DNSNameResolver

This is a CoreDNS plugin that works together with Kube-OVN to implement the FQDN Egress Firewall in Network Policy API.

The origin code comes from coredns-ocp-dnsnameresolver with following modifications:

• Change DNSNameResolver scope from namespaced to cluster to better implement Network Policy API.
• Remove DNS to IP mapping, using listers to simplify the logical.
• Remove plugin args.
• Update the build process to use community base images.
• Update dependencies.