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   this work for additional information regarding copyright ownership.
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   (the "License"); you may not use this file except in compliance with
   the License.  You may obtain a copy of the License at

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   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
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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:: property

   kyuubi.backend.server.event.loggers=CUSTOM

- Restart all the kyuubi server instances.
