Create an MQTT sink connector
==============================

The `MQTT sink connector <https://docs.lenses.io/5.0/integrations/connectors/stream-reactor/sinks/mqttsinkconnector/>`_ copies messages from an Apache Kafka® topic to an MQTT queue. 

.. note::

    You can check the full set of available parameters and configuration options in the `connector's documentation <https://docs.lenses.io/5.0/integrations/connectors/stream-reactor/sinks/mqttsinkconnector/>`_.

.. Tip::

    The connector can be used to sink messages to RabbitMQ® where `RabbitMQ MQTT plugin <https://www.rabbitmq.com/mqtt.html>`_ is enabled. 


.. _connect_mqtt_rbmq_sink_prereq:

Prerequisites
-------------

To set up an MQTT sink connector, you need an Aiven for Apache Kafka service :doc:`with Kafka Connect enabled <enable-connect>` or a :ref:`dedicated Aiven for Apache Kafka Connect cluster <apache_kafka_connect_dedicated_cluster>`. 

.. Tip::

   The connector will write to a topic defined in the ``"connect.mqtt.kcql"`` configuration, so either create the topic in your Kafka service, or enable the ``auto_create_topic`` parameter so that the topic will be created automatically.

Furthermore you need to collect the following information about the sink MQTT server upfront:

* ``USERNAME``: The MQTT username to connect
* ``PASSWORD``: The password for the username selected
* ``HOST``: The MQTT hostname
* ``PORT``: MQTT port (usually 1883)
* ``KCQL_STATEMENT``: The KCQL statement to be used in the following format:
  
  .. code::
     
     INSERT INTO <mqtt-topic> SELECT FIELD, ... FROM <kafka-topic>

* ``APACHE_KAFKA_HOST``: The hostname of the Apache Kafka service, only needed when using Avro as data format
* ``SCHEMA_REGISTRY_PORT``: The Apache Kafka's schema registry port, only needed when using Avro as data format
* ``SCHEMA_REGISTRY_USER``: The Apache Kafka's schema registry username, only needed when using Avro as data format
* ``SCHEMA_REGISTRY_PASSWORD``: The Apache Kafka's schema registry user password, only needed when using Avro as data format


Setup an MQTT sink connector with Aiven Console
------------------------------------------------

The following example demonstrates how to setup an Apache Kafka MQTT sink connector using the `Aiven Console <https://console.aiven.io/>`_.

Define a Kafka Connect configuration file
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Define the connector configurations in a file (we'll refer to it with the name ``mqtt_sink.json``) with the following content. Creating a file is not strictly necessary but allows to have all the information in one place before copy/pasting them in the `Aiven Console <https://console.aiven.io/>`_:

.. code::

    {
        "name": "CONNECTOR_NAME",
        "connect.mqtt.hosts": "tcp://<HOST>:<PORT>",
        "connect.mqtt.kcql": "KCQL_STATEMENT",
        "connector.class": "com.datamountaineer.streamreactor.connect.mqtt.sink.MqttSinkConnector",
        "connect.mqtt.username": "USERNAME",
        "connect.mqtt.password": "PASSWORD",
        "key.converter": "org.apache.kafka.connect.json.JsonConverter",
        "value.converter": "org.apache.kafka.connect.json.JsonConverter"
    }

The configuration file contains the following entries:

* ``name``: the connector name, replace ``CONNECTOR_NAME`` with the name you want to use for the connector.
* ``connect.mqtt.hosts``, ``connect.mqtt.kcql``, ``connect.mqtt.username`` and ``connect.mqtt.password``: sink MQTT parameters collected in the :ref:`prerequisite <connect_mqtt_rbmq_sink_prereq>` phase. 
* ``key.converter`` and ``value.converter``: The data converter used for this example JSON converter is used.
    
Check out the `dedicated documentation <https://docs.lenses.io/5.0/integrations/connectors/stream-reactor/sinks/mqttsinkconnector/#options>`_ for the full list of parameters.

Create a Kafka Connect connector with the Aiven Console
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To create a Apache Kafka Connect connector, follow these steps: 

1. Log in to the `Aiven Console <https://console.aiven.io/>`_ and select the Aiven for Apache Kafka® or Aiven for Apache Kafka Connect® service where the connector needs to be defined. 
2. Select **Connectors** from the left sidebar. 
3. Select **Create New Connector**, the button is enabled only for services :doc:`with Kafka Connect enabled <enable-connect>`.
4. Select **Stream Reactor MQTT Sink Connector**.
5. In the **Common** tab, locate the **Connector configuration** text box and select on **Edit**.
6. Paste the connector configuration (stored in the ``mqtt_sink.json`` file) in the form.
7. Select **Apply**.

   To create the connector, access the `Aiven Console <https://console.aiven.io/>`_ and select the Aiven for Apache Kafka® or Aiven for Apache Kafka® Connect service where the connector needs to be defined, then:

   .. Note::

      The Aiven Console parses the configuration file and fills the relevant UI fields. You can review the UI fields across the various tabs and change them if necessary. The changes will be reflected in JSON format in the **Connector configuration** text box.

8. After all the settings are correctly configured, select **Create connector**.
9. Verify the connector status under the **Connectors** screen.
10. Verify the presence of the data in the target Apache Kafka topic, the topic name is the one defined in the ``KCQL_STATEMENT``.

.. Tip::

   You can also create connectors using the :ref:`Aiven CLI command <avn_service_connector_create>`.