Assumptions – Two servers, one active and one backup hot and fully replicated. You want uninterrupted service to LAN, internal users, internet, whatever.
Cisco supports ‘fallover’, request that is not answered by the normal PORT is automatically transferred to the backup PORT.
Implementation is a function the switch/router and which version of IOS you are running.
I realize this is a generic answer, but your question without details is very generic. Good luck