docker run --add-host=NAME:host-gateway does not work

[yrashk]

Describe the bug

When trying to use the add-host feature from Docker, I get an nil entry in /etc/hosts inside of the container

Steps To Reproduce

Steps to reproduce the behavior:

1. docker run -ti --add-host=test:host-gateway ubuntu:latest
2. cat /etc/hosts
3. It will contain

<nil>    test

Expected behavior

/etc/hosts should contain a mapping between host's IP and test

Notify maintainers

@offline @tailhook @vdemeester @periklis @mikroskeem @maxeaubrey

Metadata

 - system: `"x86_64-linux"`
 - host os: `Linux 5.15.86, NixOS, 22.11 (Raccoon), 22.11.1421.e9ade2c8240`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.11.1`
 - channels(root): `"nixos-22.11.1421.e9ade2c8240"`
 - channels(yrashk): `"nixos-unstable-23.05pre439706.9813adc7f7c, release-22.11.tar.gz-22.11"`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixos

[mikroskeem]

This sounds like upstream bug?

[yrashk]

I have it working on Ubuntu, macOS, etc. That's what I thought it may be something NixOS specific, but I can't put my finger on it just yet.

[NateWright]

I am also having this issue.

[mikroskeem]

Does this issue still appear?

Built a system using nixos-22.11 channel (7dc71ae), Docker version 20.10.21, and I couldn't reproduce this:

[root@docker-playground:~]# docker run --rm -ti --add-host=test:host-gateway ubuntu:latest
root@f5913104e560:/# cat /etc/hosts
127.0.0.1	localhost
::1	localhost ip6-localhost ip6-loopback
fe00::0	ip6-localnet
ff00::0	ip6-mcastprefix
ff02::1	ip6-allnodes
ff02::2	ip6-allrouters
172.17.0.1	test
172.17.0.2	f5913104e560

[NateWright]

I am running the same versions and do see test mapped in. I can ping test but I cannot curl a website running on the host.

[mikroskeem]

Do you have firewall enabled but Docker interface not added into networking.firewall.trustedInterfaces?

[NateWright]

That does fix the issue. Thank you

[mikroskeem]

I suppose that this problem has disappeared and issue can now be closed.

[Naim-Bijapure]

I have faced this issue.
this is a firewall-related issue. if anyone facing this issue you can disable the firewall.
networking.firewall.enable = false; ( not a good practice :) )