Hello everyone, I'm Pete. I'm fairly new to self-hosting and have been trying to tighten up my security posture, especially with all these containerized services I'm running. I've been reading the forum and the documentation, but I feel a bit lost on a fundamental point, and I was hoping for some patient, step-by-step guidance.

I'm working on the principle that an agent or service should have no network access unless explicitly granted. It seems like a good baseline. For many of my containers, I only want them to communicate on the loopback interface, `127.0.0.1`, and absolutely nothing else—no outgoing internet calls, no incoming requests from the LAN, nothing. But the default setups I see, whether in Docker examples or some application guides, often just expose ports to the host or worse, use `network_mode: host`. This feels like giving away too much from the start.

My main confusion is about the specific, concrete steps to implement a "deny all except loopback" rule as the default. I'm using Docker, and I know about `--network none`, but that seems to *completely* remove network, including loopback, which some applications need internally. I've read about `iptables` and `nftables`, and I've seen mentions of custom Docker networks, but I'm nervous about applying firewall rules incorrectly and breaking my host system or other containers. Could someone walk me through the safest, most straightforward method to achieve this?

For example, if I have a simple service like a database that should only be reachable by another container on the same host, what is the exact sequence of commands or configuration lines I should use? Should I create a custom bridge network first? Do I then apply a firewall rule inside the container, or on the Docker host? I'm particularly cautious about rules persisting after a reboot and not interfering with Docker's own `iptables` management. A detailed, ordered list of steps would be incredibly helpful for a beginner like me. Thank you so much for your time and expertise.