Azure Event Hubs Developer's Guide

Introduction to Azure Event Hubs for Developers

Azure Event Hubs is a highly scalable data streaming platform and event ingestion service. It can capture millions of events per second so that you can build more applications and services. Event Hubs works with services like Azure Functions and Azure Databricks to power real-time analytics. This guide provides developers with the essential information needed to start building applications that send and receive events using Azure Event Hubs.

Getting Started

Before you can start sending or receiving events, you need to set up an Azure Event Hubs namespace and an event hub within that namespace. You will also need connection strings or other credentials to authenticate your applications.

Create an Event Hubs Namespace: Use the Azure portal, Azure CLI, or Azure SDKs to create a namespace.
Create an Event Hub: Within the namespace, create one or more event hubs.
Obtain Connection Strings: Find the shared access signature (SAS) keys or connection strings for your namespace or event hub.

For detailed steps, refer to the Azure Event Hubs Quickstart guide.

Sending Events

Applications send data to an event hub by producing events. Events are typically small messages containing business or telemetry data.

You can send events using the Azure Event Hubs SDKs for various languages (e.g., .NET, Java, Python, Node.js). Here's a conceptual example using Python:


from azure.eventhub import EventHubProducerClient, EventData

connection_str = "YOUR_EVENTHUBS_CONNECTION_STRING"
eventhub_name = "YOUR_EVENTHUB_NAME"

producer = EventHubProducerClient.from_connection_string(connection_str, eventhub_name=eventhub_name)

events = [
    EventData("First event data"),
    EventData("Second event data"),
    EventData("Third event data")
]

try:
    producer.send_batch(events)
    print("Sent events successfully")
except Exception as e:
    print(f"Error sending events: {e}")
finally:
    producer.close()

When sending events, consider:

Batching: Sending events in batches improves throughput and efficiency.
Partitioning: You can specify a partition key to ensure related events land in the same partition, maintaining order.
Content Type and Properties: Add metadata like content type, correlation IDs, and custom properties to your events.

Receiving Events

Applications consume data from an event hub by receiving events. Consumers belong to a consumer group, which is a view of an event hub. Each consumer within a consumer group reads from a specific set of partitions.

Here's a conceptual example using Python to receive events:


from azure.eventhub import EventHubConsumerClient, EventPosition

connection_str = "YOUR_EVENTHUBS_CONNECTION_STRING"
eventhub_name = "YOUR_EVENTHUB_NAME"
consumer_group = "$Default" # Or your custom consumer group

consumer = EventHubConsumerClient.from_connection_string(
    connection_str,
    consumer_group,
    eventhub_name=eventhub_name
)

def process_events(event):
    print(f"Received event: {event.body}")
    print(f"  Sequence number: {event.sequence_number}")
    print(f"  Offset: {event.offset}")

try:
    with consumer:
        consumer.subscribe(
            [eventhub_name],
            partition_id="0", # Subscribe to a specific partition or omit for all
            event_position=EventPosition("-1") # Start from the beginning, or use EventPosition.latest()
        )
        while True:
            for event in consumer.receive_batch(max_events=10): # Receive up to 10 events
                process_events(event)
except KeyboardInterrupt:
    print("Stopped receiving events.")

Key concepts for receiving events:

Consumer Groups: Isolate your application's view of events from other consumers.
Partition Ownership: Consumers in a consumer group coordinate to read from different partitions.
Checkpointing: Track your progress (offset) within a partition to resume reading from where you left off after a restart.

Partitioning

Event Hubs uses partitioning to allow parallel processing of event streams. An event hub can have up to 128 partitions. Each partition is an ordered, immutable sequence of events.

When you send an event, you can specify a partitionKey. Events with the same partition key are guaranteed to land in the same partition. If no partition key is specified, Event Hubs assigns the event to a partition.

Consumer Groups

A consumer group is a named view of an event hub. Each consumer group allows a separate instance of an application to read from the event hub independently. Event Hubs supports up to 20 concurrent consumer groups per event hub (this limit can be increased).

The $Default consumer group is created automatically. You can create custom consumer groups for specific processing needs.

Error Handling

Robust error handling is crucial for streaming applications. Common errors include network issues, authentication failures, and throttling exceptions.

Retry Mechanisms: Implement exponential backoff and retry logic for transient errors.
Dead-Lettering: For unrecoverable errors, consider sending problematic events to a dead-letter queue for later inspection.
Monitoring: Use Azure Monitor to track Event Hubs metrics like incoming/outgoing requests, errors, and latency.

Best Practices

Partitioning Strategy: Choose a partition key that distributes load evenly and maintains order for related events.
Batching: Maximize throughput by sending events in batches, but avoid excessively large batches that might cause timeouts.
Consumer Group Management: Use distinct consumer groups for different applications or processing pipelines.
Checkpointing: Implement reliable checkpointing to ensure data is processed without loss or duplication.
Security: Use managed identities or SAS tokens with limited scope for authentication.
Scalability: Design your consumers to scale horizontally to match the partition count of your event hub.

SDK Reference

For detailed API information, parameter descriptions, and examples for each language, please refer to the official SDK documentation: