backup directive, The Nginx documentation states rather minimally:
marks the server as a backup server. It will be passed requests when the primary servers are unavailable.
What if you have multiple backups and the primary server goes down, is one of the backups appointed the new primary? Or will Nginx Round Robin between them?
I have a primary server and multiple backups, but all connections should always go to the same primary or backup. Sort of like the ip_hash load balancing mode except it should use the same server for all connections and clients.