Events-First Microservices with Lagom

Even with microservices starting to become a commodity, a lot of implementations still fail as microliths. To ensure the autonomy of services and its development process, strong coupling between services should be limited as much as possible. The way to achieve this is to isolate the inner working of a service at cost and to switch from a commanding and synchronous to a promising and asynchronous way of communication between services.

A route to success is to stop architectural design from a perspective of services with well-defined and canonical relationships and to switch to a model which is based on the production of immutable domain events. Not only does this way of architecting ensure a better match with the things that happen within your business. The focus on the timeline of facts over the structures producing them ensures far less coupling within your system.

In this talk, I will share how Lagom embraces this way of thinking by pushing events-first development as a default. From the event-sourcing principles within aggregates to the message-broker functionality between services, I’ll give you the background of the elements which are in place to shift your system to an event-driven microservice architecture.

Transcript

1. Events-First Microservices With Lagom Gideon de Kok @gideondk Kenny Baas @kenny_baas
2. 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
3. Microservices
4. We’re often forcing our current problem into microservices instead of complimenting it
6. ShipOrder Order Shipping
7. ShipOrder Order Shipping
8. “Any organization that designs a system will produce a design whose structure is a copy of the organization's communication structure.”
 
 — Melvin Conway, 1967
10. Order Team Shipping Team ShipOrder Order Shipping
13. Boundaries aren’t only about form, they’re also about communication patterns and language
15. We not only need boundaries, We need an architectural pattern which enable autonomy within and over those boundaries
17. Structuring business processes into domains, and aligning those with technology Domain Driven Design
18. An explicit boundary for language, complexity, logic, context Bounded Contexts
19. Structure-First Domain-Driven Design
20. Structure weights you down. Something that has been visualised is hard to be unvisualised.
21. Design is not just what it looks like and feels like. Design is how it works.
22. It is not the things that matter (in early stages of design). It is the things that happen — Russ Miles
23. “Event”
 1. A thing that happens or takes place, especially one of importance.
24. Events-First Domain-Driven Design™,
25. "Software development is a learning process; working code is a side effect." — Alberto Brandolini
34. Order Created
35. Order Confirmed Order Created Order Paid Order Shipped Order Delivered Order Picked
36. Order Shipping Order Confirmed Order Created Order Paid Order Shipped Order Delivered Order Picked
37. 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]) }
38. 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]) }
39. “Lagom” /lah-gome/ 1. (just) right, fitting, neither too much nor too little
40. Lagom provides an opinionated way of building microservices that intentionally constrains what a developer can do and how they should do it.
41. 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) ) } }
42. Order Paid Order Picked Order Shipping
43. Order Paid Order Picked Whenever an Order is Paid Order Shipping
44. 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) }) }
45. 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) ) } }
46. Order Paid Order Picked Whenever an Order is Paid Pick Order Pay Order Order Shipping
47. Order Order Picked Whenever an Order is Paid Pick Order Order Order Paid Pay Order Order Shipping
48. Create Order Order Add Payment Information Order Confirmed Order Created Order Paid
49. Order OrderLine OrderLine OrderLine CreateOrder Ack OrderCreated Akka Actor
50. State OrderPaid OrderConfirmed OrderUpdated Akka Persistence
51. Order 1 Order Domain Order 2 Order 3 Akka Singleton (Entity Framework)
52. Hash(Id(Order 1)) Hash(Id(Order 2)) Hash(Id(Order 3)) A B C Akka Cluster (Auto-Sharding)
53. Create Order Order Pay Order Order Confirmed Order Created Order Paid
54. 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] }
55. 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 }
56. 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) }
57. 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) } }
58. 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) } }
59. 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) } }
60. 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) } }
61. Event Processor OrderConfirmed OrderPaid OrderChanged OrderCreated Repository (Payment => Order) ID: A ID: B ID: C OrderConfirmed OrderPaid OrderChanged OrderCreated OrderConfirmed OrderPaid OrderChanged OrderCreated
62. 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)
63. 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)
64. class OrderServiceImpl(persistentEntityRegistry: PersistentEntityRegistry)(implicit ec: ExecutionContext) extends OrderService { override def payOrder(orderId: String): ServiceCall[ConfirmOrderRequest, NotUsed] = ServiceCall { req => persistentEntityRegistry.refFor[OrderEntity](orderId).ask(POrderCommand.PayOrder(req.paymentReference)).map(_ => NotUsed) } 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.isInstanceOf[POrderEvent.OrderCreated] || e.event == POrderEvent.OrderPaid ).mapAsync(1) { event => event.event match { case POrderEvent.OrderCreated(orderLines, shippingInfo) => val message = api.OrderEvent.OrderCreated(event.entityId, orderLines.map(x => api.Order.OrderLine(api.Order.SKU(x.sku.id), x.amount)), ShippingInfo(shippingInfo.address, shippingInfo.zipcode, shippingInfo.city, shippingInfo.country)) Future.successful((message, event.offset)) case x: POrderEvent.OrderPaid => persistentEntityRegistry.refFor[OrderEntity](event.entityId).ask(POrderCommand.GetOrder).map { x => val shippingInfo = x.shippingInfo.getOrElse(throw new Exception("Shipping info is expected to be set when the order is confirmed")) 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.city, shippingInfo.country) ) (message, event.offset) } } } } }
65. Order Shipping Message Broker OrderPaid PickOrder OrderPaid
66. Order Order Picked Whenever an Order is Paid Pick Order Order Order Paid Pay Order Order Shipping
67. Order Shipping Message Broker OrderPaid PickOrder OrderPaid Policy
68. 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) }
69. Purposes are deduced from behaviour, not from rhetoric or stated goals — Donella H. Meadows
70. Autonomy is reached by implementing policies for behaviour instead of commanding behaviour
71. In this, we can treat REST as an anti-pattern for domain to domain communication
72. As long as events are readable on a topic, the origin is of less importance
73. Decouples behaviour, communication from structure
74. Events-first delivers on a better way of modelling businesses in technology, while getting the rest for free
75. Q&A