Sorry, my bad, capturing traffic send from the haproxy to the backend actually contains the X-Forwarded-For header. Simply close my request and thanks for the quick answer / interaction.

You're right, headers for port and protocol are being added but not the host.

Well, it could be an option in the load-balancing haproxy service definition, something like "option forwardedfor" that would enable the http header and feed it with real client IP.