List exact DNS entries for a requested bucketName (#6936)

Currently we would end up considering common prefix
buckets to be part of the same DNS service record,
which leads to Minio server wrongly forwarding the
records to incorrect IPs.

pkg/dns/etcd_dns.go

@@ -85,16 +85,28 @@ func (c *coreDNS) list(key string) ([]SrvRecord, error) {
 		}
 		srvRecord.Key = strings.TrimPrefix(string(n.Key), key)
 		srvRecord.Key = strings.TrimSuffix(srvRecord.Key, srvRecord.Host)
+		// SRV records are stored in the following form
+		// /skydns/net/miniocloud/bucket1, so this function serves multiple
+		// purposes basically when we do a Get(bucketName) this function
+		// should return a single DNS record for any input 'bucketName'.
+		//
+		// In all other situations when we want to list all DNS records,
+		// which is handled in the else clause.
+		if key != msg.Path(fmt.Sprintf(".%s.", c.domainName), defaultPrefixPath) {
+			if srvRecord.Key == "/" {
 				srvRecords = append(srvRecords, srvRecord)
+			}
+		} else {
+			srvRecords = append(srvRecords, srvRecord)
+		}
 
 	}
-	if srvRecords != nil {
+	if len(srvRecords) == 0 {
+		return nil, ErrNoEntriesFound
+	}
 	sort.Slice(srvRecords, func(i int, j int) bool {
 		return srvRecords[i].Key < srvRecords[j].Key
 	})
-	} else {
-		return nil, ErrNoEntriesFound
-	}
 	return srvRecords, nil
 }
 
@@ -123,9 +135,18 @@ func (c *coreDNS) Put(bucket string) error {
 // Removes DNS entries added in Put().
 func (c *coreDNS) Delete(bucket string) error {
 	key := msg.Path(fmt.Sprintf("%s.%s.", bucket, c.domainName), defaultPrefixPath)
-	ctx, cancel := context.WithTimeout(context.Background(), defaultContextTimeout)
-	_, err := c.etcdClient.Delete(ctx, key)
-	defer cancel()
+	srvRecords, err := c.list(key)
+	if err != nil {
+		return err
+	}
+	for _, record := range srvRecords {
+		dctx, dcancel := context.WithTimeout(context.Background(), defaultContextTimeout)
+		if _, err = c.etcdClient.Delete(dctx, key+"/"+record.Host); err != nil {
+			dcancel()
+			return err
+		}
+		dcancel()
+	}
 	return err
 }