Azure Event Hubs Documentation

Processing Events from Azure Event Hubs

Efficiently processing events from Azure Event Hubs is crucial for building responsive and scalable event-driven applications. This guide covers key strategies and considerations for developing robust event processors.

Understanding Event Processing Models

Azure Event Hubs offers several ways to consume and process events:

Using the Event Hubs SDK for Event Processing

The Event Hubs SDK provides a powerful and flexible way to build custom event processors. The core component is the Event Processor Host (EPH) (or similar abstractions in newer SDKs) which manages the complexities of:

Key Concepts in SDK-based Processing:

Example (Conceptual C# using older EPH model):


using Azure.Messaging.EventHubs;
using Azure.Messaging.EventHubs.Consumer;
using Azure.Storage.Blobs;
using System;
using System.Text;
using System.Threading.Tasks;

public class EventProcessor
{
    private const string EventHubConnectionString = "YOUR_EVENT_HUB_CONNECTION_STRING";
    private const string ConsumerGroup = "$Default"; // Or your custom consumer group
    private const string BlobStorageConnectionString = "YOUR_BLOB_STORAGE_CONNECTION_STRING";
    private const string BlobContainerName = "eventhub-checkpoints";

    public static async Task RunProcessorAsync()
    {
        var consumerClient = new EventHubConsumerClient(
            EventHubConsumerClient.DefaultConsumerGroupName,
            EventHubConnectionString);

        var blobServiceClient = new BlobServiceClient(BlobStorageConnectionString);
        var blobContainerClient = blobServiceClient.GetBlobContainerClient(BlobContainerName);

        // This processor will continuously process events.
        // For a real-world scenario, you'd manage the lifecycle of the processor.
        await consumerClient.ReceiveAsync(ProcessEvents, ProcessError, TimeSpan.FromMinutes(1));
    }

    static async Task ProcessEvents(PartitionEvent partitionEvent)
    {
        try
        {
            Console.WriteLine($"Received event: Sequence Number {partitionEvent.Data.SequenceNumber}, Offset {partitionEvent.Data.Offset}");
            string messageBody = Encoding.UTF8.GetString(partitionEvent.Data.EventBody.ToArray());
            Console.WriteLine($"Message: {messageBody}");

            // Process your event here...
            // Example: Save to database, trigger another service, etc.

            // If processing is successful, record the checkpoint.
            // In a real app, you'd use an EventProcessorClient with checkpointing integrated.
            // This simplified example assumes manual checkpointing coordination.
            await Task.Delay(100); // Simulate processing time
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Error processing event: {ex.Message}");
            // Handle the error appropriately. Depending on the error, you might want to retry or log.
        }
    }

    static Task ProcessError(PartitionError partitionError)
    {
        Console.WriteLine($"Error in partition {partitionError.PartitionId}: {partitionError.Error.Message}");
        return Task.CompletedTask;
    }
}

Leveraging Azure Functions for Event Processing

Azure Functions provide a serverless and event-driven way to process Event Hubs. The Event Hubs trigger for Azure Functions automatically handles:

This significantly simplifies development, allowing you to focus on the business logic of processing each event.

Example (Conceptual C# Azure Function):


using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Azure.Messaging.EventHubs;
using Microsoft.Azure.WebJobs;
using Microsoft.Extensions.Logging;

public static class EventHubProcessorFunction
{
    [FunctionName("EventHubProcessor")]
    public static async Task Run(
        [EventHubTrigger("your-eventhub-name",
                         Connection = "EventHubConnectionString",
                         ConsumerGroup = "$Default")] EventData[] events,
        ILogger log)
    {
        var exceptions = new List<Exception>();

        foreach (EventData eventData in events)
        {
            try
            {
                log.LogInformation($"C# Event Hub trigger function processed a message: SequenceNumber:{eventData.SequenceNumber} PartitionKey:{eventData.PartitionKey}");
                string messageBody = Encoding.UTF8.GetString(eventData.EventBody.ToArray());
                log.LogInformation($"Message body: {messageBody}");

                // Process your event here...
                // Example: Save to database, call another API

                // Azure Functions runtime handles checkpointing automatically on successful execution.
                await Task.Delay(10); // Simulate processing
            }
            catch (Exception e)
            {
                // We need to keep track of exceptions to report them after the loop finishes.
                exceptions.Add(e);
            }
        }

        // If any exceptions were thrown, re-throw them to trigger a retry mechanism.
        if (exceptions.Count > 1)
        {
            throw new AggregateException(exceptions);
        }

        if (exceptions.Any())
        {
            throw exceptions.First();
        }
    }
}

Best Practices for Event Processing

Important: Always use the latest stable version of the Azure Event Hubs SDKs for your chosen programming language to benefit from the latest features, performance improvements, and security updates.