Kafka Upstream

This plugin converts requests into Apache Kafka messages and publishes them to a specified Kafka topic.
For more details, see Kafka topics.

Kong Gateway also offers a separate Kafka Log plugin for streaming logs to Kafka topics.

This plugin uses the lua-resty-kafka client.

When encoding request bodies, several things happen:

• For requests with a content-type header of application/x-www-form-urlencoded, multipart/form-data, or application/json, this plugin passes the raw request body in the body attribute, and tries to return a parsed version of those arguments in body_args. If this parsing fails, an error message is returned and the message is not sent.
• If the content-type is not text/plain, text/html, application/xml, text/xml, or application/soap+xml, then the body will be base64-encoded to ensure that the message can be sent as JSON. In such a case, the message has an extra attribute called body_base64 set to true.

The Kafka Upstream plugin supports integration with Confluent Schema Registry for AVRO and JSON schemas.

Schema registries provide a centralized repository for managing and validating schemas for data formats like AVRO and JSON. Integrating with a schema registry allows the plugin to validate and serialize/deserialize messages in a standardized format.

Using a schema registry with Kong Gateway provides several benefits:

• Data validation: Ensures messages conform to a predefined schema before being processed.
• Schema evolution: Manages schema changes and versioning.
• Interoperability: Enables seamless communication between different services using standardized data formats.
• Reduced overhead: Minimizes the need for custom validation logic in your applications.

To learn more about Kong’s supported schema registry, see:

• Confluent Schema Registry Documentation
• AVRO Specification

How schema registry validation works

When a producer plugin is configured with a schema registry, the following workflow occurs:

 
sequenceDiagram
autonumber
    participant Client
    participant Kong as Kafka Upstream plugin
    participant Registry as Schema Registry
    participant Kafka
    
    activate Client
    activate Kong
    Client->>Kong: Send request
    deactivate Client
    activate Registry
    Kong->>Registry: Fetch schema from registry
    Registry-->>Kong: Return schema
    deactivate Registry
    Kong->>Kong: Validate message against schema
    Kong->>Kong: Serialize using schema
    activate Kafka
    Kong->>Kafka: Forward to Kafka
    deactivate Kong
    deactivate Kafka
  

If validation fails, the request is rejected with an error message.

Configure schema registry

To configure Schema Registry with the Kafka Upstream plugin, use the config.schema_registry parameter in your plugin configuration.

See the schema registry configuration example for sample configuration values.

Known limitations:

1. Message compression is not supported.
2. In Kong Gateway 3.9 or earlier, the message format is not customizable.