API */ private[akka] object StreamLayout {

// compile-time constant final val Debug = false

final def validate(m: Module, level: Int = 0, doPrint: Boolean = false, idMap: mutable.Map[AnyRef, Int] = mutable.Map.empty): Unit = { val ids = Iterator from 1 def id(obj: AnyRef) = idMap get obj match { case Some(x) => x

Why use privates in code?

• Good API design

Why use privates in code?

• Good API design

• It’s easier to add functionality than remove it / change it

Why use privates in code?

• Good API design

• It’s easier to add functionality than remove it / change it

• Less guarantees = less coupling

Why use privates in code?

• Good API design

• It’s easier to add functionality than remove it / change it

• Less guarantees = less coupling

Don’t “pay the cost of a rich API without any of the benefits”

Why use privates in code?

“Private” return value?trait Publisher[T] { def subscribe(sub: Subscriber[T]): Unit } trait Subscription { def requestMore(n: Int): Unit def cancel(): Unit } trait Subscriber[T] { def onSubscribe(s: Subscription): Unit def onNext(elem: T): Unit def onError(thr: Throwable): Unit def onComplete(): Unit }

“Private” return value?trait Publisher[T] { def subscribe(sub: Subscriber[T]): Unit } trait Subscription { def requestMore(n: Int): Unit def cancel(): Unit } trait Subscriber[T] { def onSubscribe(s: Subscription): Unit def onNext(elem: T): Unit def onError(thr: Throwable): Unit def onComplete(): Unit }

“Private” return value?trait Publisher[T] { def subscribe(sub: Subscriber[T]): Unit } trait Subscription { def requestMore(n: Int): Unit def cancel(): Unit } trait Subscriber[T] { def onSubscribe(s: Subscription): Unit def onNext(elem: T): Unit def onError(thr: Throwable): Unit def onComplete(): Unit }

Private result?

Private result?• Schedule now or then

Private result?• Schedule now or then

• Run it here or there

Private result?• Schedule now or then

• Run it here or there

• Recovery, prioritization, etc.

Private result?• Schedule now or then

• Run it here or there

• Recovery, prioritization, etc.

Don’t “pay the cost of a synchronous API without any of the benefits”

Reactive Manifesto

Reactive Manifesto

Reactive Manifesto

It all starts here.

Event Oriented

• Flip the arrows

Event Oriented

Concert added to database

Event Oriented

Concert added to database

Send Email to User

Event Oriented

Concert added to database

Send Email to User

Schedule Ingestion Task

Event Oriented

Concert added to database

Send Email to User

Notify SalesForce

Schedule Ingestion Task

Event Oriented

Concert added to database

Send Email to User

Record in ElasticSearch

Notify SalesForce

Schedule Ingestion Task

Event Oriented

Concert added to database

Send Email to User

Record in ElasticSearch

Notify SalesForce

Schedule Ingestion Task

Event Oriented

Concert added to database

Send Email to User

Record in ElasticSearch

Notify SalesForce

Schedule Ingestion Task

Such knowledge

Event Oriented

Concert added to database

Send Email to User

Record in ElasticSearch

Notify SalesForce

Schedule Ingestion Task

Such knowledge

Very couple

Event Oriented

Concert added to database

Send Email to User

Record in ElasticSearch

Notify SalesForce

Schedule Ingestion Task

Such knowledge

Very couple

Wow

Event Oriented

Concert added to database

Record in ElasticSearch

Send Email to User

Schedule Ingestion Task

Notify SalesForce

Event Oriented

Concert added to database

Record in ElasticSearch

Send Email to User

Schedule Ingestion Task

Notify SalesForce

Event OrientedConcert added

to database

Record in ElasticSearch

Send Email to User

Schedule Ingestion Task

Notify SalesForce

Announce

Listen for announce

Listen for announce

Listen for announce

Listen for announce

Event Oriented

Notify SalesForce

Listen for promotion

event

Listen for new concert event

Listen for concert update

event

Functional Reactive Programming

Event X happened@ time Y

Functional Reactive Programming

Event X happened@ time Y

AS TRUE TODAY AS

WHEN IT WAS WRITTEN

Functional Reactive Programming

A @ 1:00

B @ 1:01

C @ 1:05

D @ 1:06

Functional Reactive Programming

A @ 1:00

B @ 1:01

C @ 1:05

D @ 1:06

F @ 1:00

G @ 1:01

H @ 1:05

I @ 1:06

FRPA @ 1:00

B @ 1:01

C @ 1:05

D @ 1:06

REDUCE (cache layer)

FRPA @ 1:00

B @ 1:01

C @ 1:05

D @ 1:06

REDUCE (cache layer)

It’s beginning to look

a lot like CQRS

FRP / CQRS

• “Travel through time”

• Retain all data (UPDATE = DELETE PRIOR STATE)

• Full audit log

• Separation of read / write concerns; et. al

Messaging Patterns

• Queue

• Topic

• Exchange

Orange 1

Messaging Patterns: Direct

Orange 1

Publish

“oranges”

“oranges” queue

Orange 3

Orange 2

Orange 1

Messaging Patterns: Direct

Publish

“oranges”

“oranges” queue

Orange 3

Orange 2

Orange 1

Orange 1

Messaging Patterns: Broadcast / Fanout

Orange 1

Publish

“fruit” exchange

“fruit”

Orange 3

Orange 2

“products”

Orange 3

Orange 2

Orange 1

Messaging Patterns: Broadcast / Fanout

Publish

“fruit” exchange

“fruit”

Orange 3

Orange 2

“products”

Orange 3

Orange 2

Orange 1

Orange 1

Orange 1

Messaging Patterns: Broadcast / Fanout

Publish

“fruit” exchange

“fruit”

Orange 3

Orange 2

“products”

Orange 3

Orange 2

Orange 1

Orange 1

AKA PubSub

Orange 1

Messaging Patterns: Topic / PubSub

Orange 1

Publish

“fruit” exchange topic: fruit.orange

“all-fruit” fruit.*

Apple 6

Apple 4

“apples” fruit.apples

Apple 6

Apple 4

Orange 1

Messaging Patterns: Topic / PubSub

Publish

“fruit” exchange topic: fruit.orange

“all-fruit” fruit.*

Apple 6

Apple 4

“apples” fruit.apples

Apple 6

Apple 4

Orange 1

Orange 1

Messaging Patterns: Topic / PubSub

Publish

“fruit” exchange topic: fruit.orange

“all-fruit” fruit.*

Apple 6

Apple 4

“apples” fruit.apples

Apple 6

Apple 4

Orange 1

“Yo dawgs,

this thing happened”

Message Broker Benefits

• Messages are routes and enqueued while app not booting

• Centralized point of coordination

• Replication, persistence, etc.

• If you don’t use one then you will build one.

Delivery guarantees

• At least once

• At most once

Delivery guarantees

Network Process

acksend receive

Broker

Delivery guarantees

Idempotence

• fn(fn(x)) = fn(x)

• Great idea in general

• (NOT impotency)

Idempotence

• The operation to perform is a function of the current state and next command.

Cons(in which it is acknowledged that everything has a cost)

Cons

• Complexity moved, not entirely solved.

• (although, functional discipline aids in reducing state complexity)

• Difficulty grokking message flow (DOCS!!!)

Cons

• Tracing errors can be difficult.

Cons

• Rate-limiting with high-availability can be complex.

ConsDDOS YOUR DATABASE

WITH THIS ONEWEIRD TRICK

Thanks! ( ⋂‿⋂’)

@timcharperhttp://tim.theenchanter.com/