Kafka Connect sink connector for writing data from Kafka to MQTT.

KCQL support 

The following KCQL is supported:

INTO <mqtt-topic>
FROM <kafka-topic>


-- Insert into /landoop/demo all fields from kafka_topicA
INSERT INTO /landoop/demo SELECT * FROM kafka_topicA

-- Insert into /landoop/demo all fields from dynamic field
INSERT INTO `$field` SELECT * FROM control.boxes.test WITHTARGET = field


Dynamic targets 

The connector can dynamic write to MQTT topics determined by a field in the Kafka message value using the WITHTARGET target clause and specifing $field as the target in the KCQL statement.

Kafka payload support 

This sink supports the following Kafka payloads:

  • Schema.Struct and Struct (Avro)
  • Schema.Struct and JSON
  • No Schema and JSON

See connect payloads for more information.

Error polices 

The connector supports Error polices.


Launch the stack 

  1. Copy the docker-compose file.
  2. Bring up the stack.
export CONNECTOR=mqtt
docker-compose up -d mqtt

Prepare the target system 

Login into the MongoDB container and create the container

docker exec -ti mongo mongo

create a database by inserting a dummy record:

Start the connector 

If you are using Lenses, login into Lenses and navigate to the connectors page, select MQTT as the sink and paste the following:

connect.mqtt.kcql=INSERT INTO /lenses/orders SELECT * FROM orders

To start the connector using the command line, log into the lenses-box container:

docker exec -ti lenses-box /bin/bash

and create a file containing the properties above.

Create the connector, with the connect-cli:

connect-cli create mqtt <

connect-cli create mqtt <

Wait for the connector to start and check it’s running:

connect-cli status mqtt

Inserting test data 

In the to lenses-box container start the kafka producer shell:

kafka-avro-console-producer \
 --broker-list localhost:9092 --topic orders \
 --property value.schema='{"type":"record","name":"myrecord","fields":[{"name":"id","type":"int"},{"name":"created","type":"string"},{"name":"product","type":"string"},{"name":"price","type":"double"}, {"name":"qty", "type":"int"}]}'

the console is now waiting for your input, enter the following:

  "id": 1,
  "created": "2016-05-06 13:53:00",
  "product": "OP-DAX-P-20150201-95.7",
  "price": 94.2,
  "qty": 100

Check for data in MQTT 

docker exec -ti mqtt mosquitto_sub -t /lenses/orders

Clean up 

Bring down the stack:

docker-compose down


NameDescriptionTypeDefault Value
connect.mqtt.hostsContains the MQTT connection end points.string
connect.mqtt.usernameContains the Mqtt connection user namestring
connect.mqtt.passwordContains the Mqtt connection passwordpassword
connect.mqtt.service.qualitySpecifies the Mqtt quality of serviceint
connect.mqtt.timeoutProvides the time interval to establish the mqtt connectionint3000
connect.mqtt.keep.aliveThe keep alive functionality assures that the connection is still open and both broker and client are connected to the broker during the establishment of the connection. The interval is the longest possible period of time, which broker and client can endure without sending a message.int5000
connect.mqtt.client.idContains the Mqtt session client idstring
connect.mqtt.error.policySpecifies the action to be taken if an error occurs while inserting the data. There are two available options: NOOP - the error is swallowed THROW - the error is allowed to propagate. RETRY - The exception causes the Connect framework to retry the message. The number of retries is based on The error will be logged automaticallystringTHROW
connect.mqtt.retry.intervalThe time in milliseconds between retries.int60000
connect.mqtt.max.retriesThe maximum number of times to try the write again.int20
connect.mqtt.retained.messagesSpecifies the Mqtt retained flag.booleanfalse
connect.mqtt.converter.throw.on.errorIf set to false the conversion exception will be swallowed and everything carries on BUT the message is lost!!; true will throw the exception.Default is false.booleanfalse
connect.converter.avro.schemasIf the AvroConverter is used you need to provide an avro Schema to be able to read and translate the raw bytes to an avro record. The format is $MQTT_TOPIC=$PATH_TO_AVRO_SCHEMA_FILE in case of source converter, or $KAFKA_TOPIC=PATH_TO_AVRO_SCHEMA in case of sink converterstring
connect.mqtt.kcqlContains the Kafka Connect Query Language describing the sourced MQTT source and the target Kafka topicsstring
connect.progress.enabledEnables the output for how many records have been processedbooleanfalse the path to the CA certificate file to use with the Mqtt connectionstring
connect.mqtt.ssl.certProvides the path to the certificate file to use with the Mqtt connectionstring
connect.mqtt.ssl.keyCertificate private [config] key file path.string
Last modified: July 3, 2024