Azure Functions Documentation

Event Hubs Bindings for Azure Functions

Azure Functions provide robust integration with Azure Event Hubs, allowing you to build serverless event-driven applications that process high volumes of data. Event Hubs bindings enable your functions to act as either triggers or outputs for Event Hubs, simplifying the development of complex streaming scenarios.

Event Hubs Trigger

The Event Hubs trigger allows your function to be executed automatically when new events are available in an Event Hubs consumer group. This is the most common way to process incoming event streams.

Configuration

To configure an Event Hubs trigger, you define a binding in your function.json file or use attributes in your code.

Example (function.json):

{
  "scriptFile": "run.cs",
  "bindings": [
    {
      "name": "myEventHubTrigger",
      "type": "eventHubTrigger",
      "direction": "in",
      "connection": "EventHubConnection",
      "eventHubName": "myeventhub",
      "consumerGroup": "$Default"
    }
  ]
}

Parameters:

• name: The name of the parameter in your function code that will receive the event data.
• type: Must be eventHubTrigger.
• direction: Must be in for a trigger.
• connection: The name of an application setting that contains the Event Hubs connection string.
• eventHubName: The name of the Event Hub to monitor.
• consumerGroup: The consumer group for the Event Hub. Defaults to $Default.

Event Hubs Output Binding

The Event Hubs output binding allows your function to send data to an Azure Event Hub. This is useful for scenarios where your function processes incoming data and then forwards or enriches it to another Event Hub for further processing or archival.

Configuration

Similar to triggers, output bindings are defined in function.json or using attributes.

Example (function.json):

{
  "scriptFile": "run.cs",
  "bindings": [
    {
      "name": "myEventHubTrigger",
      "type": "eventHubTrigger",
      "direction": "in",
      "connection": "EventHubConnection",
      "eventHubName": "myeventhub"
    },
    {
      "name": "outputEventHub",
      "type": "eventHub",
      "direction": "out",
      "connection": "EventHubConnection",
      "eventHubName": "processedhub"
    }
  ]
}

Parameters:

• name: The name of the parameter in your function code used to send data.
• type: Must be eventHub.
• direction: Must be out for an output binding.
• connection: The name of an application setting that contains the Event Hubs connection string.
• eventHubName: The name of the Event Hub to send data to.

Batching and Checkpointing

Event Hubs triggers process events in batches for efficiency. Functions automatically manage checkpointing to keep track of processed events, ensuring reliable message delivery and preventing duplicate processing.

Code Examples

Here's a simplified C# example demonstrating both a trigger and an output binding:

// Function.cs
using System.Collections.Generic;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Host;
using Microsoft.Azure.EventHubs;
using Microsoft.Extensions.Logging;

public static class EventHubProcessor
{
    [FunctionName("EventHubProcessor")]
    public static void Run(
        [EventHubTrigger("myeventhub", Connection = "EventHubConnection")] EventData[] events,
        [EventHub("processedhub", Connection = "EventHubConnection")] IAsyncCollector outputEventHub,
        ILogger log)
    {
        log.LogInformation($"C# Event Hub trigger function processed a batch of {events.Length} events.");

        foreach (EventData eventData in events)
        {
            string messageBody = System.Text.Encoding.UTF8.GetString(eventData.Body.Array);
            log.LogInformation($"Event Body: {messageBody}");

            // Example: Enrich or transform the message
            string processedMessage = $"Processed: {messageBody}";

            // Send the processed message to another Event Hub
            outputEventHub.AddAsync(processedMessage).GetAwaiter().GetResult();
            log.LogInformation($"Sent to processedhub: {processedMessage}");
        }
    }
}

Best Practices

• Use dedicated consumer groups for each function processing the same Event Hub.
• Secure your connection strings using Azure Key Vault or application settings.
• Implement robust error handling and logging for event processing.
• Consider the batch size and frequency of invocations for performance tuning.