JMX metrics in Kafka - Commands & Configuration

Introduction

JMX metrics help you watch how your Kafka server is doing by showing numbers about its health and activity. This helps you find problems early and keep your system running smoothly.

When you want to see how many messages your Kafka broker is processing per second.

When you need to check if your Kafka server is running out of memory or CPU.

When you want to monitor the number of active connections to your Kafka broker.

When you want to track the lag of consumers to ensure they are keeping up with producers.

When you want to collect metrics to send to a monitoring system like Prometheus or Grafana.

Config File - kafka-server-start.sh

kafka-server-start.sh

#!/bin/bash

KAFKA_HEAP_OPTS="-Xmx1G -Xms1G"
JMX_PORT=9999
export KAFKA_HEAP_OPTS
export JMX_PORT

exec /usr/bin/kafka-server-start /etc/kafka/server.properties

This script sets the Java heap size for Kafka and enables JMX on port 9999. The JMX_PORT environment variable tells Kafka to open that port for JMX monitoring. The last line starts the Kafka server with its configuration file.

Commands

This command lists all Java processes running on the machine to confirm Kafka is running.

Terminal

jps

Expected Output

12345 Kafka

67890 Jps

This command opens the JMX console connected to Kafka's JMX port to view live metrics in a graphical interface.

Terminal

jconsole localhost:9999

Expected Output

No output (command runs silently)

If Kafka is configured with a JMX exporter, this command fetches metrics in text format for monitoring tools.

Terminal

curl http://localhost:9999/metrics

Expected Output

kafka_server_broker_topic_metrics_messages_in_total 123456

kafka_server_broker_topic_metrics_bytes_in_total 78901234

Key Concept

If you remember nothing else from JMX metrics, remember: JMX lets you watch Kafka's health and activity numbers live to catch problems early.

Common Mistakes

Not setting the JMX_PORT environment variable before starting Kafka.

Kafka won't open the JMX port, so no metrics will be available for monitoring.

Always export JMX_PORT with a valid port number before starting Kafka.

Trying to connect to JMX on the wrong port or host.

The connection will fail because Kafka listens on the port set by JMX_PORT on the correct host.

Verify the JMX_PORT value and connect to the correct host and port.

Expecting metrics output from curl without configuring a JMX exporter.

Kafka does not expose HTTP metrics by default; curl will fail or return nothing.

Install and configure a JMX exporter like Prometheus JMX exporter to expose metrics over HTTP.

Summary

Set the JMX_PORT environment variable before starting Kafka to enable JMX metrics.

Use jconsole or similar tools to connect to Kafka's JMX port and view metrics live.

Configure a JMX exporter to expose metrics over HTTP for automated monitoring.

Practice

1. What is the primary purpose of JMX metrics in Kafka?

easy

A. To configure Kafka brokers dynamically

B. To send messages between Kafka topics

C. To monitor Kafka's internal performance and health

D. To store data permanently in Kafka

Solution

1. Step 1: Understand JMX metrics role

   JMX metrics provide data about Kafka's internal state and performance.

2. Step 2: Identify the correct purpose

   Monitoring performance and health is the main use of JMX metrics in Kafka.

3. Final Answer:

   To monitor Kafka's internal performance and health -> Option C

4. Quick Check:

   JMX metrics = Monitoring Kafka [OK]

Hint: JMX metrics are for monitoring, not messaging or storage [OK]

Common Mistakes:

• Confusing metrics with message sending
• Thinking JMX configures Kafka brokers
• Assuming JMX stores Kafka data

2. Which of the following is the correct way to identify a Kafka JMX metric?

easy

A. Using a topic name and partition number

B. Using a unique ObjectName and attribute

C. Using a consumer group ID

D. Using a broker ID and port number

Solution

1. Step 1: Recall JMX metric identification

   Each JMX metric is accessed by a unique ObjectName and attribute in Kafka.

2. Step 2: Compare options

   Only Using a unique ObjectName and attribute correctly describes the identification method for JMX metrics.

3. Final Answer:

   Using a unique ObjectName and attribute -> Option B

4. Quick Check:

   JMX metric ID = ObjectName + attribute [OK]

Hint: JMX metrics use ObjectName and attribute, not topic or group IDs [OK]

Common Mistakes:

• Mixing JMX metric IDs with Kafka topic or consumer IDs
• Confusing broker info with metric identifiers
• Assuming partition number identifies metrics

3. Given the following Java snippet to get a Kafka JMX metric attribute, what will be the output if the metric value is 150?

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

medium

A. MBeanServerException

B. null

C. Count

D. 150

Solution

1. Step 1: Understand the code's purpose

   The code queries the JMX MBeanServer for the 'Count' attribute of the specified metric.

2. Step 2: Interpret the output

   If the metric value is 150, the printed output will be the integer 150.

3. Final Answer:

   150 -> Option D

4. Quick Check:

   Metric value printed = 150 [OK]

Hint: JMX attribute value prints directly if metric exists [OK]

Common Mistakes:

• Expecting attribute name instead of value
• Assuming null if metric exists
• Confusing exceptions with normal output

4. You try to read a Kafka JMX metric but get a javax.management.InstanceNotFoundException. What is the most likely cause?

medium

A. The ObjectName used does not match any registered MBean

B. The Kafka broker is down

C. The attribute name is misspelled

D. The MBeanServer is not initialized

Solution

1. Step 1: Understand the exception meaning

   InstanceNotFoundException means the requested MBean ObjectName is not found in the MBeanServer.

2. Step 2: Identify the cause

   If the ObjectName does not match any registered MBean, this exception occurs.

3. Final Answer:

   The ObjectName used does not match any registered MBean -> Option A

4. Quick Check:

   InstanceNotFoundException = Wrong ObjectName [OK]

Hint: Check ObjectName spelling if InstanceNotFoundException occurs [OK]

Common Mistakes:

• Blaming attribute name for InstanceNotFoundException
• Assuming broker down causes this exception
• Thinking MBeanServer is uninitialized

5. You want to monitor Kafka's message throughput using JMX metrics and alert if MessagesInPerSec.Count exceeds 1000. Which approach correctly combines JMX metric reading and alert logic in Java?

hard

A. Query the MBeanServer for the metric attribute, then compare the value to 1000 and trigger alert if greater

B. Subscribe to Kafka topic and count messages manually, ignoring JMX metrics

C. Use Kafka consumer lag metrics instead of MessagesInPerSec

D. Restart Kafka broker when MessagesInPerSec.Count exceeds 1000

Solution

1. Step 1: Understand monitoring with JMX

   To monitor throughput, read the MessagesInPerSec.Count attribute from Kafka's JMX MBeanServer.

2. Step 2: Implement alert logic

   Compare the retrieved metric value to 1000 and trigger an alert if it exceeds this threshold.

3. Final Answer:

   Query the MBeanServer for the metric attribute, then compare the value to 1000 and trigger alert if greater -> Option A

4. Quick Check:

   Read metric + compare + alert = Correct approach [OK]

Hint: Read metric value then compare to threshold for alert [OK]

Common Mistakes:

• Ignoring JMX metrics and counting messages manually
• Using unrelated metrics like consumer lag
• Restarting broker instead of alerting