Building modular monoliths that could scale to microservices (only if they need to) .jax munich-21
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David Gómez discusses the process of building scalable monolith applications transitioning to microservices when necessary, emphasizing avoiding hype-driven development (HDD). He outlines critical steps such as understanding problems, employing Command Query Responsibility Segregation (CQRS), and event sourcing to achieve clear separation of commands and queries. The document includes examples of a conference management tool and various aggregates and commands that illustrate the practical application of these architectural concepts.
Building modular monoliths that could scale to microservices (only if they need to) .jax munich-21
- 1. David Gómez G. Developer Advocate . Building monolith applications that can scale to micro services (only if they need to) @AXONIQ @DGOMEZG
- 2. Don’t let the microservices hype ruin your project @AXONIQ @DGOMEZG David Gómez G. Developer Advocate .
- 3. An Exciting New Project Starts @DGOMEZG
- 4. Or you may need to add a new module/feature to an existing project @DGOMEZG
- 5. But this time, you are going to get it right! @DGOMEZG
- 6. We need to scale! We need to go to the cloud(s)! @DGOMEZG
- 7. How others solved similar problems? @DGOMEZG
- 11. You will probably be missing all of these @DGOMEZG
- 13. Problems seem easier to solve when you have enough context @DGOMEZG
- 14. we don’t usually know enough @DGOMEZG @DGOMEZG
- 15. we don’t usually know enough @DGOMEZG
- 16. @DGOMEZG What you need (Your steps) • Separate your different tasks by type • Focus on understanding the problem(s) you need to solve, • Model each problem independently • Be prepared to grow & scale (both in features and in performance) • Don’t couple to other components
- 17. @DGOMEZG Our example: A Conference Management Tool.
- 18. @DGOMEZG Our example: A Conference Management Tool. Dates, Sponsors, Call For Papers, Proposals, Agenda T alks, Tickets, Attendees… Call For Papers, Agenda, Questions, Forums, Tickets, Agenda, speakers, …
- 20. @DGOMEZG Command Query Responsibility Separation CQRS
- 21. @DGOMEZG COMMANDS QUERIES CQRS Separate Queries from Commands @DGOMEZG
- 22. @DGOMEZG CQRS Separate Queries from Commands COMMANDS What actions do require changes in the state of the application? What other changes will be necessary to notify/propagate? @DGOMEZG
- 23. @DGOMEZG CQRS Separate Queries from Commands COMMANDS Define Edition (Dates) Accept/Reject Talk Proposal Open Ticket sales Open Call For Papers Add/Remove Track Define Q&A Channel Submit Proposal Withdraw Proposal Confirm Proposal Join Q&A Channel Buy Ticket Add Talk To My Agenda Ask Questions in Q&A. Rate Talk @DGOMEZG
- 24. @DGOMEZG CQRS Separate Queries from Commands QUERIES What information do the users require? @DGOMEZG
- 25. @DGOMEZG CQRS Separate Queries from Commands QUERIES List Proposals Get Talk Popularity Get Talks Rating Get Questions Get Talk Feedback My Talk Info Conference Agenda My Agenda Q&A Messages @DGOMEZG
- 29. Which map would you prefer? It depends! @DGOMEZG
- 30. @DGOMEZG COMMANDS QUERIES Focus on modelling within the boundaries of each element Command model Projections Keep only relevant information for the action in each model @DGOMEZG
- 31. @DGOMEZG JoinRoom JoinRoom Send Message Command model CreateChatRoom NAME, DESCRIPTION USER, ROOMID, MSG JoinRoom USERID, ROOMID @DGOMEZG
- 32. @DGOMEZG Projections Projections maintain the structure of information close to how it is needed by the client/user ListRooms ROOM, DESCRIPTION, NUM_OF_MEMBERS GetRoomMessages DATE, USER, MSG DATE, USER, MSG DATE, USER, MSG @DGOMEZG
- 33. @DGOMEZG Aggregate A set of objects, relationship and invariants that are considered as one unit with regard to data changes. Define the boundaries in which some invariants are kept. They are a model of part of the domain. @DGOMEZG
- 35. @DGOMEZG Queries UI / API Commands Command Model Projections ? @DGOMEZG
- 36. @DGOMEZG Notify that something has happened Events
- 37. Remember our micro services architecture? @DGOMEZG
- 38. Remember our micro services architecture? @DGOMEZG
- 39. Remember our micro services architecture? @DGOMEZG
- 40. Remember our micro services architecture? @DGOMEZG
- 41. Remember our micro services architecture? Event @DGOMEZG
- 42. @DGOMEZG Queries UI / API Commands Command Model Projections ? @DGOMEZG
- 43. @DGOMEZG Queries UI / API Commands Command Model Projections Events @DGOMEZG
- 46. Event-Sourcing
- 48. @DGOMEZG With state store id: 123. Author: John Doe Title: What’s new in Java 17 status: Withdrawn What we store
- 49. @DGOMEZG Why Event-Sourcing? ProposalUpdated (id: 123, title, Smith) SpeakerChanged (id:123, jDoe) ProposalSubmitted ProposalAccepted ProposalWithdrawn ProposalDraftSent (id: 123) id: 123. Author: John Doe Title: What’s new in Java 17 status: Withdrawn What happened What we store
- 50. @DGOMEZG Why Event-Sourcing? Business Reasons Technical reasons • Reliability of decisions • Auditing / compliance / transparency • Data mining, analytics: value for data • Historic data useful for new features • Guaranteed completeness of event stream • Single point of truth • Concurrency / conflict resolution • Facilitates debugging / forensic analysis • Replay into new read models (scalability with CQRS)
- 53. Location Transparency A component should neither be aware of nor make any assumptions about the location of other components Furthermore, it should not even know which components it interacts with @DGOMEZG
- 54. @DGOMEZG
- 55. @DGOMEZG 1. Keep the independent models
- 56. @DGOMEZG 1. Keep the independent models
- 57. @DGOMEZG 1. Keep the independent models
- 58. @DGOMEZG 1. Keep the independent models CQRS + DDD
- 59. @DGOMEZG Event Sourcing (sync modules) + Message Bus Event store
- 61. @DGOMEZG Command Model data class CreateRoomCommand( @TargetAggregateIdentifier val roomId: String, val name: String) data class JoinRoomCommand( @TargetAggregateIdentifier val roomId: String, val participant: String) data class PostMessageCommand( @TargetAggregateIdentifier val roomId: String, val participant: String, val message: String) data class LeaveRoomCommand( @TargetAggregateIdentifier val roomId: String, val participant: String)
- 62. @DGOMEZG Event Model data class RoomCreatedEvent( val roomId: String, val name: String) data class ParticipantJoinedRoomEvent( val roomId: String, val participant: String) data class MessagePostedEvent( val roomId: String, val participant: String, val message: String) data class ParticipantLeftRoomEvent( val roomId: String, val participant: String)
- 63. @DGOMEZG Aggregate @Aggregate public class ChatRoom { @AggregateIdentifier private String roomId; private Set<String> participants; public ChatRoom() { } }
- 64. @DGOMEZG Aggregate: Handling a Command @Aggregate public class ChatRoom { @AggregateIdentifier private String roomId; private Set<String> participants; @CommandHandler public ChatRoom() { } }
- 65. @DGOMEZG Aggregate: Handling a Command @Aggregate public class ChatRoom { @AggregateIdentifier private String roomId; private Set<String> participants; @CommandHandler public ChatRoom(CreateRoomCommand command) { } }
- 66. @DGOMEZG Aggregate: Handling a Command @Aggregate public class ChatRoom { @AggregateIdentifier private String roomId; private Set<String> participants; @CommandHandler public ChatRoom(CreateRoomCommand command) { apply(new RoomCreatedEvent(command.getRoomId(), command.getName())); } }
- 67. @DGOMEZG Aggregate: Handling a Command @Aggregate public class ChatRoom { @AggregateIdentifier private String roomId; private Set<String> participants; @CommandHandler public ChatRoom(CreateRoomCommand command) { apply(new RoomCreatedEvent(command.getRoomId(), command.getName())); } @CommandHandler public void handle(JoinRoomCommand command) { } }
- 68. @DGOMEZG Aggregate: Handling a Command @Aggregate public class ChatRoom { @AggregateIdentifier private String roomId; private Set<String> participants; @CommandHandler public ChatRoom(CreateRoomCommand command) { apply(new RoomCreatedEvent(command.getRoomId(), command.getName())); } @CommandHandler public void handle(JoinRoomCommand command) { apply(new ParticipantJoinedRoomEvent(command.getRoomId(), command.getParticipant())); } }
- 69. @DGOMEZG Aggregate: Handling a Command @Aggregate public class ChatRoom { @AggregateIdentifier private String roomId; private Set<String> participants; @CommandHandler public void handle(JoinRoomCommand command) { apply(new ParticipantJoinedRoomEvent(command.getRoomId(), command.getParticipant())); } }
- 70. @DGOMEZG Aggregate: Handling a Command @Aggregate public class ChatRoom { @AggregateIdentifier private String roomId; private Set<String> participants; @CommandHandler public void handle(JoinRoomCommand command) { apply(new ParticipantJoinedRoomEvent(command.getRoomId(), command.getParticipant())); } @EventSourcingHandler public void on() { } }
- 71. @DGOMEZG Aggregate: Handling a Command @Aggregate public class ChatRoom { @AggregateIdentifier private String roomId; private Set<String> participants; @CommandHandler public void handle(JoinRoomCommand command) { apply(new ParticipantJoinedRoomEvent(command.getRoomId(), command.getParticipant())); } @EventSourcingHandler public void on(ParticipantJoinedRoomEvent event) { } }
- 72. @DGOMEZG Aggregate: Handling a Command @Aggregate public class ChatRoom { @AggregateIdentifier private String roomId; private Set<String> participants; @CommandHandler public void handle(JoinRoomCommand command) { apply(new ParticipantJoinedRoomEvent(command.getRoomId(), command.getParticipant())); } @EventSourcingHandler public void on(ParticipantJoinedRoomEvent event) { this.participants.add(event.getParticipant()); } }
- 73. @DGOMEZG Aggregate: Command Validation @Aggregate public class ChatRoom { @AggregateIdentifier private String roomId; private Set<String> participants; @CommandHandler public void handle(JoinRoomCommand command) { if (…) { apply(new ParticipantJoinedRoomEvent(command.getRoomId(), command.getParticipant())); } } @EventSourcingHandler public void on(ParticipantJoinedRoomEvent event) { this.participants.add(event.getParticipant()); } }
- 74. @DGOMEZG Location Transparency. Sync other components @Component public class RoomSummaryProjection { private final RoomSummaryRepository roomSummaryRepository; @EventHandler public void on(RoomCreatedEvent event) { roomSummaryRepository.save(new RoomSummary(event.getRoomId(), event.getName())); } @EventHandler public void on(ParticipantJoinedRoomEvent event) { roomSummaryRepository.findById(event.getRoomId()) .ifPresent(RoomSummary::addParticipant); } }
- 75. @DGOMEZG Handling Queries @Component public class RoomSummaryProjection { private final RoomSummaryRepository roomSummaryRepository; @QueryHandler public List<String> handle(RoomParticipantsQuery query) { return roomSumaryRepository.findRoomParticipants(query.getRoomId()) .stream() .map(RoomParticipant::getParticipant).sorted() .collect(toList())event.getName())); } }
- 80. @DGOMEZG Useful Resources https://lp.axoniq.io/w-jax-munich-2021 The slides Code-sample & tutorial repo Free DDD, CQRS & ES courses eventmodeling.org Domain-Driven Design lp.axoniq.io/w-jax-munich-2021 Axon OS tools