A container which sets up a simple iptables firewall only allowing outbound traffic to the docker local network and a single ip, port and protocol combination. Once the firewall is ready, a TCP socket is opened to signal the firewall is ready.

First, start the firwall container.

docker run \
  --name=firewall \
  --cap-add=NET_ADMIN \
  -e ALLOW_IP_ADDRESS=52.218.200.155 \
  -e ALLOW_PORT=80 \
  -e ALLOW_PROTO=tcp \
  0xcaff/simple-outbound-firewall

Then, connect another container to the firewall by sharing the firewall container's network stack.

docker run \
  --network="container:firewall" \
  -it \
  alpine:3.7

Checkout the example/ folder to see an example of this with docker-compose and waiting for the firewall to be ready before using the network.