Building Event-Driven Microservices with Azure Event Grid

Introduction

Modern applications often consist of multiple microservices that need to communicate with each other. In traditional architectures, one service directly calls another using HTTP APIs. While this approach is simple, it creates tight coupling between services, making applications harder to scale and maintain.

An event-driven architecture solves this problem by allowing services to communicate through events instead of direct calls. When something important happens, such as a new order being placed or a file being uploaded, an event is published. Other services that are interested in that event receive it and perform their own tasks independently.

Azure Event Grid is a fully managed event routing service that makes it easy to build scalable, reliable, and loosely coupled event-driven applications.

In this article, you'll learn how Azure Event Grid works, how it fits into a microservices architecture, and the best practices for building event-driven solutions.

What Is Azure Event Grid?

Azure Event Grid is a managed event routing service that delivers events from publishers to subscribers.

Instead of sending requests directly between services, applications publish events to Event Grid, which then routes those events to the appropriate subscribers.

This decouples services and allows them to evolve independently.

Common event sources include:

Azure Storage
Azure Functions
Event Hubs
Custom applications
Azure Resource Manager
IoT services

Applications can also publish their own custom events.

Why Use Event-Driven Architecture?

In a traditional application:

Order Service calls Inventory Service.
Inventory Service calls Billing Service.
Billing Service calls Notification Service.

Each service depends on the next one.

With an event-driven approach:

Order Service publishes an OrderCreated event.
Inventory Service updates stock.
Billing Service creates an invoice.
Notification Service sends an email.
Analytics Service records the transaction.

Each service operates independently, improving flexibility and resilience.

Publish a Custom Event

Applications can publish custom events to Azure Event Grid.

Example:

var eventData = new
{
    OrderId = 1001,
    Customer = "John Doe",
    Total = 499.99
};

The published event contains the information that subscribers need to process their own business logic.

Subscribe to Events

Multiple services can subscribe to the same event.

For example:

Event	Subscriber
OrderCreated	Inventory Service
OrderCreated	Billing Service
OrderCreated	Notification Service
OrderCreated	Analytics Service

Each subscriber processes the event independently without affecting the others.

Event Flow

A typical event-driven workflow looks like this:

A customer places an order.
The Order Service saves the order.
An OrderCreated event is published.
Azure Event Grid receives the event.
Event Grid routes the event to all subscribers.
Each service processes the event independently.

This architecture eliminates direct dependencies between services.

Filtering Events

Not every subscriber needs every event.

Azure Event Grid supports event filtering so that subscribers receive only relevant events.

For example:

Billing Service processes payment events.
Inventory Service processes stock events.
Notification Service processes email events.

Filtering reduces unnecessary processing and improves efficiency.

Retry and Reliability

Temporary failures can occur because of:

Network issues
Service outages
High server load

Azure Event Grid automatically retries event delivery for transient failures.

Applications should still be designed to handle duplicate event deliveries safely by implementing idempotent processing where appropriate.

Real-World Example

Imagine an online shopping platform.

When a customer uploads a product image:

The Storage Service publishes a BlobCreated event.
An Image Processing Service resizes the image.
A Content Moderation Service scans the image.
A Search Service updates its index.
A Notification Service informs the seller that processing is complete.

Each service performs its task independently without requiring changes to the upload service.

Monitor Event Processing

Monitoring helps ensure that events are delivered and processed successfully.

Useful metrics include:

Published events
Successful deliveries
Failed deliveries
Retry attempts
Processing latency
Dead-letter events

Regular monitoring helps identify issues before they affect users.

Best Practices

When building event-driven microservices with Azure Event Grid, follow these recommendations:

Design services to be loosely coupled and independently deployable.
Publish meaningful business events instead of implementation-specific events.
Keep event payloads small and include only the necessary data.
Use event filtering to reduce unnecessary processing.
Design subscribers to handle duplicate event deliveries safely.
Monitor delivery failures and configure dead-letter destinations where appropriate.
Secure event publishing and subscriptions using Azure authentication and authorization features.
Test event workflows under realistic production loads.

Conclusion

Azure Event Grid simplifies the development of event-driven microservices by providing a scalable and reliable way to route events between services. Instead of creating tightly coupled systems with direct service-to-service communication, applications can publish events that multiple subscribers process independently.

By following best practices such as publishing meaningful events, implementing idempotent processing, monitoring event delivery, and securing event endpoints, you can build resilient, scalable, and maintainable microservice architectures that adapt easily as your applications grow.