fix(dns): /etc/hosts was ignored by traefik

[kopax]

Fix traefik/traefik#6001

What does this PR do?

It create the missing /etc/nsswitch.conf.

Motivation

During proxying, traefik is performing a DNS resolution. This DNS resolution is skipping /etc/hosts file. This can cause unwanted DNS resolution, especially when using hostname as fqdn in marathon.

If you use /etc/hosts file for some resolution, this will fix it. If you use a real fqdn in marathon on a private network, you will still have to properly configure DNS serveur in traefik host.

[ldez]

Related to #42

[kopax]

I am curious, if this was already merged, why was it removed?

[kopax]

No clue why travis get this:

 ---> Running in d7c16a0f1158
OCI runtime create failed: container_linux.go:348: starting container process caused "exec: \"/bin/sh\": stat /bin/sh: no such file or directory": unknown
The command "./.ci/test.sh" exited with 1.

[dduportal]

• Build is failing on a sh error, because you updated a Docker image based on scratch (ref. https://hub.docker.com/_/scratch), which does NOT contains any sh or bash shell, resulting in failure of executing any RUN command. Suggestions proposed to fix this.
• Can you remove the comments, it's verbose and doesn't provide any value as all the history is kept in git and can be resolved with git blame
• Can add the commands to the alpine image please?

[kopax]

What command are required in the alpine image ? It seems they already have /etc/resolv.conf since you import them from another image.

[dduportal]

What command are required in the alpine image ? It seems they already have /etc/resolv.conf since you import them from another image.

• The scratch image copies files from the traefik:v*-alpine : there is a dependency so you must change the alpine change.
• The alpine image is built first. It does not have any nsswitch.conf file. So you have to create one. As Alpine has a sh binary within, you can totally use the same RUN command that you specified initially: RUN [ ! -e /etc/nsswitch.conf ] && echo "hosts: files dns" > /etc/nsswitch.conf
• Yes, there is already a file /etc/resolv.conf in the alpine image: this file is mounted by docker when container are run, providing the DNS resolvers to your container as explained in https://docs.docker.com/v17.09/engine/userguide/networking/default_network/configure-dns/ . Therefore this is out of the scope of your PR, since you request to use the /etc/hosts files before trying DNS resolution.

[kopax]

Thanks for providing all the details, I've updated the PR with requested change.

[dduportal]

Thanks, you're almost there.

I've added some suggestions, as Traefik's version comes from an environment variable for the templates (because it changes over time and we don't update all occurences by hand).

Once you'll have fixed the templates, can you run the following command from the root of the repository to update the Dockerfiles from templates please?

bash update.sh v2.1.1

[dduportal]

Side question: what is the status of this feature request for the Windows Docker images?

[dduportal]

Hi @kopax , can you ensure that you're setting the parent image to 2.1.1-alpine please? You can check the Travis-CI build logs, or run the command by yourself to reproduce the error on your local change.

[kopax]

Hi @dduportal too much time have passed since the traefik/traefik#6012 and I lost track of what is needed. What about the alpine image? Was this never fixed in recent traefik version? I am still running on 2.1.1 with this fix but perhaps it's time to close this?

[dduportal]

Hi @kopax , I am not involved anymore in the Traefik project. I would delegate to @ldez and @SantoDE to take care of your request instead :)