JMX metrics in Kafka - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this JMX query for Kafka broker metrics?

Given the following JMX query executed against a Kafka broker's MBean server, what is the output?

Kafka

ObjectName name = new ObjectName("kafka.server:type=BrokerTopicMetrics,name=MessagesInPerSec");
MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
AttributeList attributes = mbs.getAttributes(name, new String[]{"Count"});
for (Attribute attr : attributes.asList()) {
    System.out.println(attr.getName() + ": " + attr.getValue());
}

A javax.management.InstanceNotFoundException

B Count: 1000

C Count: null

D Count: 0

💡 Hint

Think about the default state of the metric if no messages have been processed yet.

The 'MessagesInPerSec' metric's 'Count' attribute starts at 0 before any messages are processed. The code queries this attribute and prints its value.

❓ Predict Output

intermediate

What error does this JMX code produce when querying a non-existent Kafka metric?

Consider this Java code snippet querying a Kafka JMX metric that does not exist. What error will it produce?

Kafka

ObjectName name = new ObjectName("kafka.server:type=BrokerTopicMetrics,name=NonExistentMetric");
MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
mbs.getAttribute(name, "Count");

A javax.management.InstanceNotFoundException

B javax.management.AttributeNotFoundException

C NullPointerException

D No error, returns 0

💡 Hint

The MBean server throws an exception if the MBean name is not registered.

If the MBean with the given ObjectName does not exist, the MBeanServer throws InstanceNotFoundException.

🔧 Debug

advanced

Why does this JMX Kafka metric query return null instead of the expected value?

This Java code queries the 'BytesInPerSec' metric from Kafka but prints 'null'. What is the likely cause?

Kafka

ObjectName name = new ObjectName("kafka.server:type=BrokerTopicMetrics,name=BytesInPerSec");
MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
Object value = mbs.getAttribute(name, "OneMinuteRate");
System.out.println(value);

A The MBeanServer is not connected to the Kafka broker process

B The 'OneMinuteRate' attribute is not exposed by the MBean

C The ObjectName is incorrect and does not match any MBean

D The 'OneMinuteRate' attribute exists but its value is zero, printed as null

💡 Hint

Check the attributes exposed by the 'BytesInPerSec' MBean carefully.

The 'BytesInPerSec' MBean exposes attributes like 'Count' and 'MeanRate', but not 'OneMinuteRate'. Querying a non-existent attribute returns null.

🧠 Conceptual

advanced

Which JMX metric best indicates the current number of active Kafka connections?

Among Kafka JMX metrics, which one best reflects the current active network connections to the broker?

A kafka.network:type=SocketServer,name=ConnectionCount

B kafka.network:type=SocketServer,name=NetworkProcessorAvgIdlePercent

C kafka.server:type=BrokerTopicMetrics,name=MessagesInPerSec

D kafka.controller:type=KafkaController,name=ActiveControllerCount

💡 Hint

Look for a metric that counts connections, not rates or percentages.

The 'ConnectionCount' metric under 'kafka.network:type=SocketServer' shows the current number of active connections.

❓ Predict Output

expert

What is the output of this JMX query code snippet for Kafka's UnderReplicatedPartitions metric?

Analyze the following Java code querying Kafka's 'UnderReplicatedPartitions' metric. What will it print?

Kafka

ObjectName name = new ObjectName("kafka.server:type=ReplicaManager,name=UnderReplicatedPartitions");
MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
Integer count = (Integer) mbs.getAttribute(name, "Value");
System.out.println("UnderReplicatedPartitions: " + count);

A javax.management.AttributeNotFoundException

B UnderReplicatedPartitions: 0

C javax.management.InstanceNotFoundException

D UnderReplicatedPartitions: null

💡 Hint

Check if the ObjectName and attribute name are correct for this metric.

The 'UnderReplicatedPartitions' metric is under 'kafka.server:type=ReplicaManager,name=UnderReplicatedPartitions' but the attribute 'Value' does not exist; also, this MBean is not always registered, causing InstanceNotFoundException.