.. _controlcenter_clients:

Confluent Monitoring Interceptors
=================================

To use :ref:`Stream Monitoring <controlcenter_userguide_monitoring>` in |c3-short|, install the Confluent Monitoring
Interceptors with your Kafka applications and configure your applications to use the interceptors on
the Kafka messages produced and consumed, that are then sent to |c3-short|. This guide explains how to do this.

Installing Interceptors
-----------------------

Since Kafka 0.10.0.0, Kafka Clients support pluggable *interceptors* to examine (and potentially
modify) messages. |c3| requires clients to use Confluent Monitoring Interceptors to collect statistics on incoming and outgoing
messages to provide Stream Monitoring capabilities.

To use |c3|'s :ref:`Stream Monitoring <controlcenter_userguide_monitoring>` feature, first you must
install the Confluent Monitoring Interceptor on client machines.

Java Clients
~~~~~~~~~~~~

Maven, Ivy, or Gradle when developing Java applications. Here is sample content for a POM file for Maven. First, 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, add dependencies for the Apache Kafka Java clients and the Confluent Monitoring Interceptors:

.. codewithvars:: xml

    <dependencies>
      ...
        <dependency>
            <groupId>org.apache.kafka</groupId>
            <artifactId>kafka-clients</artifactId>
            <version>|kafka_release|</version>
        </dependency>
        <dependency>
            <groupId>io.confluent</groupId>
            <artifactId>monitoring-interceptors</artifactId>
            <version>|release|</version>
        </dependency>
      ...
     <dependencies>


librdkafka-based Clients
~~~~~~~~~~~~~~~~~~~~~~~~

For librdkafka-based clients such as confluent-kafka-python, confluent-kafka-go, or confluent-kafka-dotnet, a separate
monitoring interceptor plugin is used which is distributed differently depending on the platform:

* Linux (Debian and RedHat based distributions): install the ``confluent-librdkafka-plugins`` package from the
  :ref:`Confluent repositories <installation>`.
* macOS: download the `monitoring interceptor zip file <http://packages.confluent.io/archive/4.0/confluent-librdkafka-plugins-0.11.0.zip>`_
  and unzip the ``monitoring-interceptor.dylib`` file to the same directory as your application or a directory in the system library search path, such as ``/usr/local/lib``.
* Windows: download the `monitoring interceptor zip file <http://packages.confluent.io/archive/4.0/confluent-librdkafka-plugins-0.11.0.zip>`_
  and unzip the appropriate ``monitoring-interceptor.dll`` for your architecture to the same location as your application is installed or the directory it is run from.

.. note::
   The monitoring interceptor plugin for librdkafka-based clients requires librdkafka version 0.11.0 or later.

.. note::
   The monitoring interceptor plugin is a runtime dependency and is not required to build the client or application,
   the plugin is directly referenced through configuration properties (``plugin.library.paths``) and must be installed
   on the deployment host rather than the build host.


.. _controlcenter_client_interceptor_config:

Enabling Interceptors
---------------------

After you have installed the Confluent Monitoring Interceptor package to your Kafka applications, configure your clients to actually use the interceptors.  How you configure your clients depends on what kind of client it is.

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

Java Producers and Consumers
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can specify the Confluent Monitoring Interceptor to be used for Java producers and consumers.

For producers, set ``interceptor.classes`` to ``io.confluent.monitoring.clients.interceptor.MonitoringProducerInterceptor``.

.. sourcecode:: java

   producerProps.put(
      ProducerConfig.INTERCEPTOR_CLASSES_CONFIG,
      "io.confluent.monitoring.clients.interceptor.MonitoringProducerInterceptor");

For consumers, set ``interceptor.classes`` to ``io.confluent.monitoring.clients.interceptor.MonitoringConsumerInterceptor``.

.. sourcecode:: java

   consumerProps.put(
      ConsumerConfig.INTERCEPTOR_CLASSES_CONFIG,
      "io.confluent.monitoring.clients.interceptor.MonitoringConsumerInterceptor");

.. note::
   For librdkafka-based clients, see :ref:`section on librdkafka <add_ic_librdkafka>`.


Kafka Streams
~~~~~~~~~~~~~

Kafka Streams uses Kafka producers and consumers internally. You can specify the Confluent Monitoring Interceptor to be used for those internal producers and consumers.

For producers, set ``producer.interceptor.classes`` to ``io.confluent.monitoring.clients.interceptor.MonitoringProducerInterceptor``.
For consumers, set ``consumer.interceptor.classes`` to ``io.confluent.monitoring.clients.interceptor.MonitoringConsumerInterceptor``.

.. sourcecode:: java

   streamsConfig.put(
      StreamsConfig.PRODUCER_PREFIX + ProducerConfig.INTERCEPTOR_CLASSES_CONFIG,
      "io.confluent.monitoring.clients.interceptor.MonitoringProducerInterceptor");

   streamsConfig.put(
      StreamsConfig.CONSUMER_PREFIX + ConsumerConfig.INTERCEPTOR_CLASSES_CONFIG,
      "io.confluent.monitoring.clients.interceptor.MonitoringConsumerInterceptor");


KSQL
~~~~

KSQL, like Kafka Streams, uses Kafka producers and consumers internally. You can specify the Confluent Monitoring Interceptor to be used for those internal producers and consumers.

For producers, set ``producer.interceptor.classes`` to ``io.confluent.monitoring.clients.interceptor.MonitoringProducerInterceptor``.
For consumers, set ``consumer.interceptor.classes`` to ``io.confluent.monitoring.clients.interceptor.MonitoringConsumerInterceptor``.

.. codewithvars:: bash

   producer.interceptor.classes=io.confluent.monitoring.clients.interceptor.MonitoringProducerInterceptor
   consumer.interceptor.classes=io.confluent.monitoring.clients.interceptor.MonitoringConsumerInterceptor


.. _add_ic_librdkafka:

librdkafka-based clients
~~~~~~~~~~~~~~~~~~~~~~~~

For librdkafka-based clients, set the ``plugin.library.paths`` configuration property to the name of the interceptor library, ``monitoring-interceptor``.

C example:
  .. sourcecode:: C

     rd_kafka_conf_t *conf = rd_kafka_conf_new();
     rd_kafka_conf_res_t r;
     char errstr[512];

     r = rd_kafka_conf_set(conf, "bootstrap.servers", "mybroker", errstr, sizeof(errstr));
     if (r != RD_KAFKA_CONF_OK)
       fatal("%s", errstr);

     r = rd_kafka_conf_set(conf, "plugin.library.paths", "monitoring-interceptor", errstr, sizeof(errstr));
     if (r != RD_KAFKA_CONF_OK)
       fatal("%s", errstr);

     rd_kafka_t *rk = rd_kafka_new(RD_KAFKA_PRODUCER, conf, errstr, sizeof(errstr));
     if (!rk)
       fatal("%s", errstr);

     rd_kafka_destroy(rk);


Python example:
   .. sourcecode:: Python

      p = confluent_kafka.Producer({'bootstrap.servers': 'mybroker',
                                    'plugin.library.paths': 'monitoring-interceptor'})


.. note::
   If the monitoring-interceptor library is installed to a non-standard location which is not covered
   by the systems dynamic linker path (see ``dlopen(3)`` or ``LoadLibrary`` documentation) a full or relative
   path needs to be configured.

.. note::
   The platform-specific library filename extension (e.g., ``.so`` or ``.dll``) may be omitted.


Kafka Connect
~~~~~~~~~~~~~

Kafka Connect connectors use Kafka producers and consumers internally. You can specify the Confluent Monitoring Interceptor to be used for those internal producers and consumers.

* Source connector: configure the Confluent Monitoring Interceptors with the ``producer`` prefix.

  .. codewithvars:: bash

    producer.interceptor.classes=io.confluent.monitoring.clients.interceptor.MonitoringProducerInterceptor

* Sink connector: configure the Confluent Monitoring Interceptors with the ``consumer`` prefix.

  .. codewithvars:: bash

    consumer.interceptor.classes=io.confluent.monitoring.clients.interceptor.MonitoringConsumerInterceptor


Confluent Replicator
~~~~~~~~~~~~~~~~~~~~

Replicator uses a Kafka consumer internally. You can specify the Confluent Monitoring Interceptor to be used for that internal consumer. Modify the Replicator JSON configuration file. Here is an example subset of configuration to add.

.. codewithvars:: bash

    {
      "name":"replicator",
        "config":{
          ....
          "src.consumer.interceptor.classes": "io.confluent.monitoring.clients.interceptor.MonitoringConsumerInterceptor",
          ....
        }
      }
    }


.. _interceptor_configuration_options:


Configuring Interceptors
------------------------

Defaults
~~~~~~~~

By default, Confluent Monitoring 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.


General Options
~~~~~~~~~~~~~~~

Here are some recommended configuration parameters to use for the Confluent Monitoring Interceptors, although the defaults
can be used for many applications.

``confluent.monitoring.interceptor.bootstrap.servers``
    List of Kafka brokers in a cluster to which monitoring data will be written. (Default is ``localhost:9092``.)

.. note::

  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 Confluent Monitoring 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 |c3| monitoring data. If not specified, client id of an
     intercepted client with ``confluent.monitoring.interceptor`` is used.


Security
~~~~~~~~

When configuring Monitoring Interceptor for a secure cluster, the embedded producer (that sends monitoring data to the broker) in
Monitoring Interceptor must have the correct :ref:`security configurations <kafka_ssl_authentication>` prefixed with ``confluent.monitoring.interceptor.``

Please see more information on how to enable security for Confluent Monitoring Interceptors:

* :ref:`SSL Encryption <encryption-ssl-interceptors>`
* :ref:`SSL Authentication <authentication-ssl-interceptors>`
* :ref:`SASL/PLAIN Authentication <sasl_plain_interceptors>`
* :ref:`SASL/SCRAM Authentication <sasl_scram_interceptors>`
* :ref:`SASL/GSSAPI Authentication <sasl_gssapi_interceptors>`


For librdkafka-based clients, while the ``confluent.monitoring.interceptor.`` prefix is the same, the actual client configuration properties
may vary depending on the underlying client. They may differ between the Java client and librdkafka-based clients.


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.

The librdkafka-based monitoring interceptor will log critical errors to stderr.
To enable interceptor-specific debugging (to stderr) set the ``confluent.monitoring.interceptor.icdebug``
configuration property to ``true``.

Example 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:`quick start guide<quickstart>`.

1. With |c3-short| already running, open a terminal and run the following commands to start the Producer Performance Test tool with the ``MonitoringProducerInterceptor``

   .. codewithvars:: bash

         export CLASSPATH=./share/java/monitoring-interceptors/monitoring-interceptors-|release|.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

   For librdkafka-based clients, e.g. kafkacat:

   .. codewithvars:: bash

         (for i in $(seq 1 100000) ; echo $i ; sleep 0.01 ; done) | kafkacat -b localhost:9092 -P -t c3test -X acks=all \
        -X plugin.library.paths=monitoring-interceptor


2. In a separate terminal, start up the console consumer with the ``MonitoringConsumerInterceptor``

   .. codewithvars:: bash

         export CLASSPATH=./share/java/monitoring-interceptors/monitoring-interceptors-|release|.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 --bootstrap-server localhost:9092 --consumer.config /tmp/consumer.config

   For librdkafka-based clients, e.g. kafkacat:

   .. codewithvars:: bash

         kafkacat -b localhost:9092 -G c3_example_consumer_group -X auto.offset.reset=earliest \
        -X plugin.library.paths=monitoring-interceptor \
        c3test


3. Open up the |c3-short| 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``.

Verification
------------

To verify the interceptors are properly sending data to the ``_confluent-monitoring`` topic, start the console consumer:

.. codewithvars:: bash

  bin/control-center-console-consumer <control-center.properties> --topic --from-beginning _confluent-monitoring

You should see monitoring messages with the relevant ``clientId`` being produced onto that topic.

.. note::

  Make sure interceptor is working for both producers and consumers, |c3-short| currently will not display messages that have not been consumed.


Caveats
-------

1. Confluent Monitoring Interceptors currently **do not** support consumers with ```isolation.level=read_committed```
   and producers with ```transactional.id``` set.

2. Confluent Monitoring Interceptors will skip messages with missing or invalid timestamps, make sure all brokers and
   topics are all configured with ``log.message.format.version`` and ``message.format.version`` >= ``0.10.0``