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Events-First
Microservices
With Lagom
Gideon de Kok
@gideondk
Kenny Baas
@kenny_baas
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2
IT’S YOUR
BUSINESS. WE
ACCELERATE IT.
XEBIA GROUP CONSISTS OF SEVEN
SPECIALIZED, INTERLINKED COMPANIES
WITH OFFICES IN AMSTERDAM AND
HILVERSUM (NETHERLANDS), PARIS,
DELHI, BANGALORE AND BOSTON, WE
EMPLOY OVER 700 PEOPLE
WORLDWIDE
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Microservices
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ShipOrder
Order Shipping
REST
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ShipOrder
Order Shipping
REST
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“Any organization that designs a system will
produce a design whose structure is a copy of
the organization's communication structure.”
— Melvin Conway, 1967
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ShipOrder
Order Shipping
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Fucking Microservices
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We’re often forcing our current
problem into microservices instead
of complimenting it
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Boundaries aren’t only about form,
they’re also about communication
patterns and language
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Structure-First
Domain-Driven Design
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Structure weights you down.
Something that has been visualised
is hard to be unvisualised.
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Design is not just what it looks like
and feels like. Design is how it works.
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It is not the things that matter (in early
stages of design). It is the things that
happen
— Russ Miles
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“Event”
1. A thing that happens or takes
place, especially one of
importance.
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Events-First
Domain-Driven Design™,
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"Software development is a learning
process; working code is a side
effect."
— Alberto Brandolini
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Order
Created
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Order
Confirmed
Order
Created
Order
Paid
Order
Shipped
Order
Delivered
Order
Picked
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Order Shipping
Order
Confirmed
Order
Created
Order
Paid
Order
Shipped
Order
Delivered
Order
Picked
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package com.xebia.webshop.order.api
sealed trait OrderEvent
object OrderEvent {
case class OrderCreated(orderId: String, orderLines: Seq[OrderLine], shippingInfo: ShippingInfo)
extends OrderEvent
case class OrderConfirmed(orderId: String) extends OrderEvent
case class OrderPaid(orderId: String, orderLines: Seq[OrderLine], shippingInfo: ShippingInfo)
extends OrderEvent
object OrderCreated {
implicit val format: Format[OrderCreated] = Json.format
}
object OrderConfirmed {
implicit val format: Format[OrderConfirmed] = Json.format
}
object OrderPaid {
implicit val format: Format[OrderPaid] = Json.format
}
implicit val format: Format[OrderEvent] =
derived.flat.oformat((__ \ "type").format[String])
}
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package com.xebia.webshop.shipping.api
sealed trait OrderEvent
object OrderEvent {
case class OrderPicked(orderId: String, pickedBy: Employee) extends OrderEvent
case class OrderShipped(orderId: String, shippingReference: String) extends OrderEvent
case class OrderDelivered(orderId: String, wasDeliveredAt: LocalDateTime) extends OrderEvent
object OrderPicked {
implicit val format: Format[OrderPicked] = Json.format
}
object OrderShipped {
implicit val format: Format[OrderShipped] = Json.format
}
object OrderDelivered {
implicit val format: Format[OrderDelivered] = Json.format
}
implicit val format: Format[OrderEvent] =
derived.flat.oformat((__ \ "type").format[String])
}
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“Lagom” /lah-gome/
1. (just) right, fitting, neither too
much nor too little
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Lagom provides an opinionated
way of building microservices
that intentionally constrains what
a developer can do and how they
should do it.
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package com.xebia.webshop.order.api
import akka.NotUsed
import com.lightbend.lagom.scaladsl.api.broker.Topic
import com.lightbend.lagom.scaladsl.api.transport._
import com.lightbend.lagom.scaladsl.api.{Descriptor, Service, ServiceCall}
trait OrderService extends Service {
import Method._
import Service._
def orderEvents: Topic[OrderEvent]
final override def descriptor = {
named("order").withTopics(
topic("order-OrderEvent", orderEvents)
)
}
}
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Order
Paid
Order
Picked
Order Shipping
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Order
Paid
Order
Picked
Whenever an
Order is Paid
Order Shipping
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class OrderServicePolicy(orderService: OrderService) {
orderService.orderEvents.subscribe.atLeastOnce(Flow[api.OrderEvent].mapAsync(1) {
case x: OrderPaid => ??? // Where we should trigger our side-effect
case other => Future.successful(Done)
})
}
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package com.xebia.webshop.order.api
import akka.NotUsed
import com.lightbend.lagom.scaladsl.api.broker.Topic
import com.lightbend.lagom.scaladsl.api.transport._
import com.lightbend.lagom.scaladsl.api.{Descriptor, Service, ServiceCall}
trait OrderService extends Service {
import Method._
import Service._
def orderEvents: Topic[OrderEvent]
final override def descriptor = {
named("order").withTopics(
topic("order-OrderEvent", orderEvents)
)
}
}
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Order
Paid
Order
Picked
Whenever an
Order is Paid
Pick Order
Pay Order
Order Shipping
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Order
Order
Picked
Whenever an
Order is Paid
Pick Order
Order
Order
Paid
Pay Order
Order Shipping
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Create
Order
Order
Pay
Order
Order
Confirmed
Order
Created
Order
Paid
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Order
OrderLine
OrderLine
OrderLine
CreateOrder
Ack
OrderCreated
Akka Actor
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Order 1
Order Domain
Order 2
Order 3
Akka Singleton (Entity Framework)
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Hash(Id(Order 1)) Hash(Id(Order 2))
Hash(Id(Order 3))
A
B
C
Akka Cluster (Auto-Sharding)
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Create
Order
Order
Pay
Order
Order
Confirmed
Order
Created
Order
Paid
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trait POrderCommand
object POrderCommand {
case class CreateOrder(orderLines: Seq[POrderLine], info: PShippingInfo)
extends POrderCommand with ReplyType[Done]
case class PayOrder(reference: String) extends POrderCommand with ReplyType[Done]
case object GetOrder extends POrderCommand with ReplyType[POrder]
}
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trait POrderEvent extends AggregateEvent[POrderEvent] {
override def aggregateTag: AggregateEventTagger[POrderEvent] = POrderEvent.Tag
}
object POrderEvent {
val Tag = AggregateEventTag[POrderEvent]
case class OrderCreated(
orderLines: Seq[POrderLine],
shippingInformation: PShippingInfo) extends POrderEvent
case object OrderConfirmed extends POrderEvent
case class OrderPaid(reference: String) extends POrderEvent
}
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case class POrder(id: String, orderLines: Seq[POrderLine],
shippingInfo: Option[PShippingInfo], paymentReference: Option[String], confirmed: Boolean)
object POrder {
case class PShippingInfo(address: String, zipcode: String, city: String, country: String)
case class PSKU(id: String)
case class POrderLine(sku: PSKU, amount: Int)
}
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class OrderEntity extends PersistentEntity {
override type Command = POrderCommand
override type Event = POrderEvent
override type State = POrder
override def initialState = POrder(this.entityId, Seq.empty, None, None, false)
override def behavior: Behavior = Actions()
.onCommand[POrderCommand.CreateOrder, Done] {
case (POrderCommand.CreateOrder(orderLines, shippingInfo), ctx, state) => {
ctx.thenPersist(POrderEvent.OrderCreated(orderLines, shippingInfo)) {
evt => ctx.reply(Done)
}
}
}.onCommand[POrderCommand.PayOrder, Done] {
case (POrderCommand.PayOrder(reference), ctx, state) => {
ctx.thenPersistAll(POrderEvent.OrderPaid(reference), POrderEvent.OrderConfirmed) {
() => ctx.reply(Done)
}
}
}.onReadOnlyCommand[GetOrder.type, POrder] {
case (GetOrder, ctx, state) => ctx.reply(state)
}.onEvent {
case (POrderEvent.OrderCreated(lines, shippingInfo), state) =>
state.copy(orderLines = lines, shippingInfo = Some(shippingInfo))
case (POrderEvent.OrderPaid(reference), state) => state.copy(paymentReference = Some(reference))
case (POrderEvent.OrderConfirmed, state) => state.copy(confirmed = true)
}
}
Order
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Order
Order
Picked
Whenever an
Order is Paid
Pick Order
Order
Order
Paid
Pay Order
Order Shipping
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class OrderEntity extends PersistentEntity {
override type Command = POrderCommand
override type Event = POrderEvent
override type State = POrder
override def initialState = POrder(this.entityId, Seq.empty, None, None, false)
override def behavior: Behavior = Actions().onCommand[POrderCommand.PayOrder, Done] {
case (POrderCommand.PayOrder(reference), ctx, state) => {
ctx.thenPersistAll(POrderEvent.OrderPaid(reference), POrderEvent.OrderConfirmed) {
() => ctx.reply(Done)
}
}
}.onEvent {
case (POrderEvent.OrderPaid(reference), state) =>
state.copy(paymentReference = Some(reference))
case (POrderEvent.OrderConfirmed, state) =>
state.copy(confirmed = true)
}
}
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class OrderEntity extends PersistentEntity {
override type Command = POrderCommand
override type Event = POrderEvent
override type State = POrder
override def initialState = POrder(this.entityId, Seq.empty, None, None, false)
override def behavior: Behavior = Actions().onCommand[POrderCommand.PayOrder, Done] {
case (POrderCommand.PayOrder(reference), ctx, state) => {
ctx.thenPersistAll(POrderEvent.OrderPaid(reference), POrderEvent.OrderConfirmed) {
() => ctx.reply(Done)
}
}
}.onEvent {
case (POrderEvent.OrderPaid(reference), state) =>
state.copy(paymentReference = Some(reference))
case (POrderEvent.OrderConfirmed, state) =>
state.copy(confirmed = true)
}
}
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class OrderEntity extends PersistentEntity {
override type Command = POrderCommand
override type Event = POrderEvent
override type State = POrder
override def initialState = POrder(this.entityId, Seq.empty, None, None, false)
override def behavior: Behavior = Actions().onCommand[POrderCommand.PayOrder, Done] {
case (POrderCommand.PayOrder(reference), ctx, state) => {
ctx.thenPersistAll(POrderEvent.OrderPaid(reference), POrderEvent.OrderConfirmed) {
() => ctx.reply(Done)
}
}
}.onEvent {
case (POrderEvent.OrderPaid(reference), state) =>
state.copy(paymentReference = Some(reference))
case (POrderEvent.OrderConfirmed, state) =>
state.copy(confirmed = true)
}
}
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class OrderEntity extends PersistentEntity {
override type Command = POrderCommand
override type Event = POrderEvent
override type State = POrder
override def initialState = POrder(this.entityId, Seq.empty, None, None, false)
override def behavior: Behavior = Actions().onCommand[POrderCommand.PayOrder, Done] {
case (POrderCommand.PayOrder(reference), ctx, state) => {
ctx.thenPersistAll(POrderEvent.OrderPaid(reference), POrderEvent.OrderConfirmed) {
() => ctx.reply(Done)
}
}
}.onEvent {
case (POrderEvent.OrderPaid(reference), state) =>
state.copy(paymentReference = Some(reference))
case (POrderEvent.OrderConfirmed, state) =>
state.copy(confirmed = true)
}
}
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State
OrderPaid
OrderConfirmed
OrderUpdated
Akka Persistence
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Event Processor
OrderConfirmed
OrderPaid
OrderChanged
OrderCreated
Repository (Payment => Order)
ID: A ID: B ID: C
OrderConfirmed
OrderPaid
OrderChanged
OrderCreated
OrderConfirmed
OrderPaid
OrderChanged
OrderCreated
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Event Processor
SEQ: 12
#1
#2
#3
#4
#5
#6
#7
#8
#9
#10
#11
#12
SEQ: 0
ID: A ID: B ID: C
OrderConfirmed
OrderPaid
OrderChanged
OrderCreated
OrderConfirmed
OrderPaid
OrderChanged
OrderCreated
OrderConfirmed
OrderPaid
OrderChanged
OrderCreated
Repository (Payment => Order)
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Event Processor
SEQ: 12
#1
#2
#3
#4
#5
#6
#7
#8
#9
#10
#11
#12
SEQ: 12
ID: A ID: B ID: C
OrderConfirmed
OrderPaid
OrderChanged
OrderCreated
OrderConfirmed
OrderPaid
OrderChanged
OrderCreated
OrderConfirmed
OrderPaid
OrderChanged
OrderCreated
Repository (Payment => Order)
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package com.xebia.webshop.order.api
import akka.NotUsed
import com.lightbend.lagom.scaladsl.api.broker.Topic
import com.lightbend.lagom.scaladsl.api.transport._
import com.lightbend.lagom.scaladsl.api.{Descriptor, Service, ServiceCall}
trait OrderService extends Service {
import Method._
import Service._
def orderEvents: Topic[OrderEvent]
final override def descriptor = {
named("order").withTopics(
topic("order-OrderEvent", orderEvents)
)
}
}
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class OrderServiceImpl(persistentEntityRegistry: PersistentEntityRegistry)(implicit ec: ExecutionContext)
extends OrderService {
override def orderEvents = TopicProducer.singleStreamWithOffset { offset =>
persistentEntityRegistry.eventStream(POrderEvent.Tag, offset).filter(e =>
/* Filter some of the internal events to isolate some of the entities internal logic */
e.event == POrderEvent.OrderPaid
).mapAsync(1) { event =>
event.event match {
case x: POrderEvent.OrderPaid =>
persistentEntityRegistry.refFor[OrderEntity](event.entityId).ask(POrderCommand.GetOrder).map { x =>
val shippingInfo = x.shippingInfo.getOrElse(throw new NoShippingInfoSetException())
val message = api.OrderEvent.OrderPaid(
orderId = event.entityId,
orderLines = x.orderLines.map(x => api.Order.OrderLine(api.Order.SKU(x.sku.id), x.amount)),
shippingInfo = api.Order.ShippingInfo(shippingInfo.address, shippingInfo.zipcode, shippingInfo.country)
)
(message, event.offset)
}
}
}
}
}
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Order Shipping
Message Broker
OrderPaid
PickOrder
OrderPaid
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Order
Order
Picked
Whenever an
Order is Paid
Pick Order
Order
Order
Paid
Pay Order
Order Shipping
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Order Shipping
Message Broker
OrderPaid
PickOrder
OrderPaid
Whenever an
Order is Paid
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class OrderServicePolicy(persistentEntityRegistry: PersistentEntityRegistry,
orderService: OrderService) {
orderService.orderEvents.subscribe.atLeastOnce(Flow[OrderEvent].mapAsync(1) {
case x: OrderPaid =>
entityRef(x.orderId).ask(
PickOrder(x.orderId,
PAddress(x.shippingInfo.address, x.shippingInfo.city, x.shippingInfo.address, x.shippingInfo.zipcode)
))
case other =>
Future.successful(Done)
})
private def entityRef(orderId: UUID) =
persistentEntityRegistry.refFor[POrder](orderId.toString)
}
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Purposes are deduced from behaviour,
not from rhetoric or stated goals
— Donella H. Meadows
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Autonomy is reached by implementing
policies for behaviour instead of commanding
behaviour
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As long as events are readable on a topic,
the origin is of less importance
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Message Broker
Basket Shipping
Order
Product Stock
Legacy
Service
Gateway
Domain Events
Product
UpdateProduct
ProductUpdated / StockChanged
Anti Corruption
Layer / Data
Pumps
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Message Broker
Domain Events
Anti Corruption
Layer / Data
Pumps
API Gateway
CORE SHOPPING
Product
Event
Command
Basket
Command
Event
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Message Broker
Domain Events
Anti Corruption
Layer / Data
Pumps
API Gateway
CORE SHOPPING CHECK-OUT SELF-SERVICE
Product
Event
Payment
Command
Event
Shipping
Command
Event
Order
Command
Event
Command
Basket
Command
Event
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Event-first thinking decouples behaviour,
communication from structure
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REST as an anti-pattern
for service to service communication
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Events-first delivers on a better way of
modelling businesses in technology, while
getting the rest for “free”
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Q&A