Azure Event Grid: Event-Driven Architecture Made Simple

Event Grid is Azure’s fully managed event routing service. Publish events from any source, subscribe from any handler—at massive scale.

Core Concepts

• Events: What happened (small, lightweight)
• Publishers: Where events come from
• Topics: Endpoints for sending events
• Subscriptions: Routes events to handlers
• Handlers: Where events go (Functions, Logic Apps, webhooks)

Event Schema

{
    "id": "unique-event-id",
    "eventType": "MyApp.Orders.OrderPlaced",
    "subject": "/orders/12345",
    "eventTime": "2020-10-17T10:30:00Z",
    "data": {
        "orderId": "12345",
        "customerId": "cust-789",
        "total": 99.99
    },
    "dataVersion": "1.0"
}

Creating a Custom Topic

# Create topic
az eventgrid topic create \
    --name myapp-events \
    --location eastus \
    --resource-group myRG

# Get endpoint and key
az eventgrid topic show --name myapp-events --resource-group myRG --query endpoint
az eventgrid topic key list --name myapp-events --resource-group myRG --query key1

Publishing Events

using Azure.Messaging.EventGrid;

var client = new EventGridPublisherClient(
    new Uri("https://myapp-events.eastus-1.eventgrid.azure.net/api/events"),
    new AzureKeyCredential("your-key")
);

var events = new List<EventGridEvent>
{
    new EventGridEvent(
        subject: "/orders/12345",
        eventType: "MyApp.Orders.OrderPlaced",
        dataVersion: "1.0",
        data: new { orderId = "12345", total = 99.99 }
    )
};

await client.SendEventsAsync(events);

Creating Subscriptions

Azure Function Handler

az eventgrid event-subscription create \
    --name order-processor \
    --source-resource-id /subscriptions/{sub}/resourceGroups/myRG/providers/Microsoft.EventGrid/topics/myapp-events \
    --endpoint /subscriptions/{sub}/resourceGroups/myRG/providers/Microsoft.Web/sites/myfunc/functions/ProcessOrder \
    --endpoint-type azurefunction

Webhook Handler

az eventgrid event-subscription create \
    --name order-webhook \
    --source-resource-id /subscriptions/{sub}/resourceGroups/myRG/providers/Microsoft.EventGrid/topics/myapp-events \
    --endpoint https://myapi.com/webhooks/eventgrid \
    --endpoint-type webhook

Azure Function Handler

[FunctionName("ProcessOrder")]
public static async Task Run(
    [EventGridTrigger] EventGridEvent eventGridEvent,
    ILogger log)
{
    log.LogInformation($"Event type: {eventGridEvent.EventType}");
    log.LogInformation($"Subject: {eventGridEvent.Subject}");
    log.LogInformation($"Data: {eventGridEvent.Data}");

    var orderData = eventGridEvent.Data.ToObjectFromJson<OrderData>();
    // Process order...
}

Event Filtering

# Filter by event type
az eventgrid event-subscription create \
    --name filtered-sub \
    --source-resource-id ... \
    --endpoint ... \
    --included-event-types MyApp.Orders.OrderPlaced MyApp.Orders.OrderShipped

# Advanced filtering
az eventgrid event-subscription create \
    --name advanced-sub \
    --source-resource-id ... \
    --endpoint ... \
    --advanced-filter data.total NumberGreaterThan 100

System Topics (Azure Service Events)

# Subscribe to Blob Storage events
az eventgrid event-subscription create \
    --name blob-events \
    --source-resource-id /subscriptions/{sub}/resourceGroups/myRG/providers/Microsoft.Storage/storageAccounts/mystorageaccount \
    --endpoint /subscriptions/{sub}/resourceGroups/myRG/providers/Microsoft.Web/sites/myfunc/functions/ProcessBlob \
    --endpoint-type azurefunction \
    --included-event-types Microsoft.Storage.BlobCreated

Dead Letter and Retry

# Configure dead letter destination
az eventgrid event-subscription update \
    --name my-sub \
    --source-resource-id ... \
    --deadletter-endpoint /subscriptions/{sub}/resourceGroups/myRG/providers/Microsoft.Storage/storageAccounts/mystorageaccount/blobServices/default/containers/deadletter

Event Grid enables reactive, event-driven architectures at scale.