Azure Event Hubs

Schema Registry Concepts

The Azure Event Hubs Schema Registry is a fully managed service that allows you to store and manage schemas for your event data. It integrates seamlessly with Event Hubs, enabling robust data governance and ensuring schema compatibility across your event-driven applications.

Why Use a Schema Registry?

In a distributed, event-driven architecture, different producers and consumers interact with event streams. Without a centralized schema management system, several challenges can arise:

• Schema Evolution: As applications evolve, schemas for event data need to change. Managing these changes without breaking existing consumers can be complex.
• Data Consistency: Ensuring that all producers generate data conforming to a specific schema and that consumers can correctly interpret it is crucial for data integrity.
• Discoverability: Finding and understanding the schemas used by various event streams can be difficult in large systems.
• Interoperability: Different services might use different serialization formats. A schema registry helps standardize these formats.

Key Concepts

Schema Groups

A schema group is a logical collection of schemas that share a common purpose or represent related data. For example, you might have a schema group for 'Customer Orders' or 'IoT Device Readings'. Within a schema group, schemas are versioned.

Schemas

A schema defines the structure and data types of your event payload. Event Hubs Schema Registry supports popular schema formats, including:

• Avro (Recommended for its rich features and widespread adoption)
• JSON Schema
• Protobuf (Protocol Buffers)

Each schema in a group is associated with a version number, allowing for controlled evolution of your data structure.

Schema Versions

When you update a schema within a schema group, a new version is created. This allows producers and consumers to operate on different versions of a schema during a transition period, preventing downtime.

Serialization and Deserialization

The Schema Registry doesn't enforce a specific serialization format for the data itself, but it does define the schema. You typically use formats like Avro, JSON, or Protocol Buffers to serialize your event payload according to the registered schema. The Schema Registry then provides the schema definition needed by consumers to deserialize the data correctly.

Compatibility Rules

The Schema Registry allows you to define compatibility rules for schema evolution. Common rules include:

• Backward Compatibility: New schemas can read data written with older schemas.
• Forward Compatibility: Older schemas can read data written with new schemas.
• Full Compatibility: Both backward and forward compatibility.
• None: No compatibility enforced.

By enforcing these rules, you ensure that schema changes don't break your existing event pipelines.

Integration with Event Hubs

When you send events to Event Hubs, you can optionally include a reference to the schema used. Consumers can then query the Schema Registry using this reference to retrieve the schema and deserialize the event payload. This approach decouples the schema definition from the event data itself, making your system more flexible and manageable.

Example Scenario

Imagine an e-commerce platform:

1. A Product Service produces 'ProductUpdated' events. Initially, the schema includes 'productId', 'name', and 'price'.
2. Later, the platform adds 'description' and 'weight' to the product information. The Product Service registers a new version of the 'ProductUpdated' schema with these new fields.
3. A Catalog Service (a consumer) might still be running on the older schema. It can still process new events (backward compatibility).
4. A new Search Service might be developed to work with the latest schema, capable of reading both old and new event formats (full compatibility).

The Schema Registry manages these versions and ensures compatibility, allowing both services to coexist and evolve independently.

For more detailed information, please refer to the Schema Registry API documentation.