Difference between group id, Client id and id in KafkaListener Spring Boot

Question

I am starting to work with Spring Boot 2 and Spring Kafka, I don't quite understand what's the difference between group id, Client id, and id in in KafkaListener interface.
I know group ID is used by Kafka broker to manage multiple Consumer in the same group, but what about the others? what advantage do I get by setting them? where can I see the effect of setting or not setting them?

Based on their java doc :

/**
     * The unique identifier of the container managing for this endpoint.
     * <p>If none is specified an auto-generated one is provided.
     * @return the {@code id} for the container managing for this endpoint.
     * @see org.springframework.kafka.config.KafkaListenerEndpointRegistry#getListenerContainer(String)
     */
String id() default "";

/**
 * Override the {@code group.id} property for the consumer factory with this value
 * for this listener only.
 * @return the group id.
 * @since 1.3
 */
String groupId() default "";

/**
 * When provided, overrides the client id property in the consumer factory
 * configuration. A suffix ('-n') is added for each container instance to ensure
 * uniqueness when concurrency is used.
 * @return the client id prefix.
 * @since 2.1.1
 */
String clientIdPrefix() default "";

Answer 1

Your groupId understanding is correct.

The id is like a bean name in Spring Framework. However this one is used in the KafkaListenerEndpointRegistry boundaries only. So, if you need a lifecycle control over the particular KafkaListenerContainer created for the mentioned @KafkaListener, you need to inject KafkaListenerEndpointRegistry and use the mentioned getListenerContainer() for the appropriate id.

The clientIdPrefix is reflection of exact client.id property of the Kafka Consumer:

An id string to pass to the server when making requests. The purpose of this is to be able to track the source of requests beyond just ip/port by allowing a logical application name to be included in server-side request logging.