proxy_bind

This directive appeared in version 1.9.2.

Makes outgoing connections to a proxied server originate from the specified local IP address. Parameter value can contain variables (1.11.2). The special value off cancels the effect of the proxy_bind directive inherited from the previous configuration level, which allows the system to auto-assign the local IP address.

The transparent parameter (1.11.0) allows outgoing connections to a proxied server originate from a non-local IP address, for example, from a real IP address of a client:

proxy_bind $remote_addr transparent;

In order for this parameter to work, it is necessary to run nginx worker processes with the superuser privileges and configure kernel routing table to intercept network traffic from the proxied server.