This script is intended to handle Docker iptables port-forwardings manually, for those times when you can't let Docker manage iptables on its own because it conflicts with other things on the system that are also trying to manage iptables.

• systemd is your init and containers will be managed by systemd .service units.
• Canonical source for iptables rules is /etc/iptables.d/ and /etc/ip6tables.d/
• A service named iptables.service exists and when stated or restarted will flush all running iptables rules and reload rulesfrom the .d directories.

1. The docker daemon should be configured to start with --iptables=false.

2. Create an /etc/iptables.d/10_docker file with the following rules. These are the base rules that would normally get created when the docker daemon is started. NOTE: You must use a chain name other than DOCKER because even with --iptables=false docker will remove this chain on startup (bug in docker?).

    *nat
    :DOCKER_CONTAINERS - [0:0]
    -A PREROUTING -m addrtype --dst-type LOCAL -j DOCKER_CONTAINERS
    -A OUTPUT ! -d 127.0.0.0/8 -m addrtype --dst-type LOCAL -j DOCKER_CONTAINERS
    -A POSTROUTING -s 172.17.0.0/16 ! -o docker0 -j MASQUERADE
    COMMIT
    *filter
    -A FORWARD -o docker0 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
    -A FORWARD -i docker0 ! -o docker0 -j ACCEPT
    -A FORWARD -i docker0 -o docker0 -j ACCEPT
    COMMIT
   

3. ExecStartPost= and ExecStopPost= commands in each docker container .service:

    [Unit]
    Description=hello-world docker service
    After=docker.service
    Requires=docker.service
   
    [Service]
    SyslogIdentifier=hello-world
    ExecStartPre=-/usr/bin/docker rm hello-world
    ExecStart=/usr/bin/docker run  --name="hello-world" --publish="5000:5000" --rm=true quay.io/getpantheon/hello-world:master
    ExecStartPost=/opt/titan/utilities/docker/docker-iptables.py create hello-world
    ExecStop=-/usr/bin/docker stop hello-world
    ExecStopPost=/opt/titan/utilities/docker/docker-iptables.py delete hello-world
    Restart=always
    RestartSec=10s
    TimeoutStartSec=120
    TimeoutStopSec=15
   
    [Install]
    WantedBy=multi-user.target
   

The script can also be run against any running container:

docker-iptables.py create container-name
docker-iptables.py delete container-name

The above commands will read the port mappings from docker inspect of the running container and add or delete the rules from /etc/iptables.d. It will also call systemctl restart iptables.service to load or remove the rules from the running config.

1. run unit tests: python setup.py test
2. run pylint test: pylint docker_iptables.py

1. Do work in a branch
2. Add tests, ensure tests pass on Circle
3. Bump version in setup.py in your branch
4. Send PR to master branch