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new a975f44cfd Add warning about KAFKA-20254 migration bug to 4.2 docs
(#824)
a975f44cfd is described below
commit a975f44cfd59edc239b12c558ef3841a9d115494
Author: Lucas Brutschy <[email protected]>
AuthorDate: Mon Mar 9 14:20:05 2026 +0100
Add warning about KAFKA-20254 migration bug to 4.2 docs (#824)
A critical broker-side bug in the offline migration code (KAFKA-20254)
affects migrations from classic to streams groups in 4.2.0. This adds warnings
to the upgrade notes, streams upgrade guide, and streams rebalance protocol
documentation advising users to wait for a later release before migrating.
---
content/en/42/getting-started/upgrade.md | 2 +-
content/en/42/streams/developer-guide/streams-rebalance-protocol.md | 2 ++
content/en/42/streams/upgrade-guide.md | 2 ++
3 files changed, 5 insertions(+), 1 deletion(-)
diff --git a/content/en/42/getting-started/upgrade.md
b/content/en/42/getting-started/upgrade.md
index 6b40e8cb70..83ab8e0a31 100644
--- a/content/en/42/getting-started/upgrade.md
+++ b/content/en/42/getting-started/upgrade.md
@@ -34,7 +34,7 @@ type: docs
* The `--max-partition-memory-bytes` option in `kafka-console-producer` is
deprecated and will be removed in Kafka 5.0. Please use `--batch-size` instead.
* Queues for Kafka ([KIP-932](https://cwiki.apache.org/confluence/x/4hA0Dw))
is production-ready in Apache Kafka 4.2. This feature introduces a new kind of
group called share groups, as an alternative to consumer groups. Consumers in a
share group cooperatively consume records from topics, without assigning each
partition to just one consumer. Share groups also introduce per-record
acknowledgement and counting of delivery attempts. Use share groups in cases
where records are processed [...]
- * The Streams Rebalance Protocol
([KIP-1071](https://cwiki.apache.org/confluence/display/KAFKA/KIP-1071%3A+Streams+Rebalance+Protocol))
is now production-ready for its core feature set. This broker-driven
rebalancing system designed specifically for Kafka Streams applications
provides faster, more stable rebalances and better observability. For more
information about the supported feature set, usage, and migration, please refer
to the [Streams developer guide](/{version}/streams/develo [...]
+ * The Streams Rebalance Protocol
([KIP-1071](https://cwiki.apache.org/confluence/display/KAFKA/KIP-1071%3A+Streams+Rebalance+Protocol))
is now production-ready for its core feature set. This broker-driven
rebalancing system designed specifically for Kafka Streams applications
provides faster, more stable rebalances and better observability. For more
information about the supported feature set, usage, and migration, please refer
to the [Streams developer guide](/{version}/streams/develo [...]
* The `org.apache.kafka.common.header.internals.RecordHeader` class has been
updated to be read thread-safe. See
[KIP-1205](https://cwiki.apache.org/confluence/x/nYmhFg) for details. In other
words, each individual `Header` object within a `ConsumerRecord`'s `headers`
can now be safely read from multiple threads concurrently.
* The `org.apache.kafka.disallowed.login.modules` config was deprecated.
Please use the `org.apache.kafka.allowed.login.modules` instead.
* The `remote.log.manager.thread.pool.size` config was deprecated. Please
use the `remote.log.manager.follower.thread.pool.size` instead.
diff --git
a/content/en/42/streams/developer-guide/streams-rebalance-protocol.md
b/content/en/42/streams/developer-guide/streams-rebalance-protocol.md
index 0b56d41134..33800ebc17 100644
--- a/content/en/42/streams/developer-guide/streams-rebalance-protocol.md
+++ b/content/en/42/streams/developer-guide/streams-rebalance-protocol.md
@@ -253,3 +253,5 @@ The only broker-side group data that will be preserved are
the committed offsets
Similarly, you can convert a streams group back to a classic group by
following the same process but setting `group.protocol=classic`.
**Warning:** Online migration (migrating while the application is running) is
not available in this version. Plan for a maintenance window when migrating
between protocols.
+
+**Warning:** Due to a critical broker-side bug in the offline migration code
([KAFKA-20254](https://issues.apache.org/jira/browse/KAFKA-20254)), we
recommend against doing migrations from classic to streams groups in 4.2.0.
Newly created streams groups are not impacted. Users planning to migrate should
upgrade their brokers to a later release that includes the fix.
diff --git a/content/en/42/streams/upgrade-guide.md
b/content/en/42/streams/upgrade-guide.md
index bec8f25d34..a201d2a108 100644
--- a/content/en/42/streams/upgrade-guide.md
+++ b/content/en/42/streams/upgrade-guide.md
@@ -72,6 +72,8 @@ This release marks the General Availability for the core
functionality detailed
For more information about the feature set, design, usage and migration,
please refer to the [developer
guide](/{version}/streams/developer-guide/streams-rebalance-protocol).
+**Note:** Due to a critical broker-side bug in the offline migration code
([KAFKA-20254](https://issues.apache.org/jira/browse/KAFKA-20254)), we
recommend against doing migrations from classic to streams groups in 4.2.0.
Newly created streams groups are not impacted. Users planning to migrate should
upgrade their brokers to a later release that includes the fix.
+
### Other changes
Kafka Streams now supports Dead Letter Queue (DLQ). A new config
`errors.deadletterqueue.topic.name` allows to specify the name of the DLQ
topic. When set and `DefaultProductionExceptionHandler` is used, records that
cause exceptions will be forwarded to the DLQ topic. If a custom exception
handler is used, it is up to the custom handler to build DLQ records to send,
hence, depending on the implementation, the `errors.deadletterqueue.topic.name`
configuration may be ignored. `org.apache. [...]
