EventServices

Introduction

Modern applications are increasingly event-driven rather than tightly coupled request-response systems. In cloud environments, event-driven architecture enables applications to react to changes instantly , scale efficiently, and remain loosely coupled. Microsoft Azure provides several services that make it easy to build event-driven systems. Combined with .NET 10 , developers can create scalable and resilient microservices that react to events such as file uploads, database updates, messages, or business actions.

This article explains event-driven services in Azure , when to use them, and how to implement them using .NET 10 with a real-world example and code samples .

What is Event-Driven Architecture?

Event-Driven Architecture (EDA) is a design pattern where services communicate through events instead of direct calls.

An event represents something that happened in the system.

Examples:

Instead of calling another service directly, the system publishes an event , and other services subscribe to it .

Key Components

  1. Event Producer : It generates the event for an example order service.

  2. Event Broker

    • Transports and distributes events.

    • Example: Azure Event Grid, Azure Service Bus.

  3. Event Consumer

    • Processes the event.

    • Example: Notification service.

Azure Services for Event-Driven Systems

Azure provides multiple services for building event-driven architectures.

1. Azure Event Grid

Event Grid is designed for event routing between services.

It supports:

Typical use cases:

Example events:

2. Azure Service Bus

It is used for reliable enterprise messaging .

Azure Service Bus has following features:

Best used for:

3. Azure Event Hubs

Event Hubs is designed for high-throughput event streaming .

It can process millions of events per second .

Common use cases:

4. Azure Functions

Azure Functions enable serverless event processing . Azure Functions automatically trigger when events occur.

Example triggers:

Real-World Example: E-Commerce Order Processing

Let's build a simple event-driven order system .

Scenario

When a customer places an order:

  1. Order Service publishes OrderCreated event

  2. Inventory Service reduces stock

  3. Notification Service sends email

  4. Billing Service processes payment

Instead of direct API calls, services communicate via Azure Service Bus Topic .

Architecture

  
    Order API (.NET 10)
      |
Publish Event
      |
Azure Service Bus Topic
      |
-------------------------------
|            |                |
Inventory    Notification     Billing
Service      Service          Service

Benefits of event-driven services/architecture

Project Example

Step 1: Create Solution Structure

Now, let's create a project for better understanding

ProjectPurpose
Order.ApiPublishes events
Order.EventsShared models
Order.FunctionsConsumes events

Step 2: Define Event Model

Let's create a new class OrderCreatedEvent.csin Order.Eventsproject.

public class OrderCreatedEvent
{
    public string OrderId { get; set; }
    public string Email { get; set; }
    public decimal Amount { get; set; }
}

This represents the event payload. Whenever an order is created, this object is sent to Azure Event Grid.

Step 3: Create Event Publisher (API)

Now, let's create minimal API project Order.API

Create event publisher API in the API project as following. Let's add below code in the Program.cs class.

app.MapPost("/orders", async (OrderCreatedEvent order) =>
{
    var client = new EventGridPublisherClient(
        new Uri(topicEndpoint),
        new AzureKeyCredential(topicKey));    
        var eventGridEvent = new EventGridEvent(
        subject: "Order.Created",
        eventType: "OrderCreatedEvent",
        dataVersion: "1.0",
        data: order);    
        await client.SendEventAsync(eventGridEvent);    
        return Results.Ok("Order event published");
});

In this scenario,

Step 4: Create Azure Event Grid Topic

Now we need to create Azure Event Grid Topic. So, go to Azure Portal:

  1. Create resource → Event Grid Topic

  2. Copy:

    • Topic Endpoint

    • Access Key

Update in your API:

string topicEndpoint = "YOUR_ENDPOINT";
 string topicKey = "YOUR_KEY";

Step 5: Create Azure Function (Consumer)

Let's create a Azure function project Order.Functions and create OrderCreatedHandler.cs.

[Function("OrderCreatedHandler")]
public void Run([EventGridTrigger] EventGridEvent eventGridEvent)
{
    var order = eventGridEvent.Data.ToObjectFromJson<OrderCreatedEvent>(); 
   _logger.LogInformation($"Order received: {order.OrderId}");
}

Step 6: Subscribe Function to Event Grid

In Azure Portal:

  1. Open Event Grid Topic

  2. Click + Event Subscription

  3. Select:

    • Endpoint Type → Azure Function

    • Choose your deployed function

Now your function will receive events automatically.

Here:

Step 7: Run the System

Start API

dotnet run --project Order.Api

Then send request.

{
  "orderId": "101",
  "email": "[email protected]",
  "amount": 150
}

Advantages of Event-Driven Architecture

Loose Coupling

Services do not depend on each other.

High Scalability

Consumers scale independently.

Better Fault Isolation and Independent

Failure in one service does not break the entire system.

Real-Time Processing

Events trigger instant workflows.

When to Use Event-Driven Architecture

Event Driven Architecture is ideal for:

Conclusion

Event-driven architecture has become a core foundation of modern cloud-native application design. With Azure services such as Microsoft Azure Event Grid, Microsoft Azure Service Bus, Event Hubs, and Azure Functions, developers can build systems that are highly scalable, resilient, and capable of responding to real-time business events. For .NET developers, combining these services with ASP.NET Core and serverless functions makes it easier to create robust, loosely coupled, and efficient event-driven workflows.

As more organizations adopt microservices and distributed architectures, understanding event-driven design patterns is no longer optional—it is becoming an essential skill for modern software architects and developers.

In this article, we explored what Azure event services are, why they matter in modern application development, reviewed the major types of event services, and briefly demonstrated practical use cases with real-world implementation examples.

Sample GitHub repo can be found here.