MQTT

A Kafka Connect source connector to read events from MQTT and push them to Kafka.

KCQL support 

The following KCQL is supported:

INSERT INTO <your-kafka-topic>
SELECT *
FROM <your-mqtt-topic>
[WITHCONVERTER=`myclass`]

Selection of fields from the JMS message is not supported.

Examples:

-- Insert mode, select all fields from topicA
-- and write to topic topic with converter myclass
INSERT INTO topic SELECT * FROM /mqttTopicA [WITHCONVERTER=myclass]

-- wildcard
INSERT INTO topic SELECT * FROM /mqttTopicA/+/sensors [WITHCONVERTER=`myclass`]

Concepts 

Keyed JSON format 

In order to facilitate scenarios like retaining the latest value for a given device identifier, or support Kafka Streams joins without having to re-map the topic data the connector supports WITHKEY in the KCQL syntax.

Multiple keys fields are supported using a delimiter:

// `[` enclosed by `]` denotes optional values
WITHKEY(field1 [, field2.A , field3]) [KEYDELIMITER='.']

The resulting Kafka record key content will be the string concatenation for the values of the fields specified. Optionally the delimiter can be set via the KEYDELIMITER keyword.

Shared and Wildcard Subscriptions 

The connector supports both wildcard and shared subscriptions but the KCQL command must be placed inside single quotes.

-- wildcard
INSERT INTO kafkaTopic1
SELECT * FROM /mqttTopicA/+/sensors
WITHCONVERTER=`myclass`

Message converters 

The connector supports converters to handle different messages payload format in the source topic. See source record converters.

Quickstart 

Launch the stack 

1. Copy the docker-compose file.
2. Bring up the stack.

export CONNECTOR=mqtt
docker-compose up -d mqtt

Inserting test data 

Login into the mqtt container:

docker exec \
    -ti mqtt \
    mosquitto_pub \
    -m "{\"deviceId\":1,\"value\":31.1,\"region\":\"EMEA\",\"timestamp\":1482236627236}" \
    -d -r -t /mjson

Start the connector 

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

name=mqtt-source
connector.class=com.datamountaineer.streamreactor.connect.mqtt.source.MqttSourceConnector
tasks.max=1
connect.mqtt.kcql=INSERT INTO mqtt SELECT * FROM /mjson WITHCONVERTER=`com.datamountaineer.streamreactor.connect.converters.source.JsonSimpleConverter`
connect.mqtt.client.id=dm_source_id
connect.mqtt.hosts=tcp://mqtt:1883
connect.mqtt.service.quality=1

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

docker exec -ti lenses-box /bin/sh

and create a connector.properties file containing the properties above.

Create the connector, with the connect-cli:

connect-cli create mqtt < connector.properties

connect-cli create mqtt < connector.properties

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

connect-cli status mqtt

Check for records in Kafka 

Check the records in Lenses or with via the console:

kafka-avro-console-consumer \
    --bootstrap-server localhost:9092 \
    --topic mqtt \
    --from-beginning

Clean up 

Bring down the stack:

docker-compose down

Options