We should warn users who use the `--dns` command line option to point
DNS to a localhost address, either IPv4 or IPv6. Unless they have
specifically set up the container as a DNS server or are using
--net=host (which is why this should be allowed, but warned on because
those are pretty unique cases) a localhost address as a resolver will
not reach what they might expect (e.g. expecting it will hit localhost
on the Docker daemon/host).
Added a test for the message, and fixed up tests to separate stdout and
stderr that were using `--dns=127.0.0.1` to test the options.
Docker-DCO-1.1-Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com> (github: estesp)
Addresses #5811
This cleans up an error in the logic which removes localhost resolvers
from the host resolv.conf at container creation start time. Specifically
when the determination is made if any nameservers are left after
removing localhost resolvers, it was using a string match on the word
"nameserver", which could have been anywhere (including commented out)
leading to incorrect situations where no nameservers were left but the
default ones were not added.
This also adds some complexity to the regular expressions for finding
nameservers in general, as well as matching on localhost resolvers due
to the recent addition of IPv6 support. Because of IPv6 support now
available in the Docker daemon, the resolvconf code is now aware of
IPv6 enable/disable state and uses that for both filter/cleaning of
nameservers as well as adding default Google DNS (IPv4 only vs. IPv4
and IPv6 if IPv6 enabled). For all these changes, tests have been
added/strengthened to test these additional capabilities.
Docker-DCO-1.1-Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com> (github: estesp)
Only modifies non-running containers resolv.conf bind mount, and only if
the container has an unmodified resolv.conf compared to its contents at
container start time (so we don't overwrite manual/automated changes
within the container runtime). For containers which are running when
the host resolv.conf changes, the update will only be applied to the
container version of resolv.conf when the container is "bounced" down
and back up (e.g. stop/start or restart)
Docker-DCO-1.1-Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com> (github: estesp)
In that case /etc/resolv.conf will be generated with no search
option. Usage: --dns-search=.
Docker-DCO-1.1-Signed-off-by: Fabio Falci <fabiofalci@gmail.com> (github: fabiofalci)
