Event-Driven-Architecture

Building a Robust Reservation System with Event-Driven Architecture In this post, I’ll guide you through creating a scalable reservation system using event-driven architecture. We’ll explore domain modeling, event handling, and message processing - essential concepts for modern distributed systems. The Reservation Process Flow Let’s start by visualizing the reservation workflow with a Mermaid diagram: flowchart TD A[Start Reservation Process] --> B[Receive Reservation Request] B --> C{Validate Request} C -->|Valid| D[Check Availability] C -->|Invalid| E[Return Error to Client] D --> F{Availability?} F -->|Available| G[Create Reservation] F -->|Not Available| H[Notify Client of Unavailability] G --> I[Send Confirmation via Wolverine] H --> I I --> J[Store Reservation in Postgres] J --> K[Return Success Response to Client] E --> L[End Process] K --> L This diagram shows the end-to-end process from receiving a request to returning a response, with key decision points and actions along the way. ...

Designing an event-based system with Wolverine is an exciting challenge that leverages asynchronous messaging to decouple components and build a resilient architecture. Here’s a comprehensive pathway to help you get started: 1. Understand the Role of Wolverine Wolverine is a lightweight, .NET-native messaging framework designed to help you craft robust, event-driven applications. It facilitates: Message Routing: Seamlessly route events and commands to corresponding handlers. Transport Flexibility: Integrate with in-memory queues or external messaging systems such as RabbitMQ or Azure Service Bus. Resilience and Durability: Apply advanced patterns like retry, scheduling, and outbox support if needed. By using Wolverine, you can focus on business logic while the framework handles much of the messaging infrastructure. ...

Here’s an example of a Business Event Flow Diagram tailored to a reservation system, illustrating how a typical business event (e.g., “Customer makes a reservation”) flows through the organization: flowchart TD %% Event Trigger Customer[Customer Initiates Reservation] --> SubmitRequest[Submit Reservation Request] SubmitRequest --> ValidateInputs[Validate Input Data] ValidateInputs -->|Valid| CheckAvailability[Check Resource Availability] ValidateInputs -->|Invalid| RejectRequest[Reject Request with Error] CheckAvailability -->|Available| ProcessReservation[Process Reservation] CheckAvailability -->|Not Available| NotifyUnavailability[Notify Customer of Unavailability] ProcessReservation --> CreateEvent[Create Business Event: ReservationCreated] CreateEvent --> NotifyCustomer[Send Confirmation Notification] CreateEvent --> UpdateDB[Update Reservation Database] NotifyCustomer --> End[End] UpdateDB --> End[End] NotifyUnavailability --> End[End] RejectRequest --> End[End] Key Elements: Event Trigger: The workflow begins when the customer initiates the reservation request. ...

Message Envelopes in Message-Based Software Development In message-based software development, message envelopes are a design pattern used to wrap the core message with additional metadata. This metadata helps the messaging system process, route, or interpret the message without needing to understand its actual content. Key Features of Message Envelopes Header and Body Separation: The header contains metadata like routing information, encryption details, or timestamps. The body holds the actual message payload. Flexibility: ...

Practical Applications of the Clock-Bound Wait Pattern The Clock-Bound Wait pattern is crucial in distributed systems to ensure data consistency, event ordering, and reliable operations across different nodes. Here are some practical applications: CloudEvents CloudEvents is a specification designed to provide a consistent and standardized way to describe event data across different systems. The main goal of CloudEvents is to ensure interoperability between cloud services, platforms, and applications by defining a common event format. ...

Below is an example of a Mermaid diagram that shows a high-level context diagram for our event-based reservation system using Wolverine. In this diagram, you can see external actors (like customers, an administrator, payment gateway, etc.) interacting with internal components such as a Reservation Frontend, Reservation Service, and the Wolverine Event Bus responsible for handling events. flowchart LR %%External Actors Customer[Customer] PaymentGateway[Payment Gateway] NotificationService[Notification Service] Administrator[Administrator] ResourceCatalog[Resource Catalog] %%Internal System Components subgraph System [Reservation System] Frontend[Reservation Frontend] Service[Reservation Service] EventBus[Wolverine Event Bus] end %%Interactions between External Actors and the System Customer -->|Creates/Manages Booking| Frontend Frontend --> Service Service -->|Publishes Events| EventBus EventBus -->|Notifies| PaymentGateway EventBus -->|Notifies| NotificationService Service -->|Checks Availability| ResourceCatalog Administrator -->|Manages System| Service Explanation External Actors: ...

Here is a Use Case Diagram for our reservation system, which visualizes the interactions between users (actors) and the system’s functionalities (use cases). graph TD %% External Actors Customer[Customer] --> CreateReservation Customer --> CancelReservation Customer --> ViewReservationDetails Customer --> ReceiveNotifications Administrator[Administrator] --> ManageResources Administrator --> GenerateReports Administrator --> ViewCustomerDetails %% System subgraph ReservationSystem [Reservation System] CreateReservation[Create Reservation] CancelReservation[Cancel Reservation] ViewReservationDetails[View Reservation Details] ReceiveNotifications[Receive Notifications] ManageResources[Manage Resources] GenerateReports[Generate Reports] ViewCustomerDetails[View Customer Details] end Explanation of the Diagram Actors: ...

Here’s an example of a Flowchart that represents a simple workflow for a reservation system, illustrating key steps in the booking process. graph TD Start[Start] --> EnterDetails[Customer Enters Reservation Details] EnterDetails --> CheckAvailability[Check Resource Availability] CheckAvailability -->|Available| ProceedPayment[Proceed with Payment] CheckAvailability -->|Not Available| DisplayError[Display Error Message] ProceedPayment --> ConfirmReservation[Confirm Reservation] ConfirmReservation --> SendNotification[Send Confirmation Notification] SendNotification --> End[End] Explanation of the Workflow: Start: The process begins when a customer initiates a reservation. Enter Details: The customer provides reservation details (e.g., date, time, resource). Check Resource Availability: The system verifies if the requested resource is available. If available, the workflow proceeds to payment. If not available, an error message is displayed to the customer. Proceed with Payment: The customer completes the payment process. Confirm Reservation: The system confirms the reservation after successful payment. Send Notification: A confirmation message (email/SMS) is sent to the customer. End: The workflow concludes.

Below is an example of an Architecture Diagram for our event-driven reservation system, illustrating a microservices architecture. It highlights the relationships between components, external systems, and underlying patterns used. flowchart TB %% External Clients Customer[Customer Frontend] Admin[Administrator Panel] %% Gateway Layer subgraph Gateway[API Gateway] GatewayService[Routing & Security] end %% Service Layer subgraph ServiceLayer[Service Layer] ReservationService[Reservation Service] ResourceService[Resource Catalog Service] NotificationService[Notification Service] PaymentService[Payment Service] end %% Event Handling Layer subgraph EventLayer[Event Handling Layer] EventBus[Wolverine Event Bus] end %% Data Layer subgraph DataLayer[Data Layer] ReservationDB[Reservations Database] ResourceDB[Resources Database] CustomerDB[Customers Database] end %% External Services ExternalNotification[Third-Party Notification System] ExternalPaymentGateway[Third-Party Payment Gateway] %% Interactions Customer --> GatewayService Admin --> GatewayService GatewayService --> ReservationService GatewayService --> ResourceService ReservationService --> ReservationDB ResourceService --> ResourceDB ReservationService --> CustomerDB ReservationService --> EventBus EventBus --> NotificationService EventBus --> PaymentService NotificationService --> ExternalNotification PaymentService --> ExternalPaymentGateway Breakdown of the Diagram External Clients: ...

Below is a Mermaid diagram that outlines a component diagram for your event-based reservation system using Wolverine. This diagram breaks down the core components and shows how they interact with each other and with external systems. graph TD %% External Systems PG[Payment Gateway] NS[Notification Service] RC[Resource Catalog] %% Reservation System Components subgraph Reservation_System [Reservation System] FE[Reservation Frontend] RS[Reservation Service] DO[Durable Outbox] EB[Wolverine Event Bus] EH[Event Handlers] end %% Internal Interactions FE -->|User Requests| RS RS -->|Persists Events/Commands| DO RS -->|Publishes Events| EB EB --> EH RS -->|Checks Availability| RC %% External Interactions via Event Bus EB -->|Notifies| PG EB -->|Notifies| NS Explanation Reservation System Components: ...

Here’s an example of a Level-1 Data Flow Diagram (DFD) for our reservation system. It highlights how data moves between external entities, processes, and storage components. flowchart TD %% External Entities Customer[Customer] ResourceCatalog[Resource Catalog] PaymentGateway[Payment Gateway] NotificationService[Notification Service] %% Processes Process1[Submit Reservation] Process2[Check Resource Availability] Process3[Process Payment] Process4[Notify Customer] %% Data Stores D1[Reservation Data Store] D2[Customer Data Store] %% Data Flows Customer -->|Reservation Details| Process1 Process1 -->|Reservation Data| D1 Process1 -->|Customer Details| D2 Process1 -->|Resource Details| Process2 ResourceCatalog -->|Resource Availability| Process2 Process2 -->|Reservation Confirmation| Process1 Process1 -->|Payment Info| Process3 PaymentGateway -->|Payment Status| Process3 Process3 -->|Notification Request| Process4 Process4 -->|Notification| NotificationService Explanation External Entities: ...

Below is an example of a Mermaid class diagram representing the core classes for our event-based reservation system to visualize the relationships between the entities, services, and events. classDiagram %% Domain Entities class Customer { +int Id +string FullName +string Email } class Resource { +int Id +string Name +string Description } class Reservation { +int Id +int CustomerId +int ResourceId +DateTime StartDate +DateTime EndDate +ReservationStatus Status } %% Service Layer class ReservationService { +CreateReservation(customerId: int, resourceId: int, startDate: DateTime, endDate: DateTime) Reservation +CancelReservation(reservationId: int) bool } %% Domain Events class ReservationCreatedEvent { +Guid ReservationId +DateTime CreatedAt +int CustomerId } class ReservationCancelledEvent { +Guid ReservationId +DateTime CancelledAt +int CustomerId } %% Event Handling Component class ReservationEventHandler { +Handle(event: ReservationCreatedEvent) +Handle(event: ReservationCancelledEvent) } %% Associations Customer "1" --o "0..*" Reservation : creates Resource "1" --o "0..*" Reservation : assigned to ReservationService ..> ReservationCreatedEvent : publishes ReservationService ..> ReservationCancelledEvent : publishes ReservationEventHandler ..> ReservationCreatedEvent : handles ReservationEventHandler ..> ReservationCancelledEvent : handles %% Note: ReservationStatus is an enumeration (e.g., Pending, Confirmed, Cancelled) Explanation Domain Entities: ...

Below is a Mermaid sequence diagram that showcases how components of our event-based reservation system interact during a typical workflow. This example outlines the process of a customer creating a reservation and includes key components such as the frontend, service layer, Wolverine event bus, and external systems. sequenceDiagram participant Customer participant Frontend participant Service as Reservation Service participant EventBus as Wolverine Event Bus participant ResourceCatalog participant Notification as Notification Service Customer ->> Frontend: Request to create a reservation Frontend ->> Service: Submit reservation details Service ->> ResourceCatalog: Check resource availability ResourceCatalog -->> Service: Availability status Service ->> Service: Validate and process reservation Service ->> EventBus: Publish ReservationCreated event EventBus ->> Notification: Notify customer of confirmation EventBus -->> Service: Acknowledge event publishing Service -->> Frontend: Return confirmation to customer Frontend -->> Customer: Display confirmation details Explanation of the Workflow Customer Interaction: ...

Below is a System Sequence Diagram for a reservation system, which highlights the interaction between external actors (e.g., customer, administrator) and the system during a reservation workflow: sequenceDiagram participant Customer participant System as Reservation System Customer ->> System: Enter reservation details System -->> Customer: Validate inputs Customer ->> System: Submit reservation request System ->> System: Check resource availability alt Resource available System ->> System: Create reservation System ->> Customer: Confirm reservation System ->> System: Trigger payment process System ->> Customer: Notify payment status else Resource not available System ->> Customer: Display unavailability message end Explanation of the Diagram: Actors and System: ...

Here’s an example of a State Diagram for a reservation system object. This illustrates the states that a reservation can move through and the transitions triggered by events or actions. stateDiagram-v2 state "Pending" as Pending state "Confirmed" as Confirmed state "Cancelled" as Cancelled state "Completed" as Completed %% State Transitions Pending --> Confirmed: Payment Received Pending --> Cancelled: Customer Cancels Confirmed --> Cancelled: Customer Cancels Confirmed --> Completed: Reservation Period Ends Cancelled --> Pending: Reopen Request Explanation of States and Transitions: States: ...

Below is an example of a deployment diagram for our event-based reservation system. This shows how components of the system are deployed across servers, environments, and external services in a physical setup. You can use the following Mermaid code to visualize it in a Mermaid-enabled renderer: graph TD %% Deployment Nodes subgraph ClientMachine [Client Machine] FrontendApp[Reservation Frontend App] end subgraph AppServer [Application Server] ReservationService[Reservation Service] WolverineEventBus[Wolverine Event Bus] DurableOutbox[Durable Outbox] end subgraph Messaging [Messaging Infrastructure] MessageBroker[Message Broker] end subgraph DatabaseServer [Database Server] ReservationsDB[Reservations Database] CustomersDB[Customers Database] end subgraph ExternalServices [External Systems] PaymentGateway[Payment Gateway] NotificationService[Notification Service] ResourceCatalog[Resource Catalog Service] end %% Interactions FrontendApp --> ReservationService ReservationService --> WolverineEventBus WolverineEventBus --> DurableOutbox WolverineEventBus --> MessageBroker MessageBroker --> PaymentGateway MessageBroker --> NotificationService ReservationService --> ReservationsDB ReservationService --> CustomersDB ReservationService --> ResourceCatalog Explanation Nodes: ...

Here is a conceptual Entity-Relationship Diagram (ERD) for our conceptual reservation system. This diagram includes entities such as Customer, Reservation, and Resource, along with their attributes and relationships. erDiagram %% Customer Entity Customer { int Id string FullName string Email string Phone } %% Resource Entity Resource { int Id string Name string Description int Capacity } %% Reservation Entity Reservation { int Id int CustomerId int ResourceId DateTime StartDate DateTime EndDate string Status } %% Relationships Customer ||--o{ Reservation : "creates" Resource ||--o{ Reservation : "associated with" Explanation Entities: ...

Below is an example of an Infrastructure Diagram that illustrates how our event-based reservation system might be deployed using cloud resources. This includes virtual machines, networks, containers, and external services. graph TD %% Cloud Platform subgraph CloudInfrastructure[Cloud Infrastructure -e.g., AWS, Azure, GCP-] LB[Load Balancer] VPC[VPC -Virtual Private Cloud-] subgraph AppLayer[Application Layer] EC2Instance1[Virtual Machine: Reservation Service Instance 1] EC2Instance2[Virtual Machine: Reservation Service Instance 2] Container1[Docker Container: Wolverine Event Bus] Container2[Docker Container: Durable Outbox] end subgraph DataLayer[Data Layer] DBCluster[Managed Database Cluster] BackupStorage[Cloud Backup Storage] end subgraph ExternalServices[External Integrations] PaymentGateway[Payment Gateway] NotificationService[Notification Service] ResourceCatalog[Resource Catalog API] end end %% Interactions LB --> EC2Instance1 LB --> EC2Instance2 EC2Instance1 --> Container1 EC2Instance2 --> Container2 EC2Instance1 --> DBCluster DBCluster --> BackupStorage Container1 --> PaymentGateway Container2 --> NotificationService EC2Instance1 --> ResourceCatalog Explanation of Components: Cloud Infrastructure: ...

Below is an example of a Network Diagram that depicts a possible topology for our reservation system, illustrating firewalls, routers, subnets, and connections. It is designed to enhance network security and efficiency. graph TB %% Internet Internet[Internet] --> Firewall1[Firewall] %% Perimeter Network -DMZ subgraph DMZ[Perimeter Network -DMZ-] Router[Router] APIGateway[API Gateway] end Firewall1 --> Router Router --> APIGateway %% Internal Network subgraph InternalNetwork[Internal Network] LoadBalancer[Load Balancer] ApplicationServer1[App Server 1] ApplicationServer2[App Server 2] DatabaseServer[Database Server] EventBus[Wolverine Event Bus] end APIGateway --> LoadBalancer LoadBalancer --> ApplicationServer1 LoadBalancer --> ApplicationServer2 ApplicationServer1 --> DatabaseServer ApplicationServer2 --> DatabaseServer ApplicationServer1 --> EventBus ApplicationServer2 --> EventBus %% External Services subgraph ExternalServices[External Services] NotificationService[Notification Service] PaymentGateway[Payment Gateway] end EventBus --> NotificationService EventBus --> PaymentGateway Components Breakdown: Internet: ...