Consumer group concept in Kafka - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the consumer group ID in Kafka consumer configuration.

Kafka

props.put("group.id", [1]);

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

A"my-group"

B"partition-0"

C"topic-name"

D"localhost"

Attempts:

3 left

💡 Hint

Common Mistakes

Using the topic name instead of the group ID.

Using server address instead of group ID.

The group.id property sets the consumer group identifier, which is essential for Kafka to manage consumer groups.

2fill in blank

medium

Complete the code to subscribe the consumer to a topic named "orders".

Kafka

consumer.subscribe(Collections.[1]("orders"));

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

AasList

BlistOf

CsingletonList

DemptyList

Attempts:

3 left

💡 Hint

Common Mistakes

Using emptyList which subscribes to no topics.

Using listOf which is not a Java Collections method.

The singletonList method creates an immutable list with a single element, which is used to subscribe to one topic.

3fill in blank

hard

Fix the error in the code to poll messages from Kafka consumer with a timeout of 100 milliseconds.

Kafka

ConsumerRecords<String, String> records = consumer.poll(Duration.[1](100));

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

AofMillis

BofMinutes

CofSeconds

DofNanos

Attempts:

3 left

💡 Hint

Common Mistakes

Using ofSeconds which would mean 100 seconds.

Using ofMinutes which is too long.

The poll method requires a Duration object specifying the timeout. ofMillis creates a duration in milliseconds.

4fill in blank

hard

Fill both blanks to create a map of topic partitions to offsets for committing offsets manually.

Kafka

Map<TopicPartition, OffsetAndMetadata> offsets = Map.of(new TopicPartition("orders", [1]), new OffsetAndMetadata([2]));

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

A0

B15

C10

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using an offset smaller than the last consumed offset.

Using a partition number that does not exist.

The first blank is the partition number (0), and the second blank is the offset to commit (15).

5fill in blank

hard

Fill all three blanks to create a consumer configuration with bootstrap servers, group ID, and auto offset reset policy.

Kafka

props.put("bootstrap.servers", [1]);
props.put("group.id", [2]);
props.put("auto.offset.reset", [3]);

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

A"localhost:9092"

B"my-group"

C"earliest"

D"latest"

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up bootstrap servers and group ID values.

Using an invalid auto offset reset value.

The bootstrap servers specify the Kafka cluster address, the group ID identifies the consumer group, and the auto offset reset policy defines where to start if no offset is found.

Practice

1. What is the main purpose of a consumer group in Kafka?

easy

A. To allow multiple consumers to share the work of reading messages

B. To store messages permanently in Kafka

C. To produce messages to Kafka topics

D. To encrypt messages during transmission

Solution

1. Step 1: Understand consumer group role

   A consumer group lets multiple consumers work together to read messages from a topic.

2. Step 2: Compare other options

   Storing messages, producing messages, and encrypting are not roles of consumer groups.

3. Final Answer:

   To allow multiple consumers to share the work of reading messages -> Option A

4. Quick Check:

   Consumer group = share reading work [OK]

Hint: Consumer groups split message reading among consumers [OK]

Common Mistakes:

• Confusing consumer groups with producers
• Thinking consumer groups store messages
• Assuming consumer groups encrypt data

2. Which of the following is the correct way to specify a consumer group ID in Kafka consumer configuration?

easy

A. "groupName" : "my-group"

B. "group.id" : "my-group"

C. "consumer.group" : "my-group"

D. "consumerId" : "my-group"

Solution

1. Step 1: Recall Kafka consumer config keys

   The correct key to set the consumer group is "group.id".

2. Step 2: Check other options

   Other keys like "consumer.group", "groupName", or "consumerId" are incorrect or do not exist.

3. Final Answer:

   "group.id" : "my-group" -> Option B

4. Quick Check:

   Consumer group ID key = "group.id" [OK]

Hint: Remember Kafka uses "group.id" for consumer groups [OK]

Common Mistakes:

• Using incorrect config keys
• Confusing consumer ID with group ID
• Misspelling the key name

3. Given a Kafka topic with 4 partitions and a consumer group with 2 consumers, how many partitions will each consumer read from?

medium

A. Each consumer reads from 2 partitions

B. Each consumer reads from 4 partitions

C. Each consumer reads from 1 partition

D. Each consumer reads from 0 partitions

Solution

1. Step 1: Understand partition assignment

   Partitions are divided among consumers in a group. With 4 partitions and 2 consumers, partitions split evenly.

2. Step 2: Calculate partitions per consumer

   4 partitions / 2 consumers = 2 partitions per consumer.

3. Final Answer:

   Each consumer reads from 2 partitions -> Option A

4. Quick Check:

   Partitions per consumer = total partitions / consumers = 2 [OK]

Hint: Partitions divide evenly among consumers in a group [OK]

Common Mistakes:

• Assuming each consumer reads all partitions
• Thinking partitions are not shared
• Ignoring partition count

4. What is wrong with this Kafka consumer group code snippet?

props.put("group.id", "my-group");
props.put("enable.auto.commit", "false");
consumer.subscribe(Arrays.asList("my-topic"));
consumer.poll(Duration.ofMillis(100));
// Missing commit after poll

medium

A. The poll timeout is too long

B. The group.id is incorrectly set

C. The consumer subscribes to the wrong topic

D. The consumer never commits offsets, risking message reprocessing

Solution

1. Step 1: Analyze auto commit setting

   Auto commit is disabled, so offsets must be committed manually.

2. Step 2: Check code for commit call

   Code calls poll but does not commit offsets, so messages may be reprocessed on restart.

3. Final Answer:

   The consumer never commits offsets, risking message reprocessing -> Option D

4. Quick Check:

   Auto commit false needs manual commit [OK]

Hint: Disable auto commit means manual commit needed [OK]

Common Mistakes:

• Forgetting to commit offsets manually
• Assuming auto commit is enabled by default
• Ignoring poll timeout relevance

5. You have a Kafka topic with 3 partitions and a consumer group with 4 consumers. What happens to the extra consumer?

hard

A. The extra consumer causes an error in the group

B. The extra consumer reads from all partitions

C. The extra consumer remains idle and does not receive messages

D. Kafka creates a new partition for the extra consumer

Solution

1. Step 1: Understand partition to consumer assignment

   Each partition can be assigned to only one consumer in the group.

2. Step 2: Analyze consumer count vs partitions

   With 3 partitions and 4 consumers, only 3 consumers get partitions; the 4th consumer stays idle.

3. Final Answer:

   The extra consumer remains idle and does not receive messages -> Option C

4. Quick Check:

   More consumers than partitions means idle consumers [OK]

Hint: Consumers > partitions means some consumers idle [OK]

Common Mistakes:

• Thinking Kafka creates new partitions automatically
• Assuming extra consumers share partitions
• Believing extra consumers cause errors