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   this work for additional information regarding copyright ownership.
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   distributed under the License is distributed on an "AS IS" BASIS,
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Configure Kyuubi to use Custom EventHandler
===========================================

Kyuubi provide event processing mechanism, it can help us to record some events. Beside the builtin ``JsonLoggingEventHandler``,
Kyuubi supports custom event handler. It is usually used to write Kyuubi events to some external systems.
For example, Kafka, ElasticSearch, etc. The ``org.apache.kyuubi.events.handler.CustomEventHandlerProvider`` has a zero-arg constructor,
it can help us to create a custom EventHandler.

.. code-block:: scala

   package org.apache.kyuubi.events.handler

   import org.apache.kyuubi.config.KyuubiConf
   import org.apache.kyuubi.events.KyuubiEvent

   /**
    * Custom EventHandler provider. We can implement it to provide a custom EventHandler.
    * The implementation will be loaded by ``Service Provider Interface``.
    */
   trait CustomEventHandlerProvider {

     /**
      * The create method is called to create a custom event handler
      * when this implementation is loaded.
      *
      * @param kyuubiConf The conf can be used to read some configs.
      * @return A custom handler to handle KyuubiEvent.
      */
      def create(kyuubiConf: KyuubiConf): EventHandler[KyuubiEvent]
   }

Build A Custom EventHandler
----------------------------

To create custom EventHandlerProvider class derived from the above interface, we need to:

- Referencing the library

.. parsed-literal::

   <dependency>
      <groupId>org.apache.kyuubi</groupId>
      <artifactId>kyuubi-events_2.12</artifactId>
      <version>\ |release|\</version>
      <scope>provided</scope>
   </dependency>

- Implement ``org.apache.kyuubi.events.handler.CustomEventHandlerProvider``
- Adding a file named ``org.apache.kyuubi.events.handler.CustomEventHandlerProvider`` in the src/main/resources/META-INF/services folder of project, its content is the custom class name.

Enable Custom EventHandler
----------------------------

To enable the custom EventHandler, we need to

- Put the jar package to ``$KYUUBI_HOME/jars`` directory to make it visible for
    the classpath of the kyuubi server.
- Configure the following properties to ``$KYUUBI_HOME/conf/kyuubi-defaults.conf``
  on each node where kyuubi server is installed. If you need use other event handler, it can be appended after the ``CUSTOM``.

.. code-block:: properties

   kyuubi.backend.server.event.loggers=CUSTOM

- Restart all the kyuubi server instances.
