This Nginx HTTP module provides only one variable $proxy_peer_host which is similar to variable $proxy_host from Nginx HTTP proxy module. While the latter variable contains the name of the upstream which a client request is being proxied to, variable $proxy_peer_host contains the name of the actual server inside the upstream given it was configured in directive upstream.

Let's test a simple configuration.

user nobody; worker_processes 1; events { worker_connections 1024; } http { default_type application/octet-stream; sendfile on; upstream u1 { server 127.0.0.1:8080; server localhost:8080; } server { listen 8010; server_name main; location /u1 { proxy_pass http://u1; echo_after_body "[u1] proxy_peer_host: $proxy_peer_host"; echo_after_body " proxy_host: $proxy_host"; } } server { listen 8080; server_name backend; location / { return 200; } } }

The value of $proxy_peer_host must rotate in a round-robin manner when we do sequential HTTP requests to location /u1.

$ curl 'http://localhost:8010/u1' [u1] proxy_peer_host: 127.0.0.1:8080  proxy_host: u1 $ curl 'http://localhost:8010/u1' [u1] proxy_peer_host: localhost:8080  proxy_host: u1 $ curl 'http://localhost:8010/u1' [u1] proxy_peer_host: localhost:8080  proxy_host: u1 $ curl 'http://localhost:8010/u1' [u1] proxy_peer_host: 127.0.0.1:8080  proxy_host: u1

Variable $proxy_peer_host can be used in directive proxy_ssl_name to verify names of backend servers against the names given in directives server inside the upstream rather than the name of the upstream itself.