Script to set up port redirection and disable it again. The tricky thing here is that even when you disable the port redirect, traffic can still flow through the redirected port for already established socket sessions, but new connections can't be established. This, in addition to removing the redirect, gdbs into the process and closes the file …

resiliency.sh

#!/bin/bash

if [[ -z $1 ]]; then
  echo -e "\x1b[31mMust supply src + dest port"
  exit 1
fi

echo -e "\x1b[32mForwarded port $2 --> $1\x1b[33m"
sudo iptables -t nat -I OUTPUT -p tcp -o lo --dport $2 -j REDIRECT --to-ports $1

read -e -p "Hit enter to kill port redirect.."

echo "Killing iptables forward.."
sudo iptables -t nat -D OUTPUT 1

PID=$(ps aux | grep -i [r]ails | awk '{print $2}')
FD=$(sudo lsof -p $PID | grep $2 | awk '{print $4}')

if [[ -z $FD ]]; then
  echo -e "\x1b[31mNo FD found"
  exit 1
fi

echo "p close($FD)" | sudo gdb -p $PID