snat azure dns traffic in linux podsubnet azure and cilium scenarios to node ip

todo: snat windows podsubnet azure scenario to node ip
vnetscale scenarios (cilium and azure) already snat to node ip
roll out after cns iptables reconciliation goes in
cni still writes snat to primary ip but it is superseded by cns' rules

Author: QxBytes

cns/restserver/internalapi_linux.go

@@ -28,10 +28,6 @@ func (service *HTTPRestService) programSNATRules(req *cns.CreateNetworkContainer
 	service.Lock()
 	defer service.Unlock()
 
-	// Parse primary ip and ipnet from nnc
-	// in podsubnet case, ncPrimaryIP is the pod subnet's primary ip
-	// in vnet scale case, ncPrimaryIP is the node's ip
-	ncPrimaryIP, _, _ := net.ParseCIDR(req.IPConfiguration.IPSubnet.IPAddress + "/" + fmt.Sprintf("%d", req.IPConfiguration.IPSubnet.PrefixLength))
 	ipt, err := service.iptables.GetIPTables()
 	if err != nil {
 		return types.UnexpectedError, fmt.Sprintf("[Azure CNS] Error. Failed to create iptables interface : %v", err)
@@ -103,8 +99,8 @@ func (service *HTTPRestService) programSNATRules(req *cns.CreateNetworkContainer
 
 		// define all rules we want in the chain
 		rules := [][]string{
-			{"-m", "addrtype", "!", "--dst-type", "local", "-s", podSubnet.String(), "-d", networkutils.AzureDNS, "-p", iptables.UDP, "--dport", strconv.Itoa(iptables.DNSPort), "-j", iptables.Snat, "--to", ncPrimaryIP.String()},
-			{"-m", "addrtype", "!", "--dst-type", "local", "-s", podSubnet.String(), "-d", networkutils.AzureDNS, "-p", iptables.TCP, "--dport", strconv.Itoa(iptables.DNSPort), "-j", iptables.Snat, "--to", ncPrimaryIP.String()},
+			{"-m", "addrtype", "!", "--dst-type", "local", "-s", podSubnet.String(), "-d", networkutils.AzureDNS, "-p", iptables.UDP, "--dport", strconv.Itoa(iptables.DNSPort), "-j", iptables.Snat, "--to", req.HostPrimaryIP},
+			{"-m", "addrtype", "!", "--dst-type", "local", "-s", podSubnet.String(), "-d", networkutils.AzureDNS, "-p", iptables.TCP, "--dport", strconv.Itoa(iptables.DNSPort), "-j", iptables.Snat, "--to", req.HostPrimaryIP},
 			{"-m", "addrtype", "!", "--dst-type", "local", "-s", podSubnet.String(), "-d", networkutils.AzureIMDS, "-p", iptables.TCP, "--dport", strconv.Itoa(iptables.HTTPPort), "-j", iptables.Snat, "--to", req.HostPrimaryIP},
 		}