Leader election in Kafka - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the leader election strategy in Kafka configuration.

Kafka

props.put("leader.election.strategy", "[1]");

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

Aorg.apache.kafka.controller.KafkaLeaderElectionStrategy

Borg.apache.kafka.controller.LeaderElectionStrategy

Corg.apache.kafka.controller.ZkLeaderElectionStrategy

Dorg.apache.kafka.controller.DefaultLeaderElectionStrategy

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a generic or non-existent class name.

Confusing Zookeeper based strategy with Kafka's internal strategy.

The correct leader election strategy class in Kafka is KafkaLeaderElectionStrategy.

2fill in blank

medium

Complete the code to configure the leader election timeout in milliseconds.

Kafka

props.put("leader.election.timeout.ms", "[1]");

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

A1000

B60000

C5000

D30000

Attempts:

3 left

💡 Hint

Common Mistakes

Setting the timeout too low causing frequent leader elections.

Using values that are too high causing slow failover.

The leader election timeout is commonly set to 30000 milliseconds (30 seconds) to allow stable leader election.

3fill in blank

hard

Fix the error in the code to correctly start leader election on the controller.

Kafka

controller.[1]LeaderElection();

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

Astart

Brun

Cbegin

Dinitiate

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'initiate' or 'begin' which are not valid method names.

Using 'run' which is unrelated here.

The correct method to start leader election on the controller is startLeaderElection().

4fill in blank

hard

Fill both blanks to create a map of partition to leader with condition on leader id.

Kafka

Map<Integer, String> leaderMap = partitions.stream()
  .filter(p -> p.leader().id() [1] 0)
  .collect(Collectors.toMap(p -> p.partition(), p -> p.[2]()));

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

A>

BgetLeader

Cleader

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' in the filter condition.

Using 'getLeader' which is not a method on partition.

The filter checks for leader id greater than 0 using '>'. The leader method returns the leader info.

5fill in blank

hard

Fill all three blanks to create a map of topic to leader id for partitions with leader id greater than 0.

Kafka

Map<String, Integer> topicLeaderMap = partitions.stream()
  .filter(p -> p.[1]().id() [2] 0)
  .collect(Collectors.toMap(p -> p.[3](), p -> p.leader().id()));

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

Aleader

B==

Ctopic

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '>' in the filter.

Using 'partition()' instead of 'topic()' for the map key.

Filter uses 'leader()' method and '>' operator to check leader id. The map key is the topic name.

Practice

1. What is the main purpose of leader election in Kafka?

easy

A. To backup data to external storage

B. To balance the load evenly among all brokers

C. To choose one broker to lead and coordinate tasks

D. To monitor client connections

Solution

1. Step 1: Understand leader election role

   Leader election picks one broker as the leader to manage partition tasks.

2. Step 2: Compare options

   Only To choose one broker to lead and coordinate tasks describes choosing a broker to lead and coordinate tasks, which matches Kafka's leader election purpose.

3. Final Answer:

   To choose one broker to lead and coordinate tasks -> Option C

4. Quick Check:

   Leader election = choose leader broker [OK]

Hint: Leader election picks one leader broker, not all brokers [OK]

Common Mistakes:

• Confusing leader election with load balancing
• Thinking leader election backs up data
• Assuming leader election monitors clients

2. Which of the following is the correct way to configure Kafka broker IDs for leader election?

easy

A. broker.id=unique_integer_per_broker

B. broker.id=localhost

C. broker.id=auto_assign

D. broker.id=0.0.0.0

Solution

1. Step 1: Identify broker ID type

   Kafka requires each broker to have a unique integer ID for leader election.

2. Step 2: Check options

   Only broker.id=unique_integer_per_broker uses a unique integer, while others use invalid or non-integer values.

3. Final Answer:

   broker.id=unique_integer_per_broker -> Option A

4. Quick Check:

   Broker ID must be unique integer [OK]

Hint: Broker ID must be a unique integer, not a string or IP [OK]

Common Mistakes:

• Using hostnames or IPs as broker IDs
• Setting broker.id to zero or non-unique values
• Assuming auto assignment works without config

3. Given the following Kafka cluster state, which broker will be the leader for partition 0?

Broker 1: ISR = [1, 2, 3]
Broker 2: ISR = [1, 2, 3]
Broker 3: ISR = [1, 2, 3]
Current leader: Broker 2
Broker 2 fails

medium

A. Broker 2

B. Broker 1

C. Broker 3

D. No leader assigned

Solution

1. Step 1: Understand ISR and leader failover

   ISR (In-Sync Replicas) are eligible leaders. When current leader fails, next ISR broker becomes leader.

2. Step 2: Identify next leader after Broker 2 fails

   Broker 1 and 3 are in ISR. Kafka picks the lowest broker ID in ISR as new leader, so Broker 1.

3. Final Answer:

   Broker 1 -> Option B

4. Quick Check:

   Next leader = lowest ISR broker after failure [OK]

Hint: Leader election picks lowest ISR broker if current leader fails [OK]

Common Mistakes:

• Choosing failed broker as leader
• Picking broker outside ISR
• Assuming no leader assigned after failure

4. You have a Kafka cluster where leader election is not working properly. Which of the following is the most likely cause?

medium

A. Each broker has a unique broker.id

B. Zookeeper is running and connected

C. Partitions have multiple replicas

D. All brokers have the same broker.id

Solution

1. Step 1: Identify leader election requirements

   Leader election requires each broker to have a unique broker.id to distinguish them.

2. Step 2: Analyze causes

   If all brokers share the same broker.id, leader election cannot assign a unique leader, causing failure.

3. Final Answer:

   All brokers have the same broker.id -> Option D

4. Quick Check:

   Unique broker IDs needed for leader election [OK]

Hint: Check broker IDs; duplicates break leader election [OK]

Common Mistakes:

• Assuming Zookeeper connection causes failure
• Thinking multiple replicas cause election failure
• Ignoring broker.id uniqueness

5. In a Kafka cluster using KRaft mode (without Zookeeper), how does leader election differ from the traditional Zookeeper-based approach?

hard

A. KRaft uses an internal quorum of controllers to elect leaders without external Zookeeper

B. KRaft requires manual leader assignment by the admin

C. KRaft disables leader election and uses round-robin partition assignment

D. KRaft uses Zookeeper but with a different election algorithm

Solution

1. Step 1: Understand KRaft mode leader election

   KRaft mode replaces Zookeeper with an internal controller quorum that manages leader election.

2. Step 2: Compare options

   Only KRaft uses an internal quorum of controllers to elect leaders without external Zookeeper correctly states KRaft uses internal quorum without external Zookeeper for leader election.

3. Final Answer:

   KRaft uses an internal quorum of controllers to elect leaders without external Zookeeper -> Option A

4. Quick Check:

   KRaft = internal quorum leader election [OK]

Hint: KRaft replaces Zookeeper with internal controller quorum [OK]

Common Mistakes:

• Thinking KRaft disables leader election
• Assuming manual leader assignment in KRaft
• Believing KRaft still uses external Zookeeper