currently this is my setup at datacenter,
datacenter connection-> my Cisco router -> Linux server(1 Dell poweredge)

Basically i would like to have 2 cisco router, one is reserved for backup incase the main cisco router is down, and 2 server

connected to switch, switch will goto 2 Dell poweredge server,
the production serverA will running the application,webserver,databases.

while serverB will just doing the backup for serverA from time2time. Incase serverA is down, we will manually plug the connection to ServerB to continue running

will this work, or is this the correct way to keep my application up 24/7 all the time? What else do we need ?