detect and adapt to system DNS and network/VPN changes at runtime

[TheIndifferent]

The ugly workaround I've submitted to TheNewNormal/corectl.app#21 works, but would be much better to have that in corectld itself.

Use-case is the following:

• corectld starts in home network with local DNS 192.168.1.1 to resolve hostnames from local network.
• VPN connection is established to restrictive office network, /etc/resolv.conf is updated with new DNS 10.11.12.13, to resolve internal docker images registry (which is not available for public) registry.mycompany.net.

Currently I have to restart the corectld every time VPN connection drops or established again, which also means that VM restarts and all containers are stopped.

Would be great to have dynamic refresh of resolv.conf from inside corectld, so new DNS will be used - even if with some delay - but without restarting.

[AntonioMeireles]

we'll try to integrate what you want together with transparent handling of VPN interfaces.

[TheIndifferent]

Small update: found out that skydns will read nameservers from /etc/resolv.conf if none specific, that worked (deleting this line: https://github.com/TheNewNormal/corectl/blob/golang/components/server/dns.go#L63 ). But now another showstopper appeared, search domains. VirtualBox made it seem so easy, just set to use host DNS resolver for NAT and everything magically works, but digging into it suddenly there are so many corner cases...

[rbellamy]

I'm not sure if this is related to an issue I'm having, since I'm still learning the intricacies of coreos + kubernetes, let alone corectl.

My pods can resolve external DNS queries just fine, but cannot resolve those DNS requests that require our internal DNS server (we use split DNS VPN tunnels via Cisco AnyConnect).

DNS queries for private addresses run on the host resolve internal addresses just fine.
DNS queries for private addresses run on k8solo-01 or in any of the pods, fail to resolve.

Mac OS X El Capitan

2016-10-03 04:06:10
rbellamy@terraspark i ~/Development/Terradatum/aergo/aergo-client feature/docker % nslookup
> aergo.dev.terradatum.com
Server:     10.1.1.245
Address:        10.1.1.245#53

Non-authoritative answer:
Name:   aergo.dev.terradatum.com
Address: 10.1.1.146

k8solo-01

core@k8solo-01 ~ $ nslookup
> server 10.1.1.245
Default server: 10.1.1.245
Address: 10.1.1.245#53
> aergo.dev.terradatum.com
Server:     10.1.1.245
Address:        10.1.1.245#53

** server can't find aergo.dev.terradatum.com: NXDOMAIN

Neither can I ping the internal DNS server from k8solo-01

core@k8solo-01 ~ $ ping 10.1.1.245
PING 10.1.1.245 (10.1.1.245) 56(84) bytes of data.
^C
--- 10.1.1.245 ping statistics ---
5 packets transmitted, 0 received, 100% packet loss, time 4004ms

So perhaps this is more a routing issue than a DNS issue - should the DNS server at 192.168.64.1 be able to resolve any query that my Mac OS X can resolve?

[databus23]

Whats the status of this issue? It seems to me right now corectld does not consider /etc/resolv.conf at all. It defaults to public nameservers from google (8.8.8.8 and 8.8.4.4) and thats it.
This is not working well for environments where public dns servers are not reachable.

I'm hitting a wall trying to use corectl.app which starts corectld with static parameters and no good way to add --recursive-nameservers.

Issue TheNewNormal/corectl.app#21 is basically what I want but it was closed with a reference to this issue.

[AntonioMeireles]

@databus23 just reopened TheNewNormal/corectl.app#21. Thanks for reporting!