.NET Event-Driven Architecture with EventStore
Learn how to build robust, scalable, and maintainable event-driven systems in .NET using EventStore.
Table of Contents
Introduction to Event-Driven Architecture
Event-Driven Architecture (EDA) is a design pattern that promotes the production, detection, and consumption of events to drive system behavior. It enables decoupled communication and improves scalability, maintainability, and responsiveness in distributed systems.
Why Use EventStore?
EventStore is a powerful, open-source database designed specifically for event sourcing. It offers features such as:
- Event persistence with strong consistency guarantees.
- Support for complex event-driven workflows.
- Scalable event storage and retrieval.
- Built-in projections for querying event streams.
- Integration with .NET through libraries like
EventStore.Client
.
Prerequisites
Before implementing EventStore in .NET, you need the following:
- Basic understanding of .NET Core and C#.
- Knowledge of event-driven design principles.
- A local or hosted instance of EventStore.
Setting Up EventStore
Step 1: Install EventStore
You can run EventStore locally using Docker:
docker run --name eventstore-node -d \ -p 2113:2113 -p 1113:1113 \ eventstore/eventstore:latest
Step 2: Access the Admin UI
Open http://localhost:2113 in your browser and log in with the default credentials.
Core Concepts in EventStore
- Streams: Logical containers for events, identified by unique names.
- Events: Immutable facts representing state changes.
- Projections: Real-time processing of event streams to generate derived data.
- Subscriptions: Mechanisms for clients to react to events in real time.
Implementing EventStore in .NET
Step 1: Install the Client Library
dotnet add package EventStore.Client
Step 2: Write Events to a Stream
using EventStore.Client; using System.Text.Json; // Configure the EventStore client var settings = EventStoreClientSettings.Create("esdb://localhost:2113?tls=false"); var client = new EventStoreClient(settings); var eventData = new EventData( Uuid.NewUuid(), "order-created", JsonSerializer.SerializeToUtf8Bytes(new { OrderId = "1234", Amount = 100 }) ); await client.AppendToStreamAsync("orders", StreamState.Any, new[] { eventData });
Step 3: Read Events from a Stream
var stream = client.ReadStreamAsync(Direction.Forwards, "orders", StreamPosition.Start); await foreach (var resolvedEvent in stream) { Console.WriteLine($"Event: {resolvedEvent.Event.EventType}, Data: {Encoding.UTF8.GetString(resolvedEvent.Event.Data.Span)}"); }
CQRS and Event Sourcing with EventStore
EventStore is an ideal choice for implementing CQRS (Command Query Responsibility Segregation) and Event Sourcing patterns. With EventStore:
- Commands: Trigger state changes by appending events to streams.
- Queries: Use projections to query materialized views.
- Rebuild State: Replay events to recreate the current state of an entity.
Best Practices
- Partition streams by aggregate ID to improve performance.
- Use metadata to store additional context with events.
- Leverage projections to create queryable data models.
- Monitor EventStore with built-in metrics and logs.
Conclusion
EventStore simplifies the implementation of event-driven systems in .NET. By following this guide, you can build scalable, maintainable, and efficient architectures that leverage the full power of event sourcing and CQRS.