Confluent Monitoring Interceptors

To monitor production and consumption in Control Center, install Confluent Monitoring Interceptors with your Apache Kafka® applications, and configure your applications to use the interceptors on the Kafka messages produced and consumed. These messages are then sent to Control Center.

Installing Interceptors

Since Kafka, Kafka Clients support pluggable interceptors to examine (and potentially modify) messages. Control Center requires clients to use Confluent Monitoring Interceptors to collect statistics on incoming and outgoing messages to provide production and consumption monitoring capabilities.

To use Control Center’s production and consumption monitoring features, 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 Confluent Maven repository:


Next, add dependencies for the Kafka Java clients and the Confluent Monitoring Interceptors:


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 that is distributed differently depending on the platform:

  • Linux (Debian and RedHat based distributions): install the confluent-librdkafka-plugins package from the Confluent repositories.
  • macOS or Windows: Download the monitoring interceptor zip file, then:
    • For macOS: extract 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.
    • For Windows: extract the appropriate monitoring-interceptor.dll for your architecture to the same location as where your application is installed or the directory where your application is run.


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


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.

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 a client depends on what kind of client it is.


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


If you are using interceptors, and you are installing Confluent Platform on RHEL, CentOS, Debian or Ubuntu, you must install the component package (for example, confluent-ksql) and Confluent Control Center (confluent-control-center) on the same machine.

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.


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



For librdkafka-based clients, see 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.




ksqlDB, 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.


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:
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);

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


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.


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 these internal producers and consumers.

  • Source connector: In the worker, add the Confluent Monitoring Interceptors and use the producer prefix.

  • Sink connector: In the worker, add the Confluent Monitoring Interceptors and use the consumer prefix.



To override the monitoring interceptor bootstrap servers for metrics producers and consumers, specify the producer.<*> or consumer.<*> prefixes and any required security configuration properties, as shown in Encryption and Authentication with SSL and Encryption with SSL. For example, for a metrics producer, you could override the bootstrap servers and provide the security protocol by entering the following properties: producer.confluent.monitoring.interceptor.bootstrap.servers and

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.

      "src.consumer.interceptor.classes": "io.confluent.monitoring.clients.interceptor.MonitoringConsumerInterceptor",


To override the monitoring interceptor bootstrap servers for Replicator, specify the prefix for Replicator as the consumer in the configuration. For example: "src.consumer.confluent.monitoring.interceptor.bootstrap.servers": "kafka1:9091"

To learn more, see Interceptors for Kafka Connect and Interceptors for Replicator in Confluent Monitoring Interceptors, Confluent Monitoring Interceptor in Encryption with SSL, Monitoring Replicator, and Use Control Center to monitor replicators in the Replicator quick start tutorial.

Confluent REST Proxy

REST Proxy uses Kafka consumers and producers internally. You can instrument these with the Confluent Monitoring Interceptors for these internal clients by modifying the startup configuration properties file (/etc/kafka-rest/ You also need to include the interceptor JAR (located under share/java/monitoring-interceptors) on the CLASSPATH. Here is an example subset of the configuration to add.


REST Proxy Interceptor class configurations

REST Proxy supports interceptor configurations as part of Java new producer and consumer settings.


Producer interceptor classes.

  • Type: string
  • Default: “”
  • Importance: low

Consumer interceptor classes.

  • Type: string
  • Default: “”
  • Importance: low

Configuring Interceptors


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 15 seconds by default.

General Options

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

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


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 for the interceptor using the property For more information on Kafka producer options, see the Producer Configurations.

There are also some configuration parameters that are only used by the Confluent Monitoring Interceptor:

Topic on which monitoring data will be written. (Default is _confluent-monitoring.)
Period the interceptor should use to publish messages to. (Default is 15 seconds.)
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.


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 security configurations prefixed with confluent.monitoring.interceptor.

For more information on how to enable security for Confluent Monitoring 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.

Set up interceptors for RBAC

To use interceptors when RBAC is enabled, the producers and consumers require principal write access to the monitoring topic (default is _confluent-monitoring) on the cluster where the monitoring data is being sent. By default, the monitoring cluster is the same as the cluster being produced to and consumed from.

Follow these steps:

  1. Create the _confluent-monitoring topic by either starting Control Center or manually creating the topic.

  2. Grant the client principal the DeveloperWrite role on the _confluent-monitoring topic using the Confluent CLI.

    confluent iam rolebinding create \
    --principal User:<client-principal> \
    --role DeveloperWrite \
    --resource Topic:_confluent-monitoring
    --kafka-cluster-id <kafka-id>
  3. Start up the client.

For more infomration on RBAC in Confluent Platform, see Authorization using Role-Based Access Control and Configure RBAC for Control Center.


Both the 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

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 quick start 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-6.0.0.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-6.0.0.jar
    echo "interceptor.classes=io.confluent.monitoring.clients.interceptor.MonitoringConsumerInterceptor" > /tmp/consumer.config
    echo "" >> /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:

    kafkacat -b localhost:9092 -G c3_example_consumer_group -X auto.offset.reset=earliest \
    -X plugin.library.paths=monitoring-interceptor \
  3. Open the Control Center UI at http://localhost:9021/ and click on Consumers to view the c3_example_consumer_group. Click the consumer group ID to view its details.


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

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

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


Make sure interceptor is working for both producers and consumers; Control Center currently will not display messages that have not been consumed.


  • Confluent Monitoring Interceptors currently do not support consumers with isolation.level=read_committed and producers with set.
  • 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
  • Confluent Monitoring Interceptors cannot be configured in Confluent Control Center in conjunction with Exactly Once Semantics (EOS).