Gr8Conf: Implementing loosely coupled microservices with Grails

Grails 3 is s a great starting point for creating microservices and many projects are following this path. However many microservice landscapes are still based on synchronous calls to REST Resources which obviously increases coupling between those applications. This talk focusses on building loosely coupled microservices that are based on Domain Events, which are becoming more and more popular in the Domain Driven Design community. We will take a look at how Grails 3 helps us in building such systems by introducing the Grails 3 event system and by taking a look how we can leverage Domain Events for a decoupled communication between Grails applications.

Transcript

1. Loosely Coupled
   Microservices with Grails
   Michael Plöd
   @bitboss
   

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2. Interactions between Microserivces
   Grails App
   A
   Grails App
   B
   Typically RESTful HTTP
   

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3. Interactions between Microserivces
   Grails App
   A
   Grails App
   B
   Grails App
   C
   Grails Ap
   D
   Grails App
   E
   Grails App
   F
   

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4. Interactions between Microserivces
   Grails App
   A
   Grails App
   B
   Grails App
   C
   Grails Ap
   D
   Grails App
   E
   Grails App
   F
   !
   "
   #
   $
   %
   

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5. Welcome to the
   Dark Side
   

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6. Challenges
   !
   "
   #
   $
   %
   Service Discovery
   Timeouts
   Errors
   Latency
   Load Balancing
   &Stability
   

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7. Usual Architecture Patterns
   > Event-Driven Architecture
   > REST
   > SOA
   > Microservices / Self-Contained Systems
   > CQRS
   > Reactive / Actor Model
   

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8. Domain Events
   > Applications can issue Domain Events
   > Domain Events are important occurrences in an Domain
   > UserVerified
   > ShoppingCartCheckedOut
   > ShipmentDelivered
   > Domain Events are usually based on eventual consistency
   > Major driver for high degree of decoupling between
   Microservices
   

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9. Domain Events
   Customer

   Notification

   Application
   Shipping

   Application
   Shipment

   Delivered

   Event
   Messaging

   System
   Shipment

   Delivered

   Event
   

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10. An event is something 

    that happened in the past
    t
    now
    Event
    Event
    Event
    Event
    Event
    

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11. ShipmentDeliveredEvent

    CustomerVerifiedEvent
    CartCheckedOutEvent
    CreateCustomerEvent

    WillSaveItemEvent

    DoStuffEvent
    

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12. An Event is always immutable
    !
    

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13. Loan Details
    Entered
    Financial
    Situation
    Entered
    Personal
    Infromation
    Entered
    Application
    Submitted
    Credit

    Application
    Scoring
    …
    …
    

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14. Let’s reuse the ESB
    from the failed SOA
    project
    

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15. NO
    

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16. NO
    

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17. NO
    

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18. Talking about Grails
    

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19. Loan Details
    Entered
    Financial
    Situation
    Entered
    Personal
    Infromation
    Entered
    Application
    Submitted
    Use the 

    Grails 3 

    Event System
    for handling of
    internal Events
    Use 

    RabbitMQ 

    or 

    Kafka 

    for handling of
    external Events
    

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20. Options for Events
    Event with complete
    payload
    Event with a REST URL
    Empty Event as a Feed
    update notification
    > The Event contains all relevant data
    > Enables complete async processing
    > Payload is big and can fill up your message broker
    > The Event only contains a URL to a REST-Resource and some minimal
    data, that is usually always needed
    > Small payload that is fast to transport
    > Standard cases work completely asynchronous, more complex cases
    might require a synchronous roundtrip (without service lookup though)
    > The Event has no payload at all, it is just a notification
    > The payload, be it data or a REST URL, is usually contained in an
    Atom Feed
    > Event is a polling trigger for the feed
    

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21. https://github.com/mploed/event-driven-spring-boot
    Let’s replace the Scoring one
    with a Grails 3 Microservice!
    https://github.com/mploed/event-driven-grails
    

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22. THANK YOU
    I’ll post links to slides and code on Twitter

    Michael Plöd - innoQ
    @bitboss
    

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