Rebalance is a critical component of Couchbase architecture that allows for online cluster management operations, including adding/removing nodes, online upgrades of hardware or software, and recovery after node failure. In Couchbase Server 6.5, rebalance has been made more robust, manageable, and faster through various improvements, including automatic retries for failed rebalances, auto-failover during rebalance, and improved rebalance progress monitoring. The new features aim to reduce the impact on front-end applications and improve performance, especially with larger data sets. Additionally, a rebalance report can be obtained through the REST API, providing detailed information about the last rebalance process.