DNS failover is a mechanism used to ensure high availability and reliability of internet services by automatically redirecting traffic from a failed server to a functional one. When a server or service becomes unavailable due to hardware failure, network issues, or other reasons, DNS failover detects the failure and updates the DNS records associated with the affected domain name to point to an alternate server or location.

Here's how DNS failover typically works:

1. Monitoring: A monitoring system continuously checks the health and availability of servers and services by sending periodic requests and analyzing responses. If a server fails to respond or returns an error, the monitoring system detects the failure.
2. Failover Trigger: Upon detecting a failure, the monitoring system triggers the failover process, which involves updating DNS records to redirect traffic away from the failed server.
3. DNS Record Update: The DNS records associated with the domain name are dynamically updated to point to an alternate server or location that is still operational and capable of handling the traffic.
4. TTL (Time-to-Live) Management: DNS failover systems often adjust the TTL of DNS records to control how quickly changes propagate across the DNS infrastructure. By reducing the TTL, the failover can take effect more quickly, ensuring minimal downtime.
5. Traffic Redirection: Once the DNS records are updated, subsequent DNS queries for the affected domain name are directed to the alternate server or location, allowing users to access the service without interruption.

DNS failover is commonly used in scenarios where downtime can have significant consequences, such as e-commerce websites, online applications, and critical business services. By automatically redirecting traffic in the event of a server failure, DNS failover helps minimize service disruptions and ensures a seamless user experience.

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