Secure Docker with iptables firewall and Ansible

Out of the box, security with Docker (and Docker Swarm) over the network is bad. Okay, that’s not entirely true. Out of the box when you have no containers started, it’s fine. But after you start a container, and if you publish a port, they are exposed to the outside world by default. And it’s not easy to fix. You need to create a custom Docker firewall with iptables.

Docker and the iptables INPUT chain

When testing Docker and iptables I stumbled upon something interesting. It appears Docker uses the iptables INPUT chain in an undocumented way. Well that’s interesting..

Find Version Tag for Latest Docker Image

If you’ve ever used Docker, you’ve probably used the latest Docker image tag. This is bad. Do not do this! You will be in a situation where you need to find what version you were actually using. This is how you can find the version of that “latest” image you have running.

Dockerfile ARG FROM ARG trouble with Docker

Dockerfile ARG

Using a dynamic Dockerfile can have great benefits when used in your CI/CD pipeline. You can use the ARG statement in your Dockerfile to pass in a variable at build time. Even use a variable in the FROM statement!