KAFKA-20410: Add DLQ configuration parameters for Share Groups (KIP-1191)

[sjhajharia]

Summary

This PR adds the configuration foundation for Share Groups Dead-Letter
Queue (DLQ) functionality as specified in KIP-1191: Dead-letter queues
for share
groups.

Changes

New Configurations

Cluster-level configs (ShareGroupConfig.java):

1. errors.deadletterqueue.auto.create.topics.enable (default: false)
   • Enables automatic creation of DLQ topics
2. errors.deadletterqueue.topic.name.prefix (default: "dlq.")
   • Required prefix for DLQ topic names when auto-create is enabled

Group-level configs (ShareGroupConfig.java):

1. errors.deadletterqueue.topic.name (default: "")
   • Specifies the DLQ topic name for a share group
   • Empty string means DLQ disabled for that group
2. errors.deadletterqueue.copy.record.enable (default: false)
   • When true: Copy full original record to DLQ
   • When false: Copy only context metadata (offset, delivery count,
     reason)

Topic-level config (TopicConfig.java):

1. errors.deadletterqueue.group.enable (default: not set)
   • Marks a topic as eligible for use as a DLQ

Validation Logic

• DLQ topic names must not start with __ (reserved for internal
  topics)
• When errors.deadletterqueue.auto.create.topics.enable=true, the
  topic name must start with the configured prefix
• When auto-create is disabled, topic name can be any valid Kafka topic
  name (no prefix requirement)
• Blank topic name ("") is valid and indicates DLQ is disabled

Tests

Added 7 comprehensive test cases in ShareGroupConfigTest:

• testDLQConfigDefaults() - Verify default values
• testDLQConfigCustomValues() - Validate custom configurations
• testDLQTopicNameCannotStartWithDoubleUnderscore() - Reject __
  prefix
• testDLQTopicNameMustMatchPrefixWhenAutoCreateEnabled() - Enforce
  prefix with auto-create
• testDLQTopicNamePrefixNotRequiredWhenAutoCreateDisabled() - Allow
  any name without auto-create
• testDLQBlankTopicNameIsValid() - Accept blank as "DLQ disabled"
• testDLQValidTopicNameWithAutoCreate() - Validate correct
  configuration

Reviewers: David Jacot david.jacot@gmail.com

[dajac]

All configs starts with the same prefix. Why don’t we follow the same pattern for those?

[sjhajharia]

We are intentionally not including the group.share. prefix on these configs to keep them generic enough so that in the future, we can re-use them as and when needed and maintain compatibility still.