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Stretched clusters are not suitable for DR scenarios because they provide no protection against software failures, configuration errors, and accidental topic deletions. Vendors that recommend stretched cluster deployments typically position them for high availability (HA) rather than DR, and notably, most do not offer stretched clusters as a managed service option, further underscoring the operational challenges and limited DR effectiveness of this architecture.

Proposed Changes

A cluster mirror is a named, unidirectional replication channel from a remote source cluster to the local destination cluster. It is created by specifying a unique mirror name along with the source cluster's bootstrap servers and security credentials. Once a mirror is created, individual topics on the source cluster can be started, stopped, or paused for replication within it. Each mirror is a first-class entity managed through the Admin API and the kafka-mirrors.sh CLI tool, with its state persisted in a new Kafka's internal coordinator that manages cross-cluster replication.

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The architecture consists of three primary main components that work together to provide automatic metadata synchronization and data replication. The following diagram illustrates how these components are wired together. For the sake of clarity, some internal APIs are excluded.

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The mirror name is stored as a topic-level internal configuration called mirror.name that has the same validation rules of topic names, and propagates through Kafka's metadata log as configuration change records. When topics are added to a mirror, the quorum controller generates configuration metadata records that are replicated to all brokers through the standard metadata update mechanism. Brokers monitor these configuration changes to detect when partitions they lead belong to a mirror, triggering the creation of mirror fetchers and enforcement of read-only semantics. This design ensures that mirror associations are visible, auditable, and manageable through standard Kafka tools while maintaining strict control over how mirroring relationships are established and modified.

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