2.1.4. Implement Azure Event Grid

First Principle: Azure Event Grid delivers real-time event routing, enabling loosely coupled, reactive architectures. Its core purpose is to decouple event producers from consumers, allowing independent scaling and rapid evolution by reliably delivering events without requiring direct knowledge of consumers.

What It Is: Azure Event Grid is a fully managed event routing service that enables applications and services to react to events in real time, using a publish-subscribe model. It decouples event producers from event consumers, allowing scalable, loosely coupled, and reactive architectures.

Visual: "Azure Event Grid Event Routing"

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Core Components:

• "Events": Represent what happened, such as a blob being created or a resource being deleted. Each event contains data describing the occurrence.
• "Event Sources": The origin of events. These can be Azure services (e.g., Storage Accounts, Resource Groups), or custom applications that emit events.
• "Topics": Endpoints where event sources send events. "System topics" are built-in for Azure services (e.g., Azure Storage Events); "custom topics" are created for your own applications.
• "Event Handlers": Destinations that process events, such as Azure Functions, Logic Apps, Azure Automation, or webhooks. They act on the event data.
• "Event Subscriptions": Define which events from a "topic" are delivered to which "event handler". "Subscriptions" can include "filters" to route only relevant events.

Common Use Cases:

• "Serverless Application Architectures": Trigger Azure Functions or Logic Apps in response to cloud events (e.g., image resizing on blob upload), enabling scalable, "event-driven architectures".
• "Operational Automation": Automate responses to "resource changes" (e.g., auto-tagging resources on creation, alerting on security events from Azure Security Center).
• "Application Integration": Connect disparate systems by routing events between services, both within Azure and to external endpoints.

"Event Grid vs. Service Bus":

• "Event Grid" is designed for high-scale event routing, focusing on lightweight, reactive event distribution without guaranteed ordering or delivery. Ideal for quick, reactive responses to "what happened."
• "Azure Service Bus" is optimized for message brokering with guaranteed delivery and ordering, ideal for business processes and workflows where reliable message delivery and state are critical.

Scenario: You have an application that generates custom events (e.g., "OrderPlaced," "PaymentFailed"). You need to distribute these events to multiple, independent microservices (e.g., an order fulfillment service, a notification service, a logging service), ensuring loose coupling and real-time reaction.

Reflection Question: How does implementing Azure Event Grid, with its event routing capabilities (sources, topics, handlers, subscriptions), fundamentally enable applications and services to react to events in real time, supporting scalable, loosely coupled, and reactive architectures?

💡 Tip: Use Event Grid when you care about reacting to events (something happened), and the message payload is small. Use Service Bus when you need reliable message delivery (something to do), potentially with ordering or transactional guarantees.