Database cluster administration involves managing a group of interconnected databases to ensure availability, scalability, and fault tolerance. Key tasks include configuring nodes, balancing loads, managing replication, and ensuring high availability through failover mechanisms. Security in database clusters focuses on encryption, access controls, authentication, and ensuring data integrity across nodes. Administrators also monitor cluster performance and address issues like latency or hardware failures. Regular backups, updates, and patching are essential to maintaining cluster security and stability.