Controller broker in Kafka - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a Kafka controller broker ID.

Kafka

controller_id = [1]

Drag options to blanks, or click blank then click option'

A-1

Bbroker_id

CNone

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 as the initial controller ID

Using None instead of an integer

Using broker_id directly without election

The controller broker ID is set to -1 initially before election.

2fill in blank

medium

Complete the code to check if the current broker is the controller.

Kafka

is_controller = (broker_id [1] controller_id)

Drag options to blanks, or click blank then click option'

A!=

B>

C<

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using != instead of ==

Using < or > which are not correct for equality check

We check if the broker ID equals the controller ID to confirm controller status.

3fill in blank

hard

Fix the error in the code to elect a new controller broker.

Kafka

new_controller = min([1])

Drag options to blanks, or click blank then click option'

Abroker_id

Bcontroller_id

Cbroker_ids

Dbrokers

Attempts:

3 left

💡 Hint

Common Mistakes

Using controller_id which is a single value

Using broker_id which is a single ID

Using brokers which may be a dict or object, not a list

The election picks the broker with the smallest ID from the list of broker IDs.

4fill in blank

hard

Fill both blanks to create a dictionary of brokers with their controller status.

Kafka

controller_status = {broker: (broker [1] controller_id) for broker in [2]

Drag options to blanks, or click blank then click option'

A==

B!=

Cbrokers

Dbroker_ids

Attempts:

3 left

💡 Hint

Common Mistakes

Using != instead of ==

Iterating over brokers object instead of broker_ids list

The dictionary comprehension maps each broker ID to True if it is the controller, else False.

5fill in blank

hard

Fill all three blanks to update the controller broker and notify all brokers.

Kafka

controller_id = [1]
for broker in [2]:
    notify(broker, [3])

Drag options to blanks, or click blank then click option'

Anew_controller

Bbroker_ids

C'controller_changed'

Dcontroller_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using controller_id instead of new_controller for assignment

Iterating over wrong variable instead of broker_ids

Sending wrong notification message

We assign the new controller ID, then notify all brokers with a 'controller_changed' message.

Practice

1.

What is the main role of the controller broker in a Kafka cluster?

easy

A. Manage leader election and cluster metadata updates

B. Store all the messages permanently

C. Serve as a client to produce messages

D. Handle consumer group offsets only

Solution

1. Step 1: Understand controller broker responsibilities

   The controller broker is responsible for managing cluster-wide tasks such as leader election and metadata updates.

2. Step 2: Compare other options

   Storing messages, producing messages, and handling consumer offsets are roles of other brokers or clients, not the controller.

3. Final Answer:

   Manage leader election and cluster metadata updates -> Option A

4. Quick Check:

   Controller broker = leader election manager [OK]

Hint: Controller broker manages cluster tasks like leader election [OK]

Common Mistakes:

• Confusing controller with brokers that store data
• Thinking controller handles only consumer offsets
• Assuming controller is a client

2.

Which of the following is the correct way to identify the controller broker using Kafka's command line tool?

kafka-metadata-quorum.sh --bootstrap-server localhost:9092 status

easy

A. Find the broker with the lowest port number

B. Check the broker with the highest broker ID

C. Look for the LeaderId in the output

D. Look for the broker with the 'leader' role in the output

Solution

1. Step 1: Understand the command output

   The kafka-metadata-quorum.sh status tool shows metadata quorum details including LeaderId, which is the ID of the current controller broker.

2. Step 2: Identify controller in output

   The controller broker is identified by the LeaderId field, not by broker ID, port number, or generic leader role.

3. Final Answer:

   Look for the LeaderId in the output -> Option C

4. Quick Check:

   LeaderId = controller broker ID [OK]

Hint: LeaderId in metadata quorum status identifies controller [OK]

Common Mistakes:

• Assuming highest broker ID means controller
• Using port number to find controller
• Confusing generic leader role with LeaderId

3.

Given the following code snippet using Kafka AdminClient in Java, what will controllerId hold after execution?

AdminClient admin = AdminClient.create(props);
Node controller = admin.describeCluster().controller().get();
int controllerId = controller.id();
admin.close();

medium

A. The total number of brokers in the cluster

B. The topic partition count

C. The port number of the controller broker

D. The broker ID of the current controller broker

Solution

1. Step 1: Analyze AdminClient describeCluster method

   The describeCluster().controller() returns the current controller broker as a Node object.

2. Step 2: Understand Node.id()

   The id() method returns the broker ID of that Node, which is the controller broker's ID.

3. Final Answer:

   The broker ID of the current controller broker -> Option D

4. Quick Check:

   controller().id() = controller broker ID [OK]

Hint: controller().id() returns controller broker's ID [OK]

Common Mistakes:

• Confusing controller ID with number of brokers
• Thinking it returns port or partition count
• Ignoring the blocking get() call

4.

Consider this snippet to get the controller broker ID using Kafka AdminClient in Java:

AdminClient admin = AdminClient.create(props);
Node controller = admin.describeCluster().controller().get();
int controllerId = controller.id();
admin.close();

What is the likely cause if this code throws a java.util.concurrent.ExecutionException?

medium

A. The close() method was called too early

B. The AdminClient failed to connect to any broker

C. The id() method returns a string, not int

D. The controller() method does not exist

Solution

1. Step 1: Understand ExecutionException cause

   An ExecutionException usually wraps an error during the async call, often connection failure.

2. Step 2: Check AdminClient connectivity

   If AdminClient cannot connect to any broker, the get() call on controller() future will fail with this exception.

3. Final Answer:

   The AdminClient failed to connect to any broker -> Option B

4. Quick Check:

   ExecutionException = connection failure [OK]

Hint: ExecutionException often means connection problem [OK]

Common Mistakes:

• Thinking method does not exist causes ExecutionException
• Confusing return types of id() method
• Assuming close() causes this error

5.

You want to write a Kafka monitoring tool that automatically detects when the controller broker changes and logs the new controller's broker ID. Which approach is best?

1. Use AdminClient to poll describeCluster().controller() periodically.
2. Subscribe to Kafka internal topics to listen for controller changes.
3. Manually check broker logs for controller election messages.
4. Restart all brokers to force controller re-election and detect changes.

hard

A. Use AdminClient to poll describeCluster().controller() periodically

B. Subscribe to Kafka internal topics to listen for controller changes

C. Manually check broker logs for controller election messages

D. Restart all brokers to force controller re-election and detect changes

Solution

1. Step 1: Evaluate monitoring approaches

   Polling describeCluster().controller() via AdminClient is a reliable, programmatic way to detect controller changes.

2. Step 2: Assess other options

   Subscribing to internal topics is complex and not guaranteed; checking logs is manual and slow; restarting brokers is disruptive and impractical.

3. Final Answer:

   Use AdminClient to poll describeCluster().controller() periodically -> Option A

4. Quick Check:

   Polling controller() is best for monitoring [OK]

Hint: Poll controller() with AdminClient for changes [OK]

Common Mistakes:

• Trying to read internal topics for controller changes
• Relying on manual log inspection
• Restarting brokers unnecessarily