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MQTT Broker and Proxy

The MQTT Broker and Proxy is an embedded lightweight MQTT Broker that can also store messages from specified MQTT topics to Kafka topics.

  • All configuration properties follow the standard Kafka configuration system and can be specified in the server properties file.
  • Authentication is optional; if username and password are not set, clients can connect without credentials.
  • The MQTT Broker is lightweight broker compliant with MQTT 5 and MQTT 3

Configuration

Enable/Disable Configuration

lc.mqtt.broker.enable

  • Type: Boolean
  • Default: false
  • Description: Controls whether the embedded MQTT broker is enabled. When set to false, the MQTT proxy will not start.

MQTT Broker Settings

mqtt.host

  • Type: String
  • Default: 0.0.0.0
  • Description: The host address the embedded MQTT broker will bind to. The default value 0.0.0.0 means the broker will listen on all available network interfaces.

mqtt.port

  • Type: Integer
  • Default: 1883
  • Range: 1 to 65535
  • Description: The port number for the embedded MQTT broker.

Authentication Settings

mqtt.auth.username

  • Type: String
  • Default: null (no authentication required)
  • Description: A shared username that all MQTT clients must use to connect. If not specified, authentication is disabled.

mqtt.auth.password

  • Type: Password
  • Default: null (no authentication required)
  • Description: A shared password that all MQTT clients must use to connect. If not specified, authentication is disabled.

Kafka Connection Settings

mqtt.kafka.bootstrap.servers

  • Type: String
  • Default: Uses the Kafka server's advertised brokers
  • Description: A comma-separated list of host:port pairs to establish the initial connection to the Kafka cluster. If not specified, the proxy will use the Kafka server's advertised brokers.

mqtt.kafka.client.id

  • Type: String
  • Default: mqtt-kafka-proxy
  • Description: An identifier for the Kafka producer client.

Topic Mapping Configuration

mqtt.topic.mapping.<mqtt-topic-filter>=<kafka-topic>

  • Format: Configuration properties with prefix mqtt.topic.mapping.
  • Description: Defines how MQTT topics are mapped to Kafka topics. The portion after the prefix is the MQTT topic filter, and the value is the target Kafka topic name.
  • Wildcard Support: The single-level wildcard + is supported in MQTT topic filters to match any value at a single topic level.
  • Example: mqtt.topic.mapping.devices/+/temperature=kafka-temperature-topic maps any MQTT topic matching the pattern devices/+/temperature (e.g., devices/sensor1/temperature, devices/sensor2/temperature) to the Kafka topic kafka-temperature-topic.

The + wildcard matches exactly one topic level and can be used at any position in the topic filter.