Failover is a principle of automatic switchover to a backup service when the main service is no longer available.
Applied to the DNS, the Failover service consists of monitoring DNS Resources Records and switching to a backup record if the main record is no longer available. During the switch, the main record continues to be monitored and when it is available again, a switch back to normal is operated.
Surveillance is carried out by a set of probes distributed over different networks and worldwide geographical locations. The failover rules are defined upfront, whether it is a number of iterations or a period of time between availability checks.
The customer is informed of the changeover by an email alert, he is also informed of the return to normal.