kafka

Kafka Bindings

This document defines how to describe Kafka-specific information on AsyncAPI.

Version

Current version is 0.3.0.

Server Binding Object

This object contains information about the server representation in Kafka.

Fixed Fields

Field Name	Type	Description	Applicability [default]	Constraints
schemaRegistryUrl	string (url)	API URL for the Schema Registry used when producing Kafka messages (if a Schema Registry was used)	OPTIONAL	-
schemaRegistryVendor	string	The vendor of Schema Registry and Kafka serdes library that should be used (e.g. apicurio, confluent, ibm, or karapace)	OPTIONAL	MUST NOT be specified if schemaRegistryUrl is not specified
bindingVersion	string	The version of this binding.	OPTIONAL [latest]

Example

servers:
  production:
    bindings:
      kafka:
        schemaRegistryUrl: 'https://my-schema-registry.com'
        schemaRegistryVendor: 'confluent'
        bindingVersion: '0.3.0'

Channel Binding Object

This object contains information about the channel representation in Kafka (eg. a Kafka topic).

Fixed Fields

Field Name	Type	Description	Applicability [default]	Constraints
topic	string	Kafka topic name if different from channel name.	OPTIONAL	-
partitions	integer	Number of partitions configured on this topic (useful to know how many parallel consumers you may run).	OPTIONAL	Must be positive
replicas	integer	Number of replicas configured on this topic.	OPTIONAL	MUST be positive
bindingVersion	string	The version of this binding. If omitted, "latest" MUST be assumed.	OPTIONAL [latest]	-

This object MUST contain only the properties defined above.

Example

This example is valid for any Confluent compatible schema registry. Here we describe the implementation using the first 4 bytes in payload to store schema identifier.

channels:
  user-signedup:
    bindings:
      kafka:
        topic: 'my-specific-topic-name'
        partitions: 20
        replicas: 3
        bindingVersion: '0.3.0'

Operation Binding Object

This object contains information about the operation representation in Kafka (eg. the way to consume messages)

Fixed Fields

Field Name	Type	Description	Applicability [default]	Constraints
groupId	Schema Object	Id of the consumer group.	OPTIONAL	-
clientId	Schema Object	Id of the consumer inside a consumer group.	OPTIONAL	-
bindingVersion	string	The version of this binding. If omitted, "latest" MUST be assumed.	OPTIONAL [latest]	-

This object MUST contain only the properties defined above.

Example

channels:
  user-signedup:
    subscribe:
      bindings:
        kafka:
          groupId:
            type: string
            enum: ['myGroupId']
          clientId:
            type: string
            enum: ['myClientId']
          bindingVersion: '0.3.0'

Message Binding Object

This object contains information about the message representation in Kafka.

Fixed Fields

Field Name	Type	Description
key	Schema Object | AVRO Schema Object	The message key. NOTE: You can also use the reference object way.
schemaIdLocation	string	If a Schema Registry is used when performing this operation, tells where the id of schema is stored (e.g. header or payload).
schemaIdPayloadEncoding	string	Number of bytes or vendor specific values when schema id is encoded in payload (e.g confluent/ apicurio-legacy / apicurio-new).
schemaLookupStrategy	string	Freeform string for any naming strategy class to use. Clients should default to the vendor default if not supplied.
bindingVersion	string	The version of this binding. If omitted, "latest" MUST be assumed.

This object MUST contain only the properties defined above.

This example is valid for any Confluent compatible schema registry. Here we describe the implementation using the first 4 bytes in payload to store schema identifier.

channels:
  test:
    publish:
      message:
        bindings:
          kafka:
            key:
              type: string
              enum: ['myKey']
            schemaIdLocation: 'payload'
            schemaIdPayloadEncoding: '4'
            bindingVersion: '0.3.0'

This is another example that describes the use if Apicurio schema registry. We describe the apicurio-new way of serializing without details on how it's implemented. We reference a specific lookup strategy that may be used to retrieve schema Id from registry during serialization.

channels:
  test:
    publish:
      message:
        bindings:
          kafka:
            key:
              type: string
              enum: ['myKey']
            schemaIdLocation: 'payload'
            schemaIdPayloadEncoding: 'apicurio-new'
            schemaLookupStrategy: 'TopicIdStrategy'
            bindingVersion: '0.3.0'