.. _controlcenter_clients:

Client Guide
============

To use :ref:`Data Stream Monitoring <streammonitoringguide>`, you need to install the Confluent Monitoring Interceptor
with your applications, and configure your applications to use the interceptor to send metrics to Control Center.
This guide explains how to do this.

Installing the Confluent Monitoring Interceptor
-----------------------------------------------

With Kafka 0.10.0.0+, Kafka Clients support pluggable *interceptors* to examine (and potentially
modify) messages. Confluent Control Center uses an interceptor that collects statistics on incoming and outgoing
messages to provide Data Stream Monitoring.

To use Confluent Control Center's :ref:`Data Stream Monitoring <streammonitoringguide>` feature, first you need to
install the Confluent Metric Interceptor on client machines. Detailed instructions for getting Confluent Platform
clients are provided at :ref:`controlcenter_install`.

We recommend using a build tool like Maven, Ivy, or Gradle when developing Java applications. Here is some sample
content for a POM file for maven. First, you need to specify the :ref:`Confluent maven repository <installation_maven>`:

.. sourcecode:: xml

   <repositories>
     ...
     <repository>
       <id>confluent</id>
       <url>http://packages.confluent.io/maven/</url>
     </repository>
     ...
   </repositories>

Next, you can add dependencies. To monitor a producer or consumer with Control Center, you need to include the
dependencies for the Apache Kafka Java clients and the Confluent Monitoring Interceptor:

.. sourcecode:: xml

    <dependencies>
      ...
        <dependency>
            <groupId>org.apache.kafka</groupId>
            <artifactId>kafka-clients</artifactId>
            <version>0.10.0.1-cp1</version>
        </dependency>
        <dependency>
            <groupId>io.confluent</groupId>
            <artifactId>monitoring-interceptors</artifactId>
            <version>3.0.1</version>
        </dependency>
      ...
     <dependencies>

Configuring Applications to use the Confluent Monitoring Interceptor
--------------------------------------------------------------------

After you have configured your applications to include the Confluent Monitoring Interceptor, you must configure your
clients to use the interceptor.

Adding the interceptor to your Kafka Producer
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If you are not using any interceptors currently, you will need to add a new item to the Java ``Properties`` object that
you use to create a new Producer. Specifically, you need to set ``interceptor.classes`` to
``io.confluent.monitoring.clients.interceptor.MonitoringProducerInterceptor``. If you are already using an interceptor,
then you need to add an additional item to ``interceptor.classes``.

Adding the interceptor to your Kafka Consumer
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If you are not using any interceptors currently, you will need to add a new item to the Java ``Properties`` object that
you use to create a new Consumer. Specifically, you need to set ``interceptor.classes`` to
``io.confluent.monitoring.clients.interceptor.MonitoringConsumerInterceptor``. If you are already using an interceptor,
then you need to add an additional item to ``interceptor.classes``.

.. warning::

   The producer and consumer interceptor classes are different; make sure you choose the correct class for each
   producer and consumer.

Confluent Monitoring Interceptor Configuration
----------------------------------------------
We provide some configuration parameters that allow you to configure the Confluent Control Center
interceptors.

In CP 3.0, the interceptors will send and receive messages using the same Kafka cluster that you are monitoring,
and will use a set of default topics to share information. The interceptors will also report data at a regular
interval of, by default, 15 seconds.

Logging
^^^^^^^
Both the Apache Kafka client and the Confluent interceptor use ``slf4j`` for logging errors and other information.
To enable logging, you need to configure an slf4j binding, or you will see an error message like "Failed to load class
org.slf4j.impl.StaticLoggerBinder." The simplest way to resolve this issue is to add `` slf4j-simple.jar`` to your
classpath. For more details, see http://www.slf4j.org/codes.html#StaticLoggerBinder.


.. _interceptor_configuration_options:

Interceptor configuration options
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
We allow you to change the behavior of the interceptors.

You can change *any* Kafka producer configuration option for the interceptor by prefixing it with
``confluent.monitoring.interceptor.`` (including the ``.`` on the end). For example, you can change the value of
``timeout.ms`` for the interceptor using the property ``confluent.monitoring.interceptor.timeout.ms``.
For more information on Kafka producer options, see the
`Apache Kafka Producer documentation <https://kafka.apache.org/documentation.html#producerconfigs>`_.

There are also some configuration parameters that are only used by the interceptor:

``confluent.monitoring.interceptor.topic``
    Topic on which monitoring data will be written. (Default is ``_confluent.monitoring``.)
``confluent.monitoring.interceptor.publishMs``
    Period the interceptor should use to publish messages to. (Default is 15 seconds.)
``confluent.monitoring.interceptor.client.id``
     A logical client name to be included in Confluent Control Center monitoring data. If not specified, client id of an
     intercepted client with ``confluent.monitoring.interceptor`` is used.
     
Example Interceptor Configuration
----------------------------------
Below shows how to setup stream monitoring for the built-in performance testing tools that come with Kafka.  The instructions assume you have a cluster setup similar to that of the :ref:`quickstart guide<controlcenterquickstart>`.

1. With Control Center already running, open a terminal and run the following commands to start the Producer Performance Test tool with the ``MonitoringProducerInterceptor``

   .. sourcecode:: bash
   
      $ export CLASSPATH=./share/java/monitoring-interceptors/monitoring-interceptors-3.0.1.jar
      $ ./bin/kafka-producer-perf-test --topic c3test --num-records 10000000 --record-size 1000 \
      --throughput 10000 --producer-props bootstrap.servers=localhost:9092 \
      interceptor.classes=io.confluent.monitoring.clients.interceptor.MonitoringProducerInterceptor acks=all
   
2. In a separate terminal, start up the console consumer with the ``MonitoringConsumerInterceptor``

   .. sourcecode:: bash
   
      $ export CLASSPATH=./share/java/monitoring-interceptors/monitoring-interceptors-3.0.1.jar
      $ echo "interceptor.classes=io.confluent.monitoring.clients.interceptor.MonitoringConsumerInterceptor" > /tmp/consumer.config
      $ echo "group.id=c3_example_consumer_group" >> /tmp/consumer.config
      $ bin/kafka-console-consumer --topic c3test --new-consumer --bootstrap-server localhost:9092 --consumer.config /tmp/consumer.config

3. Open up the Control Center UI at `http://localhost:9021/ <http://localhost:9021/>`__ and click on ``Stream Monitoring`` to view the stream monitoring UI for the ``c3_example_consumer_group``.