Azure Functions Event Hub Bindings

Azure Functions provide powerful and flexible bindings for integrating with Azure services. Event Hubs is a highly scalable data streaming platform and event ingestion service that can handle millions of events per second. This page details how to use Event Hubs bindings with Azure Functions.

Input Bindings (Triggers)

Event Hubs can be used as a trigger for your Azure Functions. This means your function will be executed automatically when new events are available in an Event Hubs consumer group.

Configuration

To use an Event Hubs trigger, you'll typically configure your function's function.json or use attributes in code (for language-specific implementations).

Example function.json for a C# Event Hubs trigger:

json

{
  "scriptFile": "__init__.py",
  "bindings": [
    {
      "name": "eventHubMessages",
      "type": "eventHubTrigger",
      "direction": "in",
      "eventHubName": "myEventHub",
      "consumerGroup": "$Default",
      "connection": "EventHubConnectionString"
    }
  ]
}

Parameters:

name: The name of the parameter in your function code that will receive the event data.
type: Set to eventHubTrigger.
direction: Set to in.
eventHubName: The name of the Event Hub to monitor.
consumerGroup: The consumer group to use. $Default is often used.
connection: The name of an app setting that contains the Event Hubs connection string.

Handling Batched Events

Event Hubs triggers often receive events in batches. Your function code needs to be able to process these batches efficiently.

Example Python function processing batched events:

python

import logging
import json

import azure.functions as func

def main(eventHubMessages: [func.EventHubEvent]):
    logging.info(f"Python EventHub trigger function processed {len(eventHubMessages)} events.")

    for message in eventHubMessages:
        try:
            event_data = message.get_body().decode('utf-8')
            logging.info(f"EnqueuedTimeUtc: {message.enqueued_time_utc}")
            logging.info(f"SequenceNumber: {message.sequence_number}")
            logging.info(f"Offset: {message.offset}")
            logging.info(f"Body: {event_data}")

            # Process the event data, e.g., parse JSON
            data = json.loads(event_data)
            logging.info(f"Processed data: {data.get('key')}")

        except Exception as e:
            logging.error(f"Error processing event: {e}")
            # Consider error handling strategies like dead-lettering or retries
            # For simple logging, you might just log the error and continue.
            # More robust handling depends on your application's requirements.

Output Bindings

Azure Functions can also send data to Event Hubs using an output binding. This allows your function to act as a producer for an Event Hub.

Configuration

Similar to triggers, output bindings are configured in function.json or via attributes.

Example function.json for a C# Event Hubs output binding:

json

{
  "scriptFile": "MyOutputFunction.cs",
  "bindings": [
    {
      "name": "outputEvent",
      "type": "eventHub",
      "direction": "out",
      "eventHubName": "outputEventHub",
      "connection": "EventHubConnectionString"
    }
  ]
}

Parameters:

name: The name of the parameter in your function code that will be used to send events.
type: Set to eventHub.
direction: Set to out.
eventHubName: The name of the Event Hub to send events to.
connection: The name of an app setting that contains the Event Hubs connection string.

Example C# function using an Event Hubs output binding:

csharp

using Microsoft.Azure.WebJobs;
using Microsoft.Extensions.Logging;
using System;

public static class MyOutputFunction
{
    [FunctionName("SendToEventHub")]
    public static void Run(
        [TimerTrigger("0 */5 * * * *")] TimerInfo myTimer, // Example: runs every 5 minutes
        [EventHub("outputEventHub", Connection = "EventHubConnectionString")] out string outputEvent,
        ILogger log)
    {
        log.LogInformation($"C# Timer trigger function executed at: {DateTime.Now}");

        string message = $"Hello from Azure Functions at {DateTime.Now}";
        outputEvent = message; // Assign the string to the output binding parameter

        log.LogInformation($"Sent message to Event Hub: {message}");
    }
}

Best Practices

Consumer Groups: Use dedicated consumer groups for different applications or instances to avoid processing the same events multiple times.
Error Handling: Implement robust error handling, including retries and dead-lettering mechanisms, for processing events.
Batch Processing: Design your functions to efficiently handle batches of events for better performance.
Connection Strings: Store connection strings securely in application settings (e.g., Azure App Configuration or Application Settings in Azure Functions).
Monitoring: Monitor your Event Hubs and Azure Functions for latency, throughput, and error rates.

Azure Functions Documentation