Default replication factor for internal offsets topic prevents users from reading from clusters that have less than three nodes.

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
28/100
Issue type
Bug
Clarity
Needs clarification
Activity status
Stale
Tech stack
kafka, kubernetes, rust
Domain
devops, distributed-systems

Research direction

Start by tracing how the operator handles offsets.topic.replication.factor and broker-count validation when deploying Kafka clusters with fewer than three nodes. Compare the documented behavior with the proposed documentation, validation, or automatic-configuration options, then define and verify one accepted outcome for reading from small clusters.

Written by the indexing model from the issue text.

Description

type/bug

When deploying Kafka clusters with less than three nodes the default value of 3 for offsets.topic.replication.factor prohibits users from reading any values from topics.

Writing works fine, if topics are created with few enough partitions - or auto-created which observes available broker count for the replication factor.
But when reading for the first time, Kafka internally tries to create the __consumer_offsets topic, and this is required to have three partitions by default. And until this has been created no read requests are allowed.

The broker simply keeps logging

kafka [2023-05-05 15:20:39,078] INFO [Admin Manager on Broker 1001]: Error processing create topic request CreatableTopic(name='__consumer_offsets', numPartitions=50, replicationFactor=3, assignments=[], configs=[CreateableTopicConfig(name='compression.type', value='producer'), CreateableTopicConfig(name='cleanup.policy', value='compact'), CreateableTopicConfig(name='segment.bytes'
kafka org.apache.kafka.common.errors.InvalidReplicationFactorException: Replication factor: 3 larger than available brokers: 1.

Possible solutions are:

  • documentation - this is not strictly speaking a bug, but also not nice
  • catch it during validation in the operator and log an error
  • automatically set this in the config when deploying less than 3 brokers
  • ...
Dominant language
Rust
Stars
28
Forks
8
Avg merge
2d 12h
Merged PRs (30d)
9

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