Subscribing to topics in Kafka - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Kafka Consumer Subscription Behavior

What will be the output of this Kafka consumer code snippet when it subscribes to a topic and polls for records?

Kafka

from kafka import KafkaConsumer

consumer = KafkaConsumer(
    'my_topic',
    bootstrap_servers=['localhost:9092'],
    auto_offset_reset='earliest',
    consumer_timeout_ms=1000
)

messages = []
for message in consumer:
    messages.append(message.value.decode('utf-8'))

print(messages)

A An empty list [] because the consumer does not subscribe to any topic

B A list of all messages from the beginning of 'my_topic' if any exist, e.g., ['msg1', 'msg2']

C A runtime error because 'auto_offset_reset' is not a valid parameter

D A list containing only the latest message from 'my_topic'

💡 Hint

Check how 'auto_offset_reset' affects the starting point of message consumption.

The consumer subscribes to 'my_topic' and starts reading from the earliest offset due to 'auto_offset_reset="earliest"'. It collects all messages available during the poll and prints them as a list.

🧠 Conceptual

intermediate

Understanding Kafka Consumer Group Subscription

In Kafka, what happens when multiple consumers in the same group subscribe to the same topic?

A Messages are load balanced so each message is delivered to only one consumer in the group.

B Each consumer receives all messages from the topic independently.

C Only the first consumer receives messages; others remain idle.

D Consumers receive messages only if they subscribe to different topics.

💡 Hint

Think about how Kafka distributes partitions among consumers in a group.

Kafka divides topic partitions among consumers in the same group so each message is processed by only one consumer, enabling parallel processing without duplication.

🔧 Debug

advanced

Why does this Kafka consumer not receive messages?

Given this Kafka consumer code, why does it not receive any messages even though the topic has data?

Kafka

from kafka import KafkaConsumer

consumer = KafkaConsumer(
    bootstrap_servers=['localhost:9092'],
    group_id='group1'
)
consumer.subscribe(['my_topic'])

for message in consumer:
    print(message.value.decode('utf-8'))

A The topic name is incorrect; it should be 'my-topic' with a dash.

B The consumer forgot to call 'poll()' before iterating over messages.

C The consumer must specify 'enable_auto_commit=False' to receive messages.

D The consumer does not specify 'auto_offset_reset', so it starts at the latest offset and misses existing messages.

💡 Hint

Check the default behavior of 'auto_offset_reset' when no committed offset exists.

Without 'auto_offset_reset' set to 'earliest', the consumer starts reading from the latest offset, so it misses all existing messages in the topic.

📝 Syntax

advanced

Identify the syntax error in Kafka consumer subscription code

Which option contains a syntax error in subscribing a Kafka consumer to multiple topics?

Kafka

from kafka import KafkaConsumer

consumer = KafkaConsumer(bootstrap_servers=['localhost:9092'])
consumer.subscribe(topics=['topic1', 'topic2'])

A consumer.subscribe(['topic1', 'topic2'])

B consumer.subscribe(topic=['topic1', 'topic2'])

C consumer.subscribe('topic1', 'topic2')

D consumer.subscribe(topics=['topic1', 'topic2'])

💡 Hint

Check the method signature for 'subscribe' in KafkaConsumer.

'subscribe' expects a single argument: a list of topic names or a pattern. Passing multiple string arguments without a list causes a syntax error.

🚀 Application

expert

Determine the number of partitions assigned to each consumer

You have a Kafka topic with 6 partitions and 3 consumers in the same group subscribing to it. How many partitions will each consumer be assigned?

A Each consumer will be assigned 2 partitions.

B Each consumer will be assigned all 6 partitions.

C One consumer gets 4 partitions, others get 1 each.

D Partitions are assigned randomly, so counts vary each time.

💡 Hint

Kafka tries to balance partitions evenly among consumers in a group.

Kafka assigns partitions evenly among consumers in a group. With 6 partitions and 3 consumers, each gets 2 partitions.