Defines a group of servers. Servers can listen on different ports. In addition, servers listening on TCP and UNIX-domain sockets can be mixed. Example: upstream backend { server backend1.example.com weight=5; server 127.0.0.1:8080 max_fails=3 fail_timeout=30s; server unix:/tmp/backend3; server backup1.example.com backup; } By default, requests are distributed between the servers using a weighted r