Receiving Events from Azure Event Hubs

Once events are sent to an Azure Event Hub, you'll need a mechanism to receive and process them. Azure Event Hubs supports several client libraries and integration patterns to facilitate this.

Using the Event Hubs SDKs

The recommended way to receive events is by using the official Azure Event Hubs SDKs. These libraries provide robust, high-level abstractions for connecting to your Event Hub, managing checkpoints, and processing events in a fault-tolerant manner.

C# Example (Azure.Messaging.EventHubs)

This example demonstrates using the Azure SDK for .NET to receive events.

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

public class EventProcessor
{
    private const string connectionString = "";
    private const string eventHubName = "";
    private const string consumerGroup = "$Default"; // Or your custom consumer group

    public static async Task Main(string[] args)
    {
        await using var client = new EventHubConsumerClient(
            EventHubConsumerClient.DefaultConsumerGroupName,
            connectionString,
            eventHubName);

        Console.WriteLine("Starting to read events...");

        await foreach (PartitionEvent partitionEvent in client.ReadEventsAsync())
        {
            try
            {
                string messageBody = Encoding.UTF8.GetString(partitionEvent.Data.EventBody.ToArray());
                Console.WriteLine($"Received event: {messageBody} from partition {partitionEvent.Partition.Id}");

                // In a real application, you would checkpoint here to mark events as processed.
                // await client.UpdateCheckpointAsync(partitionEvent);
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Error processing event: {ex.Message}");
            }
        }
    }
}
                

Using Azure Functions

Azure Functions provide a serverless compute option that integrates seamlessly with Event Hubs. The Event Hub trigger allows your function to be invoked automatically when new events arrive.

Example Azure Function (in TypeScript)

This is a conceptual representation of an Azure Function triggered by Event Hubs.

import { AzureFunction, Context, EventHubTrigger } from "@azure/functions";

const eventHubTriggerHandler: AzureFunction = async function (
    context: Context,
    events: EventData[]
): Promise {
    context.log(`JavaScript Event Hub trigger function processed ${events.length} events`);

    for (const event of events) {
        const message = Buffer.from(event.body).toString('utf-8');
        context.log(`Received message: ${message} from partition ${event.properties.partitionId}`);
        // Process the message...
    }
};

export default eventHubTriggerHandler;
                

Using Event Hubs Capture

Event Hubs Capture is a built-in feature that automatically and continuously archives events from an Event Hub to an Azure Blob Storage account or Azure Data Lake Storage Gen2. This is ideal for batch processing or for retaining historical data.

Configure Capture

1. Navigate to your Event Hub in the Azure portal.
2. In the left-hand menu, select "Features" > "Capture".
3. Enable Capture.
4. Configure the destination storage account and container.
5. Set the capture interval (e.g., every 1 minute or 1 MB of data).

Checkpointing

To ensure reliable event processing and prevent duplicate processing or missed events in case of failures, it's crucial to implement checkpointing. Checkpointing involves recording the offset and sequence number of the last successfully processed event for a given partition and consumer group. The Event Hubs SDKs and Azure Functions provide mechanisms for managing checkpoints.