DNSFailovers

DNS failover, or DNS-based failover, is a resilience technique that uses the domain name system to redirect client requests away from an unhealthy origin to a healthy backup by updating DNS records when a monitored endpoint fails. It leverages automated health checks, a DNS provider capable of rapid record changes, and TTL settings to control how quickly clients may switch to alternate servers.

Operation typically involves a primary endpoint and one or more backups. The system runs periodic health checks on the primary. If a failure is detected, the DNS provider updates the domain’s records to point to the backup endpoint. When the primary recovers, records are switched back. Propagation depends on DNS caching and TTL values, which should be tuned to balance responsiveness with stability.

Benefits include simplicity, no changes to applications, and work with legacy clients that resolve via DNS. It can provide regional failover and disaster recovery at relatively low cost. Limitations include latency introduced by DNS caching, potential for stale traffic during TTL, and lack of instantaneous failover. It also requires stateless backends or external session management and depends on the DNS provider for reliability and security.

Best practices involve using moderate TTL values (for example 60 to 300 seconds), deploying health checks for all critical endpoints, and combining DNS failover with other routing mechanisms such as CDNs or load balancers for faster recovery. Security considerations include protecting DNS records against spoofing and enabling DNSSEC where available.