High Availability (HA)

A system design approach that ensures a high level of operational uptime and minimal downtime.

High Availability (HA) refers to a system design approach that ensures continuous operational performance for a specified period, typically measured as a percentage of uptime. A system with 99.99% availability (commonly called "four nines") allows for roughly 52 minutes of downtime per year.

HA is achieved through redundancy, failover mechanisms, and eliminating single points of failure. Common techniques include deploying applications across multiple servers or availability zones, using load balancers to distribute traffic, implementing health checks to detect failures, and automating failover to standby systems. Data replication across geographic regions adds further resilience.

API gateways are critical components in the request path, making their high availability essential. Edge-deployed gateways inherently provide HA by running across hundreds or thousands of points of presence worldwide. If one node fails, traffic is automatically routed to the nearest healthy node. Serverless API gateways on platforms like Cloudflare Workers benefit from this distributed architecture without requiring teams to manage failover configurations manually.