libnetwork, Network: add field NetworkDNSServers for network scoped dns

[flouthoc]

libnetwork must allow to pass network_dns_servers so aardvark and netavark can consume it and enabled network scoped dns.

Feature implemented at netavark and aardvark end

• Netavark: aardvark, netavark: support network scoped dns via network_dns_servers netavark#497

[flouthoc]

@containers/podman-maintainers @Luap99 @mheon PTAL

[Luap99]

Since this field can only be set on network create you should validate it there.
a) make sure it only contains ips
b) it is only set when DNSEnabled is true
c) in the cni backend it should error out since we will not support it there.

And then don't forget to add tests for it.

[flouthoc]

Since this field can only be set on network create you should validate it there. a) make sure it only contains ips b) it is only set when DNSEnabled is true c) in the cni backend it should error out since we will not support it there.

And then don't forget to add tests for it.

@Luap99 Did you mean validations in NetworkCreate API in libnetwork or the command podman network create we usually validate parsing details and types at frontend so should test be at the podman end ? I think we can add validation to both NetworkCreate at libnetwork and podman cli end.

[Luap99]

Validation should always be done in the backend in libnetwork.

[flouthoc]

@Luap99 SGTM.

One note though some of the validation and parse checks are being made at frontend like https://github.com/containers/podman/blob/main/cmd/podman/networks/create.go#L137 maybe we should move these to backend later on then for consistency.

[Luap99]

One note though some of the validation and parse checks are being made at frontend like https://github.com/containers/podman/blob/main/cmd/podman/networks/create.go#L137 maybe we should move these to backend later on then for consistency.

If you look at the Network format struct these checks only make sense in the frontend. It is impossible to set a gateway without subnet in the type so the cli has to validate the flags.

[Luap99]

LGTM, but I guess we want the nv/av PRs to merge first?

[openshift-ci]

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[flouthoc]

@Luap99 Upto you and maintainers but I think this can go in as-is cause this PR is not blocked on nv/av. Podman and nv/av are just gonna use this.

[rhatdan]

/lgtm

[flouthoc]

Once Upstream nv/av PR gets merged I'll wire this into podman.