Kafka Client Guide

To use Stream Monitoring, you need to install the Confluent Monitoring Interceptors with your applications, and configure your applications to use the interceptor to send metrics to Control Center. This guide explains how to do this.

Interceptor Installation

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 Stream Monitoring.

To use Confluent Control Center’s Stream Monitoring feature, first you need to install the Confluent Metric Interceptor on client machines. Detailed instructions for getting Confluent Platform clients are provided at Installation.

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 Confluent maven repository:

<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:

<dependencies>
  ...
    <dependency>
        <groupId>org.apache.kafka</groupId>
        <artifactId>kafka-clients</artifactId>
        <version>0.10.3.0-SNAPSHOT</version>
    </dependency>
    <dependency>
        <groupId>io.confluent</groupId>
        <artifactId>monitoring-interceptors</artifactId>
        <version>3.3.1-SNAPSHOT</version>
    </dependency>
  ...
 <dependencies>

Compatibility

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

Interceptor installation for 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 platform:

  • Linux (Debian and RedHat based distributions): install the confluent-librdkafka-plugins package from the Confluent repositories.
  • Mac OS X: download the monitoring interceptor zip file 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 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.

Client Configuration

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.

Note

For librdkafka-based clients, see Adding the interceptor to librdkafka-based client applications.

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.

Note

For librdkafka-based clients, see Adding the interceptor to librdkafka-based client applications.

Adding interceptors to your Kafka Streams application

For Kafka producers and consumers used internally, you can specify the Confluent Monitoring Interceptor to be used.

For producers, you need to set producer.interceptor.classes to io.confluent.monitoring.clients.interceptor.MonitoringProducerInterceptor.

For consumers, you will need to set consumer.interceptor.classes to io.confluent.monitoring.clients.interceptor.MonitoringConsumerInterceptor.

Note

Instead of hardcoding the config names in code, you can use prefixes defined in the corresponding classes like so:

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

Adding the interceptor to librdkafka-based client applications

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

C example:
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:
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.

Interceptor Configuration

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

By default, 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.

Configuration options

We allow you to change the behavior of the interceptors. (In most applications, we recommend keeping the default.)

Important

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.

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.

Security

When configuring Monitoring Interceptor for a secure cluster, the embedded producer (that sends monitoring data to the broker) in Monitoring Interceptor needs to have the correct security configurations prefixed with confluent.monitoring.interceptor.

Example Configs:

confluent.monitoring.interceptor.security.protocol=SSL
confluent.monitoring.interceptor.ssl.truststore.location=/var/private/ssl/kafka.client.truststore.jks
confluent.monitoring.interceptor.ssl.truststore.password=test1234
confluent.monitoring.interceptor.ssl.keystore.location=/var/private/ssl/kafka.client.keystore.jks
confluent.monitoring.interceptor.ssl.keystore.password=test1234
confluent.monitoring.interceptor.ssl.key.password=test1234

librdkafka-based client configuration example:

confluent.monitoring.interceptor.security.protocol=SSL
confluent.monitoring.interceptor.ssl.ca.location=/var/private/ssl/local-ca.cert
confluent.monitoring.interceptor.ssl.certificate.location=/var/private/ssl/kafka.client.pem
confluent.monitoring.interceptor.ssl.key.location=/var/private/ssl/kafka.client.key
confluent.monitoring.interceptor.ssl.key.password=test1234

While the confluent.monitoring.interceptor. prefix is the same, the actual client configuration properties depend on the underlying client and 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 Quickstart guide.

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

    $ export CLASSPATH=./share/java/monitoring-interceptors/monitoring-interceptors-3.3.1.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
    

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

    $ (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

    $ export CLASSPATH=./share/java/monitoring-interceptors/monitoring-interceptors-3.3.1.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
    

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

    $ 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 Control Center UI at 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:

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, Control Center currently will not display messages that have not been consumed.