Leader election in Kafka - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kafka leader election log snippet?

Given the following Kafka broker log snippet during leader election, what is the final elected leader ID?

Kafka

[2024-06-01 10:00:00] Broker 1: Starting leader election for partition 0
[2024-06-01 10:00:01] Broker 2: Received vote request from Broker 1
[2024-06-01 10:00:02] Broker 3: Voted for Broker 1
[2024-06-01 10:00:03] Broker 2: Voted for Broker 1
[2024-06-01 10:00:04] Broker 1: Leader election complete. Leader is Broker 1

A Leader is Broker 2

B Leader is Broker 1

C Leader is Broker 3

D No leader elected

💡 Hint

Look for the broker that received majority votes.

Broker 1 received votes from Broker 2 and Broker 3, which is a majority, so Broker 1 is elected leader.

🧠 Conceptual

intermediate

Which Kafka component is responsible for leader election?

In Kafka, which component manages the leader election process for partitions?

A Kafka Broker

B Kafka Producer

C Kafka Consumer

D Kafka Controller

💡 Hint

This component coordinates cluster metadata and elections.

The Kafka Controller is a special broker that manages leader election and partition assignments.

🔧 Debug

advanced

Why does this Kafka leader election fail?

Given this simplified code snippet for leader election, why does it fail to elect a leader? ```java Map votes = new HashMap<>(); votes.put(1, 1); votes.put(2, 1); if (votes.values().stream().max(Integer::compare).get() > votes.size() / 2) { System.out.println("Leader elected"); } else { System.out.println("No leader"); } ```

A The condition uses integer division causing incorrect majority check

B The votes map is empty

C The max function returns null

D The map keys are incorrect

💡 Hint

Check how division works with integers in Java.

votes.size() / 2 does integer division, so for size 2 it equals 1, making the condition incorrect for majority.

📝 Syntax

advanced

Which option correctly implements a Kafka leader election check in Python?

Select the Python code snippet that correctly checks if a candidate has majority votes in a leader election.

A

votes = {1: 2, 2: 1}
if max(votes.values()) > len(votes) // 2:
    print('Leader elected')

B

votes = {1: 2, 2: 1}
if max(votes.values()) > len(votes) / 2:
    print('Leader elected')

C

votes = {1: 2, 2: 1}
if max(votes.values()) >= len(votes) / 2:
    print('Leader elected')

D

votes = {1: 2, 2: 1}
if max(votes.values()) >= len(votes) // 2:
    print('Leader elected')

💡 Hint

Majority means strictly more than half using integer division.

Using integer division (//) ensures correct majority check. Option A uses > and // which is correct.

🚀 Application

expert

How many partitions have leaders after this Kafka cluster state update?

Given this Kafka cluster state JSON showing partition leaders, how many partitions currently have a leader assigned? ```json { "partitions": [ {"partition": 0, "leader": 1}, {"partition": 1, "leader": -1}, {"partition": 2, "leader": 2}, {"partition": 3, "leader": -1}, {"partition": 4, "leader": 3} ] } ```

A 4

B 2

C 3

D 5

💡 Hint

Leader -1 means no leader assigned.

Partitions 0, 2, and 4 have leaders (1, 2, 3). Partitions 1 and 3 have leader -1 meaning no leader.