DDDVienna - Applying event sourcing and CQRS in a large ERP system

In the last 7 years we have applied event sourcing and CQRS in the development of our new ERP system. During this process we have run into some interesting challenges and we have come up with solutions. In this session I would like to present these patterns and get your feedback on them.

Transcript

1. Applying event sourcing and CQRS in a large ERP system
   Our work at AFAS Software
   

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2. 400+ employees (4 locations)
   10.500 customers (companies)
   AFAS Software
   

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3. HRM, CRM, finance, order
   management, project
   management, workflow, ...
   AFAS Profit
   

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4. 1996 – AFAS starts
   2011 (jan) – First steps in CQRS and event sourcing
   2011 (dec) – Started at AFAS
   2020 – Live
   Via JTeam/Trifork/Axon.
   2016 – Started on evolution
   

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5. 20 years of ERP
   10.000 customers
   90% cloud
   Web
   Scalable
   CQRS
   Event sourcing
   

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6. 20 years of ERP
   10.000 customers
   90% cloud
   Person
   Entity
   Customer
   Role
   Order
   Agreement
   party
   Spending limit
   Address
   Organisation
   Entity
   Delivery
   BusinessAc tivity
   party
   Invoice
   BusinessAc tivity
   party
   Address
   Address
   Spending limit
   Spending limit
   Own Organisation
   Workarea
   workarea
   Spending limit
   Put all our knowledge and
   experience in a model
   

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7. Customized
   Web
   Scalable
   CQRS
   Event sourcing
   Person
   Entity
   Customer
   Role
   Order
   Agreement
   party
   Spending limit
   Address
   Organisation
   Entity
   Delivery
   BusinessAc tivity
   party
   Invoice
   BusinessAc tivity
   party
   Address
   Address
   Spending limit
   Spending limit
   Own Organisation
   Workarea
   workarea
   Spending limit
   

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8. (2.830 tables with 126.705 columns)
   ERP software is inherently relational
   

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9. Our basic CQRS/Event Sourcing solution
   

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10. Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Event Queue
    Query
    request
    Query
    handler
    

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11. Event store
    Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Event Queue
    Query
    request
    Query
    handler
    Aggregate
    root
    Command Projector
    Event Queue
    Query store
    

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12. Event store
    Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Event Queue
    Query
    request
    Query
    handler
    Aggregate
    root
    Command Projector
    Event Queue
    Query store
    Data of different projectors can not be joined.
    Tables are fully inlined, no joins.
    

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13. Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Event Queue
    Query
    request
    Query
    handler
    • Aimed at CRUD
    • MongoDB, *SQL, DocumentDB
    • MS Orleans, MS Service Fabric
    • SPA-frontend
    

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14. How about evolution? Part 1
    

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15. Evolution as a feature of the model?
    Person
    Entity
    Customer
    Role
    Order
    Agreement
    party
    Spending limit
    Address
    Organisation
    Entity
    Delivery
    BusinessAc tivity
    party
    Invoice
    BusinessAc tivity
    party
    Address
    Address
    Spending limit
    Spending limit
    Own Organisation
    Workarea
    workarea
    Spending limit
    

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16. Data
    upgrade
    Deployed with
    Executed by
    Executed by
    Data
    upgrade
    Application upgrade
    Lazy transformation
    Upcasting
    In place
    transfor-
    mation
    Multiple versions
    Copy and
    transfor-
    mation
    Basic &
    Complex
    Event
    Basic &
    Complex
    Stream
    Basic
    Store
    Complex
    Store
    Big Flip
    Rolling
    Upgrade
    Blue-Green
    Expand-
    Contract
    Blue-
    Green
    Deployed with
    Combined with
    Weak schema
    Expensive!
    

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17. Event Publishing part 2
    

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18. Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Event Queue
    Query
    request
    Query
    handler
    

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19. Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Event Queue
    Query
    request
    Query
    handler
    Can give error (needs retry).
    Command-side in control
    over publishing.
    

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20. Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Query
    request
    Query
    handler
    

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21. Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Query
    request
    Query
    handler
    Projector in control.
    More load on the event store.
    

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22. When CRUD is not enough
    business processes
    

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23. Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Query
    request
    Query
    handler
    

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24. Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Query
    request
    Query
    handler
    Process
    manager
    

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25. Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Query
    request
    Query
    handler
    Process
    manager
    But what if these
    commands fail?
    

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26. Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Query
    request
    Query
    handler
    Process
    manager
    Event store
    

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27. Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Query
    request
    Query
    handler
    Process
    manager
    Event store
    Commands that cannot
    fail become events. We
    still have some internal
    commands.
    

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28. Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Query
    request
    Query
    handler
    Process
    manager
    Event store
    Different instances to
    scale the work.
    Event sourced for state.
    

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29. Aggregate
    root /
    Process
    manager
    Command
    Event store
    Event
    Projector
    Query store
    Query
    request
    Query
    handler
    Is this what we want?
    

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30. Aggregate
    root /
    Process
    manager
    Command
    Event store
    Event
    Projector
    Query store
    Query
    request
    Query
    handler
    Is this what we want?
    Technically there is no
    difference between
    aggregates and
    processmanagers
    

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31. The problem of relational data
    

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32. Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Query
    request
    Query
    handler
    Process
    manager
    Event store
    

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33. Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Query
    request
    Query
    handler
    Process
    manager
    Event store
    Process
    manager
    Process
    manager
    Process
    manager
    Aggregate
    root
    Aggregate
    root
    Aggregate
    root
    Aggregate
    root
    

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34. Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Query
    request
    Query
    handler
    Process
    manager
    Event store
    Process
    manager
    Process
    manager
    Process
    manager
    Aggregate
    root
    Aggregate
    root
    Aggregate
    root
    Aggregate
    root
    These ProcessManager
    all need the same data
    (lots of data)
    

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35. Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Query
    request
    Query
    handler
    Process
    manager
    Event store
    Stream
    Projector Query store
    Event store
    

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36. Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Query
    request
    Query
    handler
    Process
    manager
    Event store
    Stream
    Projector Query store
    Event store
    StreamProjectors are
    single-instanced, non-
    event-sourced
    processmanagers
    

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37. Eventual consistency
    communication between client and server
    

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38. Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Query
    request
    Query
    handler
    Client
    

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39. Counter
    Process
    Manager
    Count
    Command
    Counted
    Event
    Event store
    Counter
    Projector
    Query store
    Get
    Counter
    Count
    Query
    handler
    Getting the next
    consecutive number in a
    series.
    

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40. Counter
    Process
    Manager
    Count
    Command
    Counted
    Event
    Event store
    Counter
    Projector
    Query store
    Get
    Counter
    Count
    Query
    handler
    When is the value ready?
    Correlationid?
    

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41. Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Query
    request
    Query
    handler
    Client
    Using websockets to
    notify the Client
    

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42. Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Query
    request
    Query
    handler
    Client
    Returning values from
    the produced event
    directly
    

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43. Counter
    Process
    Manager
    Count
    Command
    Counted
    Event
    Event store
    Counter
    Projector
    Query store
    Get
    Counter
    Count
    Query
    handler
    

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44. How large is our system anyway?
    

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45. Aggregate
    root
    Command
    Event store
    Event
    Projector
    Query store
    Query
    request
    Query
    handler
    Stream
    Projector Query store
    Event store
    557
    464
    1927
    4849
    1075
    2718
    801
    1479
    

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46. Store (19)
    S M L
    Traffic (19)
    S M L
    Schema (14)
    S M L
    

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47. Dealing with bounded contexts
    

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49. Aggregate
    root
    Command
    Event store
    Event
    Aggregate
    root
    Event store
    Event
    

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50. Aggregate
    root
    Command
    Event store
    Event
    Aggregate
    root
    Event store
    Event
    Team B
    Team A
    

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51. Aggregate
    root
    Command
    Event store
    Event
    Aggregate
    root
    Event store
    Event
    These events now serve multiple goals.
    Team B
    Team A
    

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52. Aggregate
    root
    Command
    Event store
    Event
    Aggregate
    root
    Event store
    Event
    Team B
    Team A
    Sync
    Event store
    Event
    

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53. Aggregate
    root
    Command
    Event store
    Event
    Aggregate
    root
    Event store
    Event
    Team B
    Team A
    Sync
    Event store
    Event
    Introduce synchronization events.
    

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54. How about evolution? Part 2
    

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55. Versioned
    Events
    Weak
    Schema
    Upcasters In-Place
    Copy-
    Transform
    

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56. We will go live in January…
    No guarantees are given ☺
    

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57. Copyright Nasa Goddard
    Michiel Overeem
    @michielovereem
    • No event bus
    • Commands do have results
    • Projectors can publish events
    • Aggregates can listen to events
    • You can do what you want ☺
    i.e. you do not have to
    listen to a consultant that
    does not know your
    context.
    

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