Azure Event Hubs Documentation

Using the Schema Registry with Azure Event Hubs

The Azure Event Hubs Schema Registry is a service that allows you to centrally manage and validate schemas for the events you send and receive. This ensures data consistency, facilitates schema evolution, and improves data quality across your event-driven applications.

What is Schema Registry?

Schema Registry provides a centralized repository for your event schemas. It supports various schema formats, with Avro being a popular choice for its robust schema evolution capabilities. By enforcing schemas, you can prevent unexpected data structures from polluting your event streams and ensure that consumers can reliably process incoming data.

Key Benefits

• Data Consistency: Enforces a standardized format for your events.
• Schema Evolution: Manages changes to schemas over time without breaking existing producers or consumers (when compatibility rules are followed).
• Data Validation: Validates events against registered schemas before they are sent to Event Hubs or after they are consumed.
• Centralized Management: A single source of truth for all your event schemas.

Getting Started with Schema Registry

To use Schema Registry, you first need to create a Schema Registry resource in Azure. This can be done through the Azure portal, Azure CLI, or SDKs.

Step 1: Create a Schema Registry Resource

Navigate to the Azure portal and search for "Schema Registry". Click "Create" and follow the prompts to provision a new Schema Registry instance. You'll typically associate it with an Event Hubs namespace.

Step 2: Register a Schema Group

Within your Schema Registry resource, you need to create a Schema Group. A Schema Group is a logical container for related schemas.

Step 3: Register Your First Schema

Once a Schema Group is created, you can register your event schemas. For example, let's define an Avro schema for an order event.

{
  "type": "record",
  "name": "OrderCreated",
  "namespace": "com.example.events",
  "fields": [
    { "name": "orderId", "type": "string" },
    { "name": "customerId", "type": "string" },
    { "name": "orderDate", "type": "long", "logicalType": "timestamp-millis" },
    { "name": "totalAmount", "type": "double" }
  ]
}
            

You can register this schema using the Azure portal, CLI, or SDKs. The Schema Registry will assign a unique ID to this schema version.

Integrating with Event Hubs Producers

When producing events, you'll use an Event Hubs SDK that integrates with the Schema Registry. The process typically involves:

1. Serializing your event object into the chosen schema format (e.g., Avro).
2. Encoding the serialized event with the schema ID.
3. Sending the encoded event to Event Hubs.

Example (Conceptual - Pseudocode/High-Level SDK Usage)

// Assuming you have an EventHubProducerClient and SchemaRegistryClient
var eventData = new { orderId = "123", customerId = "abc", orderDate = DateTime.UtcNow, totalAmount = 99.99 };

// Serialize and register the event with Schema Registry, getting the schema ID back
string avroSerializedEvent = SerializeAvro(eventData, schemaRegistryClient, "order-events");
int schemaId = GetSchemaId(avroSerializedEvent); // This step is often abstracted by the SDK

// Construct the EventData with schema information
var eventBody = EncodeEventWithSchemaId(avroSerializedEvent, schemaId); // e.g., Prepend schema ID bytes

await producerClient.SendAsync(new EventData(eventBody));
            

Integrating with Event Hubs Consumers

When consuming events, you'll need to:

1. Receive the event from Event Hubs.
2. Extract the schema ID from the event body.
3. Retrieve the corresponding schema from the Schema Registry using the ID.
4. Deserialize the event body using the retrieved schema.

Example (Conceptual - Pseudocode/High-Level SDK Usage)

# Assuming you have an EventProcessorClient and SchemaRegistryClient
async for event in events:
    # Extract schema ID (this format depends on encoding)
    schema_id = ExtractSchemaId(event.body)
    
    # Get the schema definition from Schema Registry
    schema_definition = schema_registry_client.get_schema(schema_id)
    
    # Deserialize the event body
    deserialized_event = DeserializeAvro(event.body, schema_definition)
    
    print(f"Received Order: {deserialized_event['orderId']}")
            

Schema Compatibility

Schema Registry supports different compatibility modes (e.g., BACKWARD, FORWARD, FULL). Understanding these modes is crucial for managing schema changes effectively. For instance, a BACKWARD-compatible schema change allows older producers to write data that newer consumers can read. Conversely, a FORWARD-compatible change allows newer producers to write data that older consumers can read.

Conclusion

Leveraging Azure Event Hubs Schema Registry is a fundamental practice for building robust, scalable, and maintainable event-driven architectures. It ensures data integrity, simplifies schema management, and enhances collaboration between development teams.