I have set up a bastion server (A) that acts as the only "hallway" to enter a bunch of other private VPS's (B). That is to say: the private machines only accept SSH-connections from (A) on a non-standard port, which is a hard firewall rule, and only accept these connections from (A) using a specific user and a specific key.
I was wondering which strategy I should use for emergencies where for instance the bastion (A) goes down, gets compromised or in somehow gets useless. It would make my private VPS's (B) inaccessible for ever.
Should I allow for the (B) machines to be accessed through another IP address than the bastion (A) as well? I don't have the infrastructure to allocate whole IP blocks, so permissions based on ranges won't work for me.