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2025-03-17 - Connect Docker to Localhost

If you want to connect docker to access any port on your computer's localhost, here is what worked for me.

When you start your container, use the `--add-host` option.

Running that command, you can see that the /etc/hosts file was populated with a host.docker.internal line:

The `host.docker.internal` part is customizable, you can make it `localhost` or anything you want. Use that hostname in your application to communicate to localhost. And `host-gateway` is what refers to localhost.

Here is an example, curling an http web server on localhost:

Initially, the above command would hang for me. I needed to configure my UFW firewall. It blocks local ip ranges by default, so after some investigation with wireshark, I added this firewall rule.

Maybe there is a better/more targeted way to update your firewall. But that's what worked for me. I'm not the best with networking and it's hard to find stuff like this on the internets.

If you need to investigate similar firewall issues with UFW, you could try disabling your firewall and running wireshark to investigate. Here are useful commands if you find yourself in a similar situation: