#!/bin/sh

iptables -F

iptables -P INPUT DROP
iptables -P OUTPUT DROP
iptables -P FORWARD DROP

iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT

iptables -A INPUT -i eth0 -p tcp -m multiport --dports 22,80,443 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp -m multiport --sports 22,80,443 -m state --state ESTABLISHED,RELATED -j ACCEPT

iptables -A OUTPUT -o eth0 -p tcp -m multiport --dports 80,443 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -p tcp -m multiport --sports 80,443 -m state --state ESTABLISHED,RELATED -j ACCEPT

iptables -A OUTPUT -o eth0 -p udp -m multiport --dports 53 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -p udp -m multiport --sports 53 -m state --state ESTABLISHED,RELATED -j ACCEPT

iptables -A INPUT -j REJECT
iptables -A OUTPUT -j REJECT
iptables -A FORWARD -j REJECT

- Start from scratch
- Allow local traffic
- Allow incoming ssh, www traffic
- Allow outgoing www traffic
- Allow outgoing dns traffic
- Disallow all other traffic

docker run -p 5432:5432 postgres

psql -U postgres -h localhost

psql: server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.