Add nsswitch.conf file into the image

[mprasil]

This fixes an issue I've encountered - the absence of /etc/nsswitch.conf makes traefik ignore the /etc/hosts file inside the container. For reference see here and here for alpine.

This is very surprising and often painful in some scenarios like this one. But I suppose any user that is trying to use --add-host docker flag in lieu of DNS entry for whatever reason is going to be burned by that.

The nsswitch.conf file added is default configuration found in most distributions I've seen. I've used it for completeness as that's the one distroless base image is using, but just having this one line in would alleviate the specific problem:

hosts:          files dns

I can modify the PR if you prefer that format.

Hope that helps.

[dduportal]

Hi @mprasil , thanks for this proposal.

Could you update this PR to fit https://github.com/gliderlabs/docker-alpine/issues/367#issuecomment-424546457 (tianon being a maintainer/reviewer of the official Docker Library, his fix sounds like a solid pattern for the reviews)?

It means:

• Removing the nsswitch.conf files (and the related COPY/ADD instructions from the PR
• Adapting the tmpl.Dockerfile with the RUN instruction for the nsswitch.

[mprasil]

Hi @dduportal, I've updated the PR and rebased on top of current master. Hopefully it's better now.

[mprasil]

Resolved merge conflict.