To work with truly immutable filesystems, rather than ones
we sneakily remount `rw`, we are going to use overlay for
writeable containers. To leave the final mount as `rootfs`,
in the writeable case we make a new `lower` path for the read
only filesystem, and leave `rootfs` as a mount point for an
overlay, with the writable layer and workdir mounted as a tmpfs
on `tmp`.
See https://github.com/linuxkit/linuxkit/issues/2288
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
Unfortunately there are a lot of issues with resolv.conf as we
cannot actually write it into the image from any docker image, as docker will
always have something bind mounted in.
In addition, normally we expect the filesystem to br read only for images
that moby generates, so the actual etc/resolv.conf is likely not to be writeable.
Previously we were adding in a default resolv.conf into every image pointing at
Google's name servers but that is really a bad idea.
Instead, normal images now get an empty default, while images in the `init`
section will get a symlink, currently hard coded to `/run/resolvconf/resolv.conf`
but you can override this with the `files` section to be static or a different
link.
In future, if we have an easy way to build and extract images with user control
of this, we can drop this.
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
- this is pretty much the smallest change to split this out and it
exposes a few things that can be improved later
- no change to logging yet
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
