High availability identity is the guarantee that user authentication and authorization never fail, even when parts of your system do. It is not a single product. It is an architecture. It is the practice of removing single points of failure in identity services. If login breaks, your app is broken. Everything else follows from that truth.
A high availability identity solution handles traffic spikes, hardware failures, and network partitions without downtime. This means redundant identity providers, distributed databases, synchronized session stores, automated failover, and consistent health checks. No single node, region, or connection can become a bottleneck.
Design starts with split-brain prevention and ends with globally consistent state. Use multi-region clusters for your identity provider. Keep authentication tokens valid across failover. Cache permissions and profiles close to your compute. Always use secure replication channels. Measure and enforce low latency between identity nodes in every region you support.