[Bug]: Clients receive MetadataResponse with 0 brokers and >0 topics during rolling upgrade, causing clients to stop reconnecting

[ida1kd]

Bug Description

Summary
During a Strimzi-managed rolling upgrade, clients intermittently receive a MetadataResponse that reports broker_cnt = 0 while topic_cnt > 0. librdkafka consumers (v2.13.0, metadata.recovery.strategy=rebootstrap) can stop rebootstrap attempts after this and remain offline until process restart.

Environment

• Strimzi: 0.45.1 / 0.49.1
• Kafka: 3.8.0 -> 3.9.1 (rolling upgrade)
• Clients: librdkafka v2.13.0

Reproduction (high level)

1. 3-broker cluster managed by Strimzi.
2. Rolling upgrade from Kafka 3.8.0 to 3.9.1.
3. During broker pod recreation (IP change, ~20–30s window), clients may receive broker_cnt=0 && topic_cnt>0.

Observed

• Client log: 0 brokers, 1 topics
• librdkafka treats this as successful metadata, decommissions brokers and stops rebootstrap timer → clients stay offline until restart.
• Full client report: librdkafka v2.13.0 Stops Rebootstrap and Clears Brokers on "0 brokers but topic>0" MetadataResponse, Causing Permanent Client Disconnection confluentinc/librdkafka#5301

Expected

• Rolling upgrade should not leave clients permanently disconnected; clients should recover once brokers are Ready.
• If Strimzi causes a transient state that yields empty broker metadata, please confirm that behavior and recommend mitigations.

Requested action

• Can maintainers confirm whether Strimzi may expose a window where broker metadata is empty during rolling upgrades?
• If this is expected, what mitigations/configuration are recommended to avoid client disconnects?

Reference

• librdkafka issue: librdkafka v2.13.0 Stops Rebootstrap and Clears Brokers on "0 brokers but topic>0" MetadataResponse, Causing Permanent Client Disconnection confluentinc/librdkafka#5301

Steps to reproduce

No response

Expected behavior

No response

Strimzi version

0.45.1

Kubernetes version

1.34

Installation method

helm chart

Infrastructure

No response

Configuration files and logs

No response

Additional context

No response

[ppatierno]

Strimzi doesn't do anything special when rolling about metadata. I think if whatever you are facing is Kafka related so you should engage with the Kafka community directly.