Couchbase Server 5.0 introduces Index Replicas, a significant improvement over the previous system of Equivalent Indexes used in version 4.x, which required manually creating identical indexes with different names to ensure high availability and load balancing of N1QL queries. Index Replicas simplify this process by allowing users to specify the number of replicas or the nodes on which they should be placed, and Couchbase automatically manages query traffic distribution and rebalancing when nodes are added or removed. This approach ensures that indexes remain online even during system failures, as any failed index scan can be redirected to another replica. The system supports both Memory-Optimized Indexes (MOI) and Global Secondary Indexes (GSI) under the Plasma engine, enhancing reliability and ease of management compared to the manual operations required for Equivalent Indexes, while all replicas remain active to aid in load balancing. Users can also manually distribute replicas using the 'nodes' parameter and can move replicas between nodes using a specific REST call, ensuring flexibility and control over the indexing environment.