Publishing container ports is insecure by default. Meaning, when you publish a container's ports it becomes available not only to the Docker host, but to the outside world as well.

If you include the localhost IP address (127.0.0.1) with the publish flag, only the Docker host can access the published container port.

docker run -p 127.0.0.1:8080:80 nginx

DNS Services

By default, containers inherit the DNS settings of the host, as defined in the /etc/resolv.conf configuration file. Containers that attach to the default bridge network receive a copy of this file. Containers that attach to a custom network use Docker's embedded DNS server.