dhcpcd-discuss

On 07/04/2020 08:17, Stéphane Veyret wrote:
> I spent a lot of time trying to use dhcpcd in namespaces. Maybe I did
> not do it correctly, but I feel there should be improvements in order
> to ease such usages.
>
> My use case is the following: I have a Docker container running. I
> added a (macvlan) interface in this container, connected to the
> physical host interface. Now I want to ask the DHCP server an address
> for the container.
>
> The problem is that the dhcpcd service is already started in the host,
> in order to provide address to the host interfaces. So, when I try to
> execute:
>
> nsenter -t 1234 -n dhcpcd container-eth0
>
> dhcpcd actually sends the request to the running master process, which
> does not see the container-eth0 interface and so is not working. What
> I had to do is stop the running service, then execute the namespace
> request, and restart the service.
>
> An evolution which seems simple to me and which would be very helpful
> would be a cli option to force dhcpcd to create a new process and not
> call the master, even if present (the contrary of --master).

So, if I understand the problem correctly the container 1234 sees the same root 
as the host? ie /var/run/dhcpcd on both point to the same location?

If the root is the same for both, what's your expectation with managing 
conflicts if say they receieve different DNS data for /etc/resolv.conf?

This might be as simple as not running the dhcpcd instance on the host in master 
mode - limit it to a single interface and do the same in your containers.

> There could be a more complex evolution to directly manage namespace
> in dhcpcd, so that the single master daemon would also see interfaces
> in provided namespaces. This could also be interesting as there may be
> multiple interfaces with same name in multiple namespaces, which would
> create conflict for the creation of the pid file.

Unlikely to happen, or at least not by me.

> What do you think? Does this make sense or am I mistaken?

I don't know anything about docker or namespaces or cgroups.
But I'll try and help.

Roy