kafka

Kafka Bindings

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

Version

Current version is 0.5.0.

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: '0.5.0'

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
topicConfiguration	TopicConfiguration Object	Topic configuration properties that are relevant for the API.	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:
    bindings:
      kafka:
        topic: 'my-specific-topic-name'
        partitions: 20
        replicas: 3
        topicConfiguration:
          cleanup.policy: ["delete", "compact"]
          retention.ms: 604800000
          retention.bytes: 1000000000
          delete.retention.ms: 86400000
          max.message.bytes: 1048588
        bindingVersion: '0.5.0'

TopicConfiguration Object

This objects contains information about the API relevant topic configuration in Kafka.

Field Name	Type	Description	Applicability [default]	Constraints
cleanup.policy	array	The cleanup.policy configuration option.	OPTIONAL	array may only contain delete and/or compact
retention.ms	long	The retention.ms configuration option.	OPTIONAL	see kafka documentation
retention.bytes	long	The retention.bytes configuration option.	OPTIONAL	see kafka documentation
delete.retention.ms	long	The delete.retention.ms configuration option.	OPTIONAL	see kafka documentation
max.message.bytes	integer	The max.message.bytes configuration option.	OPTIONAL	see kafka documentation
confluent.key.schema.validation	boolean	It shows whether the schema validation for the message key is enabled. Vendor specific config.	OPTIONAL	-
confluent.key.subject.name.strategy	string	The name of the schema lookup strategy for the message key. Vendor specific config.	OPTIONAL	Clients should default to the vendor default if not supplied.
confluent.value.schema.validation	boolean	It shows whether the schema validation for the message value is enabled. Vendor specific config.	OPTIONAL	-
confluent.value.subject.name.strategy	string	The name of the schema lookup strategy for the message value. Vendor specific config.	OPTIONAL	Clients should default to the vendor default if not supplied.

This object MAY contain the properties defined above including optional additional properties.

Example

topicConfiguration:
  cleanup.policy: ["delete", "compact"]
  retention.ms: 604800000
  retention.bytes: 1000000000
  delete.retention.ms: 86400000
  max.message.bytes: 1048588
  confluent.key.schema.validation: true
  confluent.key.subject.name.strategy: "TopicNameStrategy"
  confluent.value.schema.validation: true
  confluent.value.subject.name.strategy: "TopicNameStrategy"

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 | Reference Object	Id of the consumer group.	OPTIONAL	-
clientId	Schema Object | Reference 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:
operations:
  userSignup:
    action: receive
    bindings:
      kafka:
        groupId:
          type: string
          enum: ['myGroupId']
        clientId:
          type: string
          enum: ['myClientId']
        bindingVersion: '0.5.0'

Message Binding Object

This object contains information about the message representation in Kafka.

Fixed Fields

Field Name	Type	Description	Applicability [default]	Constraints
key	Schema Object | Reference Object | AVRO Schema Object	The message key. NOTE: You can also use the reference object way.	OPTIONAL	-
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).	OPTIONAL	MUST NOT be specified if schemaRegistryUrl is not specified at the Server level
schemaIdPayloadEncoding	string	Number of bytes or vendor specific values when schema id is encoded in payload (e.g confluent/ apicurio-legacy / apicurio-new).	OPTIONAL	MUST NOT be specified if schemaRegistryUrl is not specified at the Server level
schemaLookupStrategy	string	Freeform string for any naming strategy class to use. Clients should default to the vendor default if not supplied.	OPTIONAL	MUST NOT be specified if schemaRegistryUrl is not specified at the Server level
bindingVersion	string	The version of this binding. If omitted, "latest" MUST be assumed.	OPTIONAL [latest]	-

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:
    address: test-topic
    messages:
      testMessage:
        bindings:
          kafka:
            key:
              type: string
              enum: ['myKey']
            schemaIdLocation: 'payload'
            schemaIdPayloadEncoding: '4'
            bindingVersion: '0.5.0'

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:
    address: test-topic
    messages:
      testMessage:
        bindings:
          kafka:
            key:
              type: string
              enum: ['myKey']
            schemaIdLocation: 'payload'
            schemaIdPayloadEncoding: 'apicurio-new'
            schemaLookupStrategy: 'TopicIdStrategy'
            bindingVersion: '0.5.0'