Event-Driven Architecture: Using Azure Event Grid for Decoupled Microservices

How to build reactive, scalable systems by shifting from orchestration to event-based choreography.

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The limitations of synchronous, request-response architectures are becoming more apparent as we scale. When Service A must wait for Service B to finish before it can respond to a user, we create a chain of dependency that impacts latency and reliability.

To solve this, we are moving toward Event-Driven Architecture (EDA). By using Azure Event Grid, we can shift from a “command” mindset to an “event” mindset, allowing our microservices to become truly decoupled and reactive.

The Problem: The “Strong Coupling” Trap

In traditional architectures, services are often tightly coupled via REST or gRPC calls. If the downstream service is down or slow, the upstream service fails too. This “distributed monolith” approach makes scaling difficult and deployments risky.

We need a way for services to announce that “something happened” without needing to know who is listening or how they will react.

The Solution: Event-Based Choreography

Azure Event Grid is a fully managed, HTTP-based event routing service. It uses a Publish-Subscribe (Pub/Sub) model that allows you to build systems based on choreography rather than strict orchestration.

Key Concepts in Event Grid:

  • Events: What happened (e.g., “FileUploaded”, “OrderPlaced”).
  • Publishers: Where the event took place (Azure Storage, Custom Apps).
  • Topics: The endpoint where publishers send events.
  • Event Subscriptions: The routing mechanism that decides which events go to which handlers.
  • Event Handlers: The app or service reacting to the event (Azure Functions, Logic Apps, Webhooks).

Architecture: Orchestration vs. Choreography

As a Solution Architect, I often explain the difference using a “Director” vs. a “Dancer” analogy:

  • Orchestration (The Director): A central service tells others exactly what to do and in what order. If the director stops, the show stops.
  • Choreography (The Dancers): Each service reacts to events in the environment. When an “OrderCreated” event is fired, the Inventory service updates stock, and the Email service sends a confirmation—independently and simultaneously.

Technical Insight: Why Event Grid?

Why choose Event Grid over Service Bus or Event Hubs? It comes down to intent:

  • Event Grid: Best for “Discrete Events” (actions like a state change). It is highly scalable and supports near real-time routing with a push-push model.
  • Service Bus: Best for “Messages” (commands that require high reliability and transactional support).
  • Event Hubs: Best for “Telemetry Data” (streaming millions of events per second).

By using Event Grid, we reduce the Cognitive Load on our developers. They no longer need to write complex retry logic or manage connection strings for every downstream service; they simply emit an event and let the platform handle the distribution.

Getting Started on Azure

  1. Define your Custom Topic: Create a topic in the Azure Portal or via CLI.
  2. Schema Selection: Use the CloudEvents 1.0 standard for better cross-platform compatibility.
  3. Filter Logic: Use Event Grid’s built-in filtering to ensure subscribers only receive the specific events they care about (e.g., filter by eventType).

Deep Dive: Reference Material & Implementation Links

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