Hi Jean-Marc, The Kafka connector for Flink 2.x is already available starting with the Flink Kafka Connector 4.0.0 release, which is compatible with Flink 2.0.x. So if you plan to upgrade to Flink 2.x, you should use the 4.x line of the connector.
Regarding state compatibility, Flink 2.x introduces an upgrade of Kryo from 2.24.0 to 5.6.2. This can potentially break compatibility for any state serialized using Kryo. However: - If your application state is based on POJOs, Avro, Protobuf, or custom TypeInformation serializers, it should remain compatible. - Only operators or state that explicitly rely on Kryo serialization (e.g., types not covered by Flink’s type system and falling back to Kryo) may face compatibility issues. To check whether Kryo is used in your state: 1. Run your application with the config option -Dexecution.checkpointing.unaligned.enabled=false -Dexecution.savepoint.serializer-check=VERBOSE or use the state.checkpoints.dir inspection tool to print serializers. 2. Look for log lines mentioning KryoSerializer — if none appear, your state should be safe to migrate. If Kryo is used, you’ll likely need to take a full stop-and-restore migration: - Export data from the current state - Deploy the Flink 2.x job with a clean state, then reload data For most typical use cases that don’t rely on Kryo, Flink’s built-in savepoint compatibility will allow restoring from 1.20.x to 2.0.x without issues. BR, G On Tue, Oct 28, 2025 at 5:57 PM Jean-Marc Paulin <[email protected]> wrote: > Hi, > > We are currently using Flink 1.20.3 with the kafka connector and are > planning to upgrade to Flink 2.x for our streaming application. > > Do you have an estimated timeline for when the Kafka connector will be > available for Flink 2.x releases? > > Additionally, with the upgrade of Kryo from 2.24.0 to 5.6.2 in Flink 2.x, > we are concerned about state compatibility. Will a Flink 2.x streaming > application be able to resume from a 1.20.3 application state? Is there a > method to determine if our existing application state has a dependency on > Kryo that would prevent a smooth upgrade? > > Thanks, > > JM >
