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Use host's resolv.conf if no network namespace enabled

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My host system runs Fedora Silverblue 29 and I have NetworkManager's
`dns=dnsmasq` setting enabled, so my `/etc/resolv.conf` only has
`127.0.0.1`.

I also run my development podman containers with `--net=host`
for various reasons.

If we have a host network namespace, there's no reason not to just
use the host's nameserver configuration either.

This fixes e.g. accessing content on a VPN, and is also faster
since the container is using cached DNS.

I know this doesn't solve the bigger picture issue of localhost-DNS
conflicting with bridged networking, but that's far more involved,
probably requiring a DNS proxy in the container.  This patch
makes my workflow a lot nicer and was easy to write.

Signed-off-by: Colin Walters <walters@verbum.org>
This commit is contained in:
Colin Walters
2018-11-21 09:30:03 -05:00
parent 6df7409cb5
commit 870eed9378
2 changed files with 13 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
libpod/container_internal_linux.go
View File

@ -729,9 +729,10 @@ func (c *Container) generateResolvConf() (string, error) {
return "", errors.Wrapf(err, "unable to read %s", resolvPath)
}
// Process the file to remove localhost nameservers
// Ensure that the container's /etc/resolv.conf is compatible with its
// network configuration.
// TODO: set ipv6 enable bool more sanely
resolv, err := resolvconf.FilterResolvDNS(contents, true)
resolv, err := resolvconf.FilterResolvDNS(contents, true, c.config.CreateNetNS)
if err != nil {
return "", errors.Wrapf(err, "error parsing host resolv.conf")
}

12
pkg/resolvconf/resolvconf.go
View File

@ -103,13 +103,21 @@ func GetLastModified() *File {
}
// FilterResolvDNS cleans up the config in resolvConf. It has two main jobs:
// 1. It looks for localhost (127.*|::1) entries in the provided
// 1. If a netns is enabled, it looks for localhost (127.*|::1) entries in the provided
// resolv.conf, removing local nameserver entries, and, if the resulting
// cleaned config has no defined nameservers left, adds default DNS entries
// 2. Given the caller provides the enable/disable state of IPv6, the filter
// code will remove all IPv6 nameservers if it is not enabled for containers
//
func FilterResolvDNS(resolvConf []byte, ipv6Enabled bool) (*File, error) {
func FilterResolvDNS(resolvConf []byte, ipv6Enabled bool, netnsEnabled bool) (*File, error) {
// If we're using the host netns, we have nothing to do besides hash the file.
if !netnsEnabled {
hash, err := ioutils.HashData(bytes.NewReader(resolvConf))
if err != nil {
return nil, err
}
return &File{Content: resolvConf, Hash: hash}, nil
}
cleanedResolvConf := localhostNSRegexp.ReplaceAll(resolvConf, []byte{})
// if IPv6 is not enabled, also clean out any IPv6 address nameserver
if !ipv6Enabled {