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

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
• ...

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.