as specified by the haproxy documentation: https://www.haproxy.org/download/1.8/doc/proxy-protocol.txt only protocol v1 is implemented for now, protocol v2 is binary, and will be implemented in the future. the proxy protocol allows the destination/target to know the address/port of the client connectiing. in nginx it's supported by enabling the `proxy_protocol` parameter to the `listen` directive.