Azure Functions Event Grid Trigger

The Event Grid trigger allows you to run an Azure Function in response to events published by Azure Event Grid or custom event sources. This is a powerful way to build event-driven applications and integrate with various Azure services.

Overview

Event Grid is a fully managed event routing service that enables you to easily build applications with event-based architectures. When an event occurs in an Azure service or a custom application, Event Grid can route that event to your Azure Function. The function is then invoked with the event data, allowing you to process it.

How it Works

To use the Event Grid trigger, you need to:

1. Create an Event Grid Subscription: You create a subscription to an event source (e.g., a Storage Account, a custom topic). This subscription specifies the events you're interested in and the endpoint where Event Grid should send those events.
2. Configure the Azure Function: You create an Azure Function with an Event Grid trigger. This function will listen for events from the configured Event Grid subscription.
3. Event Delivery: When an event matching the subscription criteria is published, Event Grid sends an HTTP POST request to your Azure Function's endpoint with the event payload.
4. Function Execution: Your Azure Function is triggered and executes its code to process the event data.

Creating an Event Grid Triggered Function

Using Azure Portal

1. Navigate to your Azure Function App.
2. Click on "Functions" in the left-hand menu.
3. Click "+ Create".
4. Select "Azure Event Grid Trigger" from the template list.
5. Provide a Function name.
6. In the "Event subscription" section, click "Create Event Subscription".
7. Configure the event subscription details:
   • Event Subscription Name: A unique name for your subscription.
   • Event Types: Select the specific events you want to trigger your function (e.g., Microsoft.Storage.BlobCreated).
   • Topic Type: Choose the type of topic (e.g., Azure Subscriptions, Resource Groups, Storage Accounts).
   • Azure Subscription / Resource Group / Storage Account: Select the relevant resource.
   • Endpoint Type: Select "Azure Function".
   • Endpoint: This will be automatically populated with your function's URL.
8. Click "OK" to create the event subscription.
9. Click "Create" to create your function.

Using Code (Example: C#)

Here's a simple example of an Event Grid triggered function in C#:

using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.EventGrid;
using Microsoft.Extensions.Logging;
using Azure.Messaging.EventGrid.Models; // Ensure you have the correct namespace

namespace EventGridTriggerFunction
{
    public static class EventGridProcessor
    {
        [FunctionName("EventGridProcessor")]
        public static void Run([EventGridTrigger] EventGridEvent eventGridEvent, ILogger log)
        {
            log.LogInformation($"Received Event Grid event: {eventGridEvent.EventType}");
            log.LogInformation($"Subject: {eventGridEvent.Subject}");
            log.LogInformation($"Data: {eventGridEvent.Data}");
            log.LogInformation($"Topic: {eventGridEvent.Topic}");
            log.LogInformation($"Event Time: {eventGridEvent.EventTime}");

            // Process the event data here. The structure of eventGridEvent.Data
            // depends on the event type. You might need to deserialize it.
            // For example, for blob creation events:
            // var blobData = eventGridEvent.Data.ToObjectFromJson<StorageBlobCreatedEventData>();
            // log.LogInformation($"Blob path: {blobData.Url}");
        }
    }
}
            

Function.json Configuration (for other languages)

For languages like JavaScript, Python, or PowerShell, the binding configuration is defined in function.json:

{
  "scriptFile": "__init__.py", // Or your script file
  "bindings": [
    {
      "name": "eventGridEvent",
      "type": "eventGridTrigger",
      "direction": "in",
      "eventName": "Microsoft.Storage.BlobCreated", // Optional: Filter by event name
      "topicEndpoint": "YOUR_TOPIC_ENDPOINT", // Optional: Filter by topic endpoint
      "subjectPrefix": "YOUR_SUBJECT_PREFIX" // Optional: Filter by subject prefix
    }
  ]
}
            

Event Grid Event Schema

The EventGridEvent object contains information about the event. Key properties include:

• id: Unique ID for the event.
• subject: Subject of the event (e.g., the resource that produced the event).
• data: The event payload. The structure varies based on the event type.
• eventType: The type of event that occurred (e.g., Microsoft.Storage.BlobCreated).
• eventTime: The time the event occurred.
• topic: The resource associated with the event.
• dataVersion: The schema version of the data property.
• metadataVersion: The schema version of the event metadata.

Key Concepts

• Event Source: The service or application that publishes events.
• Event Subscription: A configuration that defines which events from a source should be delivered to a specific endpoint.
• Event Handler: The application that receives and processes events (in this case, your Azure Function).
• Topics: Event Grid topics are the communication channels through which event publishers send events.

Use Cases

• Responding to file uploads in Blob Storage.
• Processing changes in Azure Cosmos DB documents.
• Notifying systems when a virtual machine is started or stopped.
• Building custom workflows triggered by custom applications.