Egress DNS: Get lowest TTL from the dns resolution chain

- Currently, we consider minTTL as lowest TTL among all available dns
'A' records and TTL for CNAME recs are ignored. This change will get
lowest TTL for the entire chain irrespective of the dns record type.

Author: Ravi Sankar Penta

pkg/network/common/dns.go

@@ -153,20 +153,20 @@ func (d *DNS) getIPsAndMinTTL(domain string) ([]net.IP, time.Duration, error) {
 
 		if in != nil && len(in.Answer) > 0 {
 			for _, a := range in.Answer {
+				if !ttlSet || a.Header().Ttl < minTTL {
+					minTTL = a.Header().Ttl
+					ttlSet = true
+				}
+
 				switch t := a.(type) {
 				case *dns.A:
 					ips = append(ips, t.A)
-
-					if !ttlSet || t.Hdr.Ttl < minTTL {
-						minTTL = t.Hdr.Ttl
-						ttlSet = true
-					}
 				}
 			}
 		}
 	}
 
-	if !ttlSet {
+	if !ttlSet || (len(ips) == 0) {
 		return nil, defaultTTL, fmt.Errorf("IPv4 addr not found for domain: %q, nameservers: %v", domain, d.nameservers)
 	}