failover to the next upstream server if one of the servers is slow

[itpp2012]

Can't tell atm. if a timeout forces a node to become offline but 60s is
still along time to wait (and decide) without actually knowing if a node is
overloaded (it might be just busy which does not always mean overloaded).

There are tools for fi. edge routers which polls a status page to decide to
change routing or not, in your case you first need to determine what exactly
the conditions are for a node to be slow and then design a way to detect
this, then you can look for tooling to automate whatever you want happening.

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,280259,280263#msg-280263