As we've seen in the previous examples, exposing services living in containers to the outside world is a critical component of Docker. Up until this point, we've let the images and the Docker engine do the heavy lifting for us in terms of the actual port mapping. To do this, Docker uses a combination of metadata from container images as well as a built-in system for tracking port allocations. In this recipe, we'll walk through the process for defining ports to be exposed as well as options for publishing ports.
You'll need access to a Docker host and an understanding of how your Docker host is connected to the network. In this recipe, we'll be using the docker1 host that we used in previous recipes. You'll want to make sure that you have access to view iptables rules to verify netfilter policies. If you wish to download and run example containers, your Docker host will also need access to the Internet. In some cases, the changes we make may require...