MQTT

This page describes the usage of the Stream Reactor MQTT Source Connector.

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

Connector Class

io.lenses.streamreactor.connect.mqtt.source.MqttSourceConnector

Example

For more examples, see the tutorials.

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

KCQL support

You can specify multiple KCQL statements separated by ;

However, you can not route the same source to different topics, for this use a separate connector instance.

The following KCQL is supported:

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

The 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`]

Keyed JSON format

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 key 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 of the values of the fields. Optionally, the delimiter can be set via the KEYDELIMITER keyword.

Shared and Wildcard Subscriptions

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

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

Dynamic target topics

When using wildcard subscriptions, you can dynamically route messages to a Kafka topic with the same name as the MQTT topic by using `$`in the KCQL target statement.

You must use a wildcard or a shared subscription format.

Kafka does not support / . The result topic names will have/replaced by _. For example:

/mqttSourceTopic/A/test would become mqttSourceTopic_A_test.

INSERT INTO `$` SELECT * FROM /mqttTopicA/+/sensors

Message converters

The connector supports converters to handle different message payload formats in the source topic. See source record converters.

Option Reference

Name	Description	Type	Default Value
connect.mqtt.hosts	Contains the MQTT connection end points.	string
connect.mqtt.username	Contains the Mqtt connection user name	string
connect.mqtt.password	Contains the Mqtt connection password	password
connect.mqtt.service.quality	Specifies the Mqtt quality of service	int
connect.mqtt.timeout	Provides the time interval to establish the mqtt connection	int	3000
connect.mqtt.clean	connect.mqtt.clean	boolean	true
connect.mqtt.keep.alive	The 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.	int	5000
connect.mqtt.client.id	Contains the Mqtt session client id	string
connect.mqtt.error.policy	Specifies 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 automatically	string	THROW
connect.mqtt.retry.interval	The time in milliseconds between retries.	int	60000
connect.mqtt.max.retries	The maximum number of times to try the write again.	int	20
connect.mqtt.retained.messages	Specifies the Mqtt retained flag.	boolean	false
connect.mqtt.converter.throw.on.error	If 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.	boolean	false
connect.converter.avro.schemas	If 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 converter	string
connect.mqtt.log.message	Logs received MQTT messages	boolean	false
connect.mqtt.kcql	Contains the Kafka Connect Query Language describing the sourced MQTT source and the target Kafka topics	string
connect.mqtt.polling.timeout	Provides the timeout to poll incoming messages	int	1000
connect.mqtt.share.replicate	Replicate the shared subscriptions to all tasks instead of distributing them	boolean	false
connect.progress.enabled	Enables the output for how many records have been processed	boolean	false
connect.mqtt.ssl.ca.cert	Provides the path to the CA certificate file to use with the Mqtt connection	string
connect.mqtt.ssl.cert	Provides the path to the certificate file to use with the Mqtt connection	string
connect.mqtt.ssl.key	Certificate private [config] key file path.	string
connect.mqtt.process.duplicates	Process duplicate messages	boolean	false