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Cluster Mirroring synchronizes consumer group offsets from the source cluster to the destination cluster, enabling consumers to resume consumption from their last committed offset after failover. The MirrorMetadataManager periodically fetches consumer group committed offsets from the source cluster and replicates it to the destination cluster's. This ensures that consumer groups maintain their consumption progress across both clusters. During offset synchronization, the committed offset in the destination cluster may temporarily exceed the current log end offset (LEO) of the mirror topic. For example, if a consumer commits offset 100 in the source cluster but the destination cluster has only mirrored up to offset 80 (LEO = 80), the MirrorMetadataManager still commits offset 100 to the destination cluster. This is acceptable because the mirror leader continues fetching data and the LEO will eventually advance to include offset 100. However, if a failover occurs before the mirrored data catches up, consumers attempting to resume from offset 100 will receive an OffsetOutOfRangeException. To handle this scenario gracefully, consumers should configure auto.offset.reset=latest when consuming from mirror topics. This ensures that if a committed offset is beyond the current LEO after failover, the consumer automatically resets to the latest available offset rather than failing or resetting to the earliest offset.

Security Control

Cluster Mirroring supports comprehensive security controls through both authorization and authentication mechanisms. This ensures that only authorized principals can establish and manage cluster mirrors. When configuring a mirror, operators specify ACLs that should be synchronized from the source cluster, and these ACLs are periodically replicated to the destination cluster to maintain consistent access control policies across both environments.

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