How does ZooKeeper manage node failures and recoveries?

ZooKeeper uses a heartbeat mechanism to detect when nodes become inactive or recover. Each node periodically sends a heartbeat to ZooKeeper, and if ZooKeeper does not receive the heartbeat from a node within a certain time frame, it will mark that node as inactive. Once a node is marked as inactive, ZooKeeper will trigger a Watcher event to notify clients that the node has become inactive.

Once the failed node is restored, it will resend a heartbeat to ZooKeeper, which will mark the node as recovered. This will trigger a Watcher event notification to inform clients that the node has been restored. Clients can then choose to reconnect to the recovered node as needed to maintain data consistency and availability.