In Kafka, whether multiple consumers can read the same message from a partition depends on how the consumers are organized into consumer groups. Here's how it works:

1. Consumer Groups

• Each consumer group acts as an independent subscriber to a Kafka topic.
• Within a consumer group, each partition of the topic is assigned to only one consumer. This ensures that a single message is processed by only one consumer in the group.

Example:

• Topic: my-topic with 3 partitions.
• Consumer Group: group-A with 3 consumers (C1, C2, C3).
  • Partition 0 → Consumer C1
  • Partition 1 → Consumer C2
  • Partition 2 → Consumer C3

In this setup, no two consumers in group-A will read the same message.

2. Multiple Consumer Groups

• If you have multiple consumer groups, each group gets its own copy of the messages.
• This means the same message can be read by one consumer in each group.

Example:

• Topic: my-topic with 3 partitions.
• Consumer Groups: group-A and group-B.
  • group-A will process the messages independently.
  • group-B will also process the messages independently.

Here, messages in my-topic are delivered once to a consumer in group-A and once to a consumer in group-B.

3. Key Scenarios

4. Partition Ownership

• Kafka assigns each partition to only one consumer within a group.
• When a consumer in the group fails, the partitions assigned to it are redistributed among the remaining consumers in the group.

5. How to Enable Multiple Consumers Reading the Same Message

To allow multiple consumers to read the same message:

1. Use different consumer groups.
   • Each consumer group will independently read all messages.
2. Use topic mirroring or copy the topic data if you need additional flexibility.

Summary

• No, multiple consumers in the same group cannot read the same message.
• Yes, multiple consumers in different groups can read the same message. This behavior allows for independent processing of messages by different systems.