Switch to newer detect-Docker-host-IP mechanism on Mac

[itamarst]

Currently on OS X we add a special IP alias to lo0 loopback interface, so that Docker containers can find the kubectl port-forward port when using --method container. Newer versions of Docker support a special DNS record docker.for.mac.localhost instead (this may obviate need for root, while we're at it.)

See https://docs.docker.com/docker-for-mac/networking/#use-cases-and-workarounds

We can't use this mechanism immediately since it's only present in absolute latest version of Docker, but eventually could switch.

[ark3]

Something like

docker run --rm -it --entrypoint "" $TELEPRESENCE_LOCAL_IMAGE nslookup docker.for.mac.localhost

should be pretty quick to query; the exit status is sufficient to know whether docker.for.mac.localhost is usable.

[ark3]

The latest (edge) release makes this a bit more complicated. The release notes say:

DNS name docker.for.mac.host.internal shoud be used instead of docker.for.mac.localhost (still valid) for host resolution from containers, since since there is an RFC banning the use of subdomains of localhost (See https://tools.ietf.org/html/draft-west-let-localhost-be-localhost-06).

[ark3]

Newest release notes say

DNS name host.docker.internal shoud be used for host resolution from containers. Older aliases (still valid) are deprecated in favor of this one.

[ark3]

If they ever fix docker/for-linux#264, we could avoid the route -n nonsense entirely.

[ark3]

Fixing this will move us closer to Windows support for the container method.

[duizendnegen]

Indications for possible solutions are https://dev.to/bufferings/access-host-from-a-docker-container-4099

[ark3]

Telepresence 0.95 includes #726, and thus does not try to connect to the host from within the container. As such, this is no longer an issue. Closing.