Schema Registry
KSN Schema Registry provides an interface for storing and managing schemas. Producers and consumers can register the schemas within the registry and retrieve them when necessary. Schemas are versioned, and the registry supports configurable compatibility modes between different schema versions. When a producer or consumer attempts to register a new schema version, the registry performs a compatibility check and returns an error if an incompatible change is detected. This mechanism ensures consistency and compatibility among all producers and consumers when schema changes occur.
Configurable compatibility modes
When using serialization and deserialization formats such as Avro, JSON Schema, and Protobuf, we need to remember that there are different configurable compatibility modes. In the Schema Registry, schema compatibility is managed by versioning each individual schema. The compatibility type determines how the Schema Registry compares the new schema with previous versions of a schema, for a given subject. Upon its initial creation within a subject, a schema is assigned a unique identifier and a version number, starting at version 1. If the schema is updated and successfully passes the compatibility checks, it is given a new unique identifier and an incremented version number, i.e., version 2.
| Compatibility modes | AVRO | JSON | Protobuf |
| NONE | YES | YES | YES |
| BACKWARD | YES | YES | YES |
| BACKWARD_TRANSITIVE | YES | YES | YES |
| FORWARD | YES | YES | - |
| FORWARD_TRANSITIVE | YES | YES | - |
| FULL | YES | YES | - |
| FULL_TRANSITIVE | YES | YES | - |
REST API
KSN schema registry provides REST API for managing schemas. The following table lists the supported methods and parameters, more details about the API, please refer to Schema Registry API.
| API | Method | Support Parameters |
|---|---|---|
| /schemas/ids/{int: id} | GET | |
| /schemas/ids/{int: id}/schema | GET | |
| /schemas/types | GET | |
| /schemas/ids/{int: id}/versions | GET | |
| /schemas/ids/{int: id}/subjects | GET | |
| /subjects | GET | deleted (boolean), deletedOnly (boolean) |
| /subjects/(string: subject) | POST | normalize (boolean), deleted (boolean) |
| /subjects/(string: subject) | DELETE | permanent (boolean) |
| /subjects/(string: subject)/versions | POST | normalize (boolean) |
| /subjects/(string: subject)/versions | GET | deleted (boolean), deletedOnly (boolean) |
| /subjects/(string: subject)/versions/(versionId: version) | GET | deleted (boolean) |
| /subjects/(string: subject)/versions/(versionId: version) | DELETE | permanent (boolean) |
| /subjects/(string: subject)/versions/(versionId: version)/schema | GET | |
| /subjects/(string: subject)/versions/(versionId: version)/referencedby | GET | |
| /compatibility/subjects/(string: subject)/versions/latest | GET | |
| /config/(string: subject) | PUT | only support set compatibility |
| /config/(string: subject) | GET | only support get compatibility |
| /mode | GET | only support the mode READWRITE |
Use Schema Registry on Console
On the left navigation pane of StreamNative Console, in the Admin section, click Kafka Clients, and choose the Java client, then enable the Kafka Schema Registry by following switch.
Please make sure you granted permission(produce) for topic
public/__kafka_schemaregistry/__schema-registryin the following page.
We need to mention that Now the Kafka Schemas can’t work with Pulsar schemas. This is the mission of the unified schema registry.