upstream prematurely closed connection while reading response header from upstream
iptables -t nat -A PREROUTING -p tcp -m tcp -d PUBLIC_IP --dport 8001 -j DNAT --to-destination PROXY_IP:PROXY_PORT
curl -x PUBLIC_IP:8001 ifconfig.co -vvv
* Rebuilt URL to: ifconfig.co/
* Trying PUBLIC_IP...
* TCP_NODELAY set
...