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jpetazzo / pipework

Software-Defined Networking tools for LXC (LinuX Containers)
Apache License 2.0
4.22k stars 727 forks source link

dhcpcd empties resolv.conf on the host #104

Closed jeroenpeeters closed 9 years ago

jeroenpeeters commented 9 years ago

Thanks for creating this handy script! Unfortunately I have one issue preventing me from using it successfully. I run Docker on a CoreOS cluster which has dhcpcd installed. Assigning an IP from DHCP to a docker container is successful the first time. However, I discovered that dhcpcd also writes to /etc/resolv.conf on the host machine. It basically empties the file, and leaves a comment stating that dhcpcd changed the file.

My understanding is that ip netns exec would allow the execution of a namespace unaware application in the namespace. Still it seems that dhcpcd is able to "break out" of the namespace and change the configuration of the host machine.

Do you have any pointers for me how to prevent this?

[ $DHCP_CLIENT = "dhcpcd" ] && ip netns exec $NSPID $DHCP_CLIENT -q $CONTAINER_IFNAME -h $GUESTNAME

jpetazzo commented 9 years ago

Yes, unfortunately, with the current mode of operation, this is unavoidable. In a future version of pipework, the DHCP client will execute in a separate container sharing the same namespace, which will avoid the issue (but not completely solve the resolv.conf update by the DHCP server).

ehooi commented 9 years ago

I also meet this problem. And I avoid the problem by adding option -C resolv.conf to dhcpcd. ip netns exec "$NSPID" "$DHCP_CLIENT" -q "$CONTAINER_IFNAME" -h "$GUESTNAME" -C resolv.conf I think make this option default is ok for almost all situation.

jpetazzo commented 9 years ago

The DHCP client now executes in a separate container; that should fix the problem :-)