Can Couchbase XDCR achieve zero-downtime migration for small applications with RBAC-enabled buckets?

Zero-Downtime Migration with XDCR and RBAC

Couchbase's Cross-Datacenter Replication (XDCR) enables continuous data synchronization between clusters, supporting active-passive configurations for migration scenarios. For small applications requiring zero downtime, the replication lag and conflict resolution mechanisms become critical factors.

The N1QL querying language handles SQL-like operations on JSON documents, but index management during migration requires careful planning to maintain query performance. Couchbase Server 7.x introduced RBAC with granular permissions, which can complicate migration when user mappings differ between source and target environments.

Memory-optimized storage provides sub-millisecond latency but requires sufficient RAM allocation planning during cluster expansion. Bucket types—Couchbase, Ephemeral, and Memcached—have different persistence behaviors affecting migration strategy and data durability guarantees.

XDCR configuration complexity increases with network latency and security requirements, potentially introducing replication lag during migration. RBAC permission migration requires manual mapping of user roles and scopes between clusters to prevent access disruptions. Index rebuilds during cluster rebalancing can impact query performance until completion.

Key Questions:
1. What is the maximum achievable replication lag in XDCR when migrating RBAC-enabled buckets with active users?
2. How does Couchbase handle N1QL index synchronization during active-active XDCR configurations?
3. Can bucket type migration from Couchbase to Ephemeral storage occur without query performance degradation during replication lag?