Event Grid Trigger¶

Note: This recipe covers Event Grid integration for future extensibility beyond HTTP triggers. The most common pattern shown here is an HTTP trigger that publishes events to Event Grid, and an Event Grid trigger that consumes them.

Overview¶

Azure Event Grid is a fully managed event routing service that uses a publish-subscribe model. It is ideal for reactive, event-driven architectures where you need to fan-out notifications to multiple subscribers or decouple producers from consumers.

Common use cases with Azure Functions:

HTTP → Event Grid: An HTTP API publishes domain events (order created, user registered) to Event Grid
Event Grid → Function: A function subscribes to events from Azure services (blob created, resource changed) or custom topics
Cross-service communication: Decouple microservices using events instead of direct HTTP calls

Architecture¶

flowchart LR
    SRC[Event Source] --> EG[Event Grid Topic or System Topic]
    EG --> FA[Function App]
    FA --> DOWN[Downstream Service]

Solid arrows show runtime data/event flow. Dashed arrows show identity and authentication.

Prerequisites¶

Event Grid bindings are included in the default extension bundle:

{
  "version": "2.0",
  "extensionBundle": {
    "id": "Microsoft.Azure.Functions.ExtensionBundle",
    "version": "[4.*, 5.0.0)"
  }
}

Create an Event Grid topic for custom events:

# Create an Event Grid topic
az eventgrid topic create \
  --name your-topic \
  --resource-group your-rg \
  --location eastus

# Get the topic endpoint and key
az eventgrid topic show \
  --name your-topic \
  --resource-group your-rg \
  --query "endpoint" --output tsv

az eventgrid topic key list \
  --name your-topic \
  --resource-group your-rg \
  --query "key1" --output tsv

Event Grid Output: Publish Events from HTTP Trigger¶

Use the Event Grid output binding to publish events when an HTTP request is received:

import azure.functions as func
import json
import uuid
from datetime import datetime, timezone

bp = func.Blueprint()

@bp.route(route="orders", methods=["POST"])
@bp.event_grid_output(
    arg_name="outputEvent",
    topic_endpoint_uri="EVENT_GRID_TOPIC_ENDPOINT",
    topic_key_setting="EVENT_GRID_TOPIC_KEY"
)
def create_order(req: func.HttpRequest, outputEvent: func.Out[func.EventGridOutputEvent]) -> func.HttpResponse:
    """Create an order and publish an OrderCreated event."""
    try:
        body = req.get_json()
    except ValueError:
        return func.HttpResponse(
            json.dumps({"error": "Invalid JSON body"}),
            mimetype="application/json",
            status_code=400
        )

    order_id = str(uuid.uuid4())

    # Publish the event to Event Grid
    event = func.EventGridOutputEvent(
        id=str(uuid.uuid4()),
        data={"order_id": order_id, "items": body.get("items", [])},
        subject=f"orders/{order_id}",
        event_type="Order.Created",
        data_version="1.0"
    )
    outputEvent.set(event)

    return func.HttpResponse(
        json.dumps({"order_id": order_id, "status": "created", "event_published": True}),
        mimetype="application/json",
        status_code=201
    )

Configure the app settings:

az functionapp config appsettings set \
  --name your-func \
  --resource-group your-rg \
  --settings \
    "EVENT_GRID_TOPIC_ENDPOINT=https://your-topic.eastus-1.eventgrid.azure.net/api/events" \
    "EVENT_GRID_TOPIC_KEY=<your-topic-key>"