Azure Functions Event Hub Triggers

This document explains how to use the Event Hub trigger for Azure Functions. The Event Hub trigger allows your Azure Functions to react to events published to an Azure Event Hubs instance.

Overview

The Event Hub trigger integrates seamlessly with Azure Event Hubs, a highly scalable data streaming platform and event ingestion service. When events are sent to an Event Hub, the trigger can automatically invoke your function to process these events.

When to Use an Event Hub Trigger

• Processing real-time data streams from IoT devices.
• Ingesting and processing clickstream data from web applications.
• Reacting to telemetry data from services.
• Building event-driven architectures where Event Hubs acts as a central message bus.

Configuration

The Event Hub trigger is configured using attributes in your function code or through the function.json file.

C# Example (using Attributes)

C#
using Microsoft.Azure.WebJobs;
using Microsoft.Extensions.Logging;
using Azure.Messaging.EventHubs;
using System.Collections.Generic;
using System.Threading.Tasks;

public static class EventHubProcessor
{
    [FunctionName("EventHubTriggerFunction")]
    public static async Task Run(
        [EventHubTrigger("my-event-hub", Connection = "EventHubConnectionAppSetting")] EventData[] events,
        ILogger log)
    {
        log.LogInformation($"C# Event Hub trigger function processed a batch of {events.Length} events.");

        foreach (EventData eventData in events)
        {
            log.LogInformation($"Message Body: {System.Text.Encoding.UTF8.GetString(eventData.EventBody.ToArray())}");
            log.LogInformation($"Enqueued Time Utc: {eventData.EnqueuedTime}");
            log.LogInformation($"Partition Key: {eventData.PartitionKey}");
        }

        log.LogInformation("Finished processing events.");
    }
}
        

JavaScript Example (using function.json)

In your function.json file for a JavaScript function:

JSON
{
  "bindings": [
    {
      "name": "eventHubMessages",
      "type": "eventHubTrigger",
      "direction": "in",
      "eventHubName": "my-event-hub",
      "connection": "EventHubConnectionAppSetting",
      "consumerGroup": "$Default"
    }
  ],
  "scriptFile": "index.js"
}
        

And in your index.js file:

JavaScript
module.exports = async function (context, eventHubMessages) {
    context.log(`JavaScript Event Hub trigger function processed a batch of ${eventHubMessages.length} events.`);

    for (const eventData of eventHubMessages) {
        context.log(`Message Body: ${eventData.body}`);
        context.log(`Enqueued Time Utc: ${eventData.enqueuedTimeUtc}`);
        context.log(`Partition Key: ${eventData.partitionKey}`);
    }

    context.log("Finished processing events.");
};
        

Key Configuration Properties

Property	Description	Required
eventHubName	The name of the Event Hub to monitor.	Yes
connection	The name of an App Setting that contains the Event Hubs connection string.	Yes
consumerGroup	The consumer group that the function will join. Defaults to $Default.	No
accessRights	The access rights required for the trigger. Defaults to Listen.	No

Batch Processing

The Event Hub trigger processes events in batches. The size of the batch can be configured. This allows for more efficient processing of large volumes of events.

Configuring Batch Size

You can configure the batch size using the IsBatched and MaxBatchSize properties in function.json or attributes in C#.

JSON
{
  "bindings": [
    {
      "name": "eventHubMessages",
      "type": "eventHubTrigger",
      "direction": "in",
      "eventHubName": "my-event-hub",
      "connection": "EventHubConnectionAppSetting",
      "consumerGroup": "$Default",
      "isBatched": true,
      "maxBatchSize": 100
    }
  ],
  "scriptFile": "index.js"
}
        

C#
[EventHubTrigger("my-event-hub", Connection = "EventHubConnectionAppSetting", IsBatched = true, MaxBatchSize = 100)]
public static async Task Run(EventData[] events, ILogger log) { ... }
        

Error Handling and Retries

Azure Functions provides built-in mechanisms for handling errors and retrying failed operations. The Event Hub trigger leverages these by default. If an error occurs during function execution, the batch of events might be retried.

Consider implementing idempotent logic within your function to safely handle potential retries without unintended side effects.

Checkpointing

The Event Hub trigger automatically manages checkpoints to keep track of which events have been successfully processed. This ensures that events are not lost and that processing can resume from the last checkpoint in case of failures or restarts.

The checkpointing mechanism is typically managed by the Azure Functions runtime based on the consumer group and Event Hub configuration.

Best Practices

• Use a separate consumer group for your Azure Function to avoid conflicts with other consumers of the same Event Hub.
• Handle large batches efficiently by processing events asynchronously or in parallel within your function.
• Implement robust error handling and logging to diagnose and resolve issues quickly.
• Ensure idempotency in your function logic to handle potential duplicate event processing due to retries.
• Monitor your function's performance and throughput to ensure it can keep up with the event volume.

For more advanced scenarios and detailed API references, please refer to the official Azure Functions documentation.