# It's common to forward the Host header to the backend.
proxy_set_header Host         $host;

# It's also common to set X-Real-IP with the $remote_addr of the connection.
proxy_set_header X-Real-IP    $remote_addr;

# X-Forwarded-{For,Proto,Host,Port} are typically proxied for reverse-proxy components
# to backends that support X-Forwarded-For parsing.
proxy_set_header X-Forwarded-For    $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto  $scheme;
proxy_set_header X-Forwarded-Host   $host;
proxy_set_header X-Forwarded-Port   $server_port;

# X-Forwarded-For is around AND still supported, but Forwarded is also an option
# It's not natively generated in NGINX, and not all backends support it,
# but it is a standard that is an alternative to X-Forwarded-*
proxy_set_header Forwarded          "by=hidden;for=$remote_addr;host=$host;proto=$scheme";

# Upgrade, Connection, and HTTP/1.1 are usually for websockets, which are becoming
# quite common.
proxy_set_header Upgrade            $http_upgrade;
# Note: $req_connection is defined in conf.d/http-upgrade_req-connection_map.conf
proxy_set_header Connection         $req_connection;  
proxy_http_version                  1.1;