Send messages to Apache Kafka via targets.

Content-type

When Kafka messages are sent in Ditto Protocol, the payload should be UTF-8 encoded strings.

If messages which are not in Ditto Protocol should be processed, a payload mapping must be configured for the connection in order to transform the messages.

Specific connection configuration

The common configuration for connections in Connections > Targets applies here as well. Following are some specifics for Apache Kafka 2.x connections:

Source format

Target format

A Kafka 2.x connection requires the protocol configuration target object to have an address property. This property may have different formats:

  • topic: Contains a Kafka topic - a partition will be assigned in a round-robin fashion.
  • topic/key: Contains a Kafka topic and a key - Kafka ensures that messages with the same key end up in the same partition.
  • topic#partitionNumber: Contains a Kafka topic and a specific partition number - that partition will be used when sending records.

The target address may contain placeholders; see placeholders section for more information.

Further, "topics" is a list of strings, each list entry representing a subscription of Ditto protocol topics, see target topics and filtering for more information on that.

Outbound messages are published to the configured target address if one of the subjects in "authorizationContext" have READ permission on the Thing that is associated with a message.

{
  "address": "<kafka_topic>/<kafka_key>",
  "topics": [
    "_/_/things/twin/events",
    "_/_/things/live/messages"
  ],
  "authorizationContext": ["ditto:outbound-auth-subject"]
}

Specific configuration properties

The specific configuration properties contain the following keys:

  • bootstrapServers (required): contains a comma separated list of Kafka bootstrap servers to use for connecting to (in addition to the still required connection uri)
  • saslMechanism (required if connection uri contains username\/password): contains one of the following SASL mechanisms to use for authentication at Kafka:
    • plain
    • scram-sha-256
    • scram-sha-512

Establishing connecting to an Apache Kafka endpoint

Ditto’s Connectivity service is responsible for creating new and managing existing connections.

This can be done dynamically at runtime without the need to restart any microservice using a Ditto DevOps command.

Example connection configuration to create a new Kafka 2.x connection in order to connect to a running Apache Kafka server:

{
  "connection": {
    "id": "kafka-example-connection-123",
    "connectionType": "kafka",
    "connectionStatus": "open",
    "failoverEnabled": true,
    "uri": "tcp://user:password@localhost:9092",
    "specificConfig": {
      "bootstrapServers": "localhost:9092,other.host:9092"
      "saslMechanism": "plain"
    },
    "sources": [],
    "targets": [
      {
        "address": "topic/key",
        "topics": [
          "_/_/things/twin/events",
          "_/_/things/live/messages"
        ],
        "authorizationContext": ["ditto:outbound-auth-subject", "..."]
      }
    ]
  }
}