High availability (HA) refers to a system's ability to run continuously without failing for a designated period, ensuring service reliability through scalability, redundancy, and failover mechanisms. Businesses need HA systems to reduce downtime and revenue loss, as well as ensure uninterrupted service delivery in today's digital economy. High availability architecture is built on the principle of having redundancy and failover mechanisms, including clustering patterns such as active-passive and active-active setups. Clustering groups multiple servers or nodes to operate as one system, improving performance and enabling minimal downtime. Cloud computing's distributed infrastructure helps with high availability by relying on scalability, redundancy, and replication, automated resource management within the cloud, and geographic distribution to sidestep any disruptions. HA systems require operational procedures, such as regular data backups and testing recovery processes, to maintain uptime and continuous service delivery. The cost-benefit ratio of high availability can be measured, with long-term benefits including increased reliability, customer retention, and a competitive edge. Key metrics to track include mean time between failures (MTBF) and mean time to recovery (MTTR), while operational best practices include identifying single points of failure, planning for failure, and implementing failover mechanisms. High availability solutions can be tailored to meet business needs, with Aerospike offering HA capabilities that enhance application availability and resilience. By combining redundancy, replication, load balancing, scalability, geographical diversity, health checks, and failover systems, HA creates a continuous, reliable system, such as an e-commerce platform using redundant servers and replicated databases.