The `--userland-proxy` daemon flag makes it possible to rely on hairpin NAT and additional iptables routes instead of userland proxy for port publishing and inter-container communication. Usage of the userland proxy remains the default as hairpin NAT is unsupported by older kernels. Signed-off-by: Arnaud Porterie <arnaud.porterie@docker.com> Upstream-commit: f42348e18f73d1d775d77ac75bc96466aae56d7c Component: engine