feat(txt-registry): add option to use only new format

docs/registry/txt.md

@@ -3,6 +3,24 @@
 The TXT registry is the default registry.
 It stores DNS record metadata in TXT records, using the same provider.
 
+## Record Format Options
+The TXT registry supports two formats for storing DNS record metadata:
+- Legacy format: Creates a TXT record without record type information
+- New format: Creates a TXT record with record type information (e.g., 'a-' prefix for A records)
+
+By default, the TXT registry creates records in both formats for backwards compatibility. You can configure it to use only the new format by using the `--txt-new-format-only` flag. This reduces the number of TXT records created, which can be helpful when working with provider-specific record limits.
+
+Note: AAAA records always use only the new format regardless of this setting.
+
+Example:
+```sh
+# Default behavior - creates both formats
+external-dns
+
+# Only create new format records
+external-dns --txt-new-format-only
+```
+
 ## Prefixes and Suffixes
 
 In order to avoid having the registry TXT records collide with

main.go

@@ -387,7 +387,7 @@ func main() {
 	case "noop":
 		r, err = registry.NewNoopRegistry(p)
 	case "txt":
-		r, err = registry.NewTXTRegistry(p, cfg.TXTPrefix, cfg.TXTSuffix, cfg.TXTOwnerID, cfg.TXTCacheInterval, cfg.TXTWildcardReplacement, cfg.ManagedDNSRecordTypes, cfg.ExcludeDNSRecordTypes, cfg.TXTEncryptEnabled, []byte(cfg.TXTEncryptAESKey))
+		r, err = registry.NewTXTRegistry(p, cfg.TXTPrefix, cfg.TXTSuffix, cfg.TXTOwnerID, cfg.TXTCacheInterval, cfg.TXTWildcardReplacement, cfg.ManagedDNSRecordTypes, cfg.ExcludeDNSRecordTypes, cfg.TXTEncryptEnabled, []byte(cfg.TXTEncryptAESKey), cfg.TXTNewFormatOnly)
 	case "aws-sd":
 		r, err = registry.NewAWSSDRegistry(p, cfg.TXTOwnerID)
 	default:

pkg/apis/externaldns/types.go

@@ -138,6 +138,7 @@ type Config struct {
 	TXTSuffix                          string
 	TXTEncryptEnabled                  bool
 	TXTEncryptAESKey                   string `secure:"yes"`
+	TXTNewFormatOnly                   bool
 	Interval                           time.Duration
 	MinEventSyncInterval               time.Duration
 	Once                               bool
@@ -299,6 +300,7 @@ var defaultConfig = &Config{
 	MinEventSyncInterval:        5 * time.Second,
 	TXTEncryptEnabled:           false,
 	TXTEncryptAESKey:            "",
+	TXTNewFormatOnly:            false,
 	Interval:                    time.Minute,
 	Once:                        false,
 	DryRun:                      false,
@@ -580,6 +582,7 @@ func (cfg *Config) ParseFlags(args []string) error {
 	app.Flag("txt-wildcard-replacement", "When using the TXT registry, a custom string that's used instead of an asterisk for TXT records corresponding to wildcard DNS records (optional)").Default(defaultConfig.TXTWildcardReplacement).StringVar(&cfg.TXTWildcardReplacement)
 	app.Flag("txt-encrypt-enabled", "When using the TXT registry, set if TXT records should be encrypted before stored (default: disabled)").BoolVar(&cfg.TXTEncryptEnabled)
 	app.Flag("txt-encrypt-aes-key", "When using the TXT registry, set TXT record decryption and encryption 32 byte aes key (required when --txt-encrypt=true)").Default(defaultConfig.TXTEncryptAESKey).StringVar(&cfg.TXTEncryptAESKey)
+	app.Flag("txt-new-format-only", "When using the TXT registry, only use new format records which include record type information (e.g., prefix: 'a-'). Reduces number of TXT records (default: disabled)").Default(defaultConfig.TXTNewFormatOnly).BoolVar(&cfg.TXTNewFormatOnly)
 	app.Flag("dynamodb-region", "When using the DynamoDB registry, the AWS region of the DynamoDB table (optional)").Default(cfg.AWSDynamoDBRegion).StringVar(&cfg.AWSDynamoDBRegion)
 	app.Flag("dynamodb-table", "When using the DynamoDB registry, the name of the DynamoDB table (default: \"external-dns\")").Default(defaultConfig.AWSDynamoDBTable).StringVar(&cfg.AWSDynamoDBTable)
 

registry/txt.go

@@ -56,10 +56,19 @@ type TXTRegistry struct {
 	// encrypt text records
 	txtEncryptEnabled bool
 	txtEncryptAESKey  []byte
+
+	newFormatOnly bool
 }
 
-// NewTXTRegistry returns new TXTRegistry object
-func NewTXTRegistry(provider provider.Provider, txtPrefix, txtSuffix, ownerID string, cacheInterval time.Duration, txtWildcardReplacement string, managedRecordTypes, excludeRecordTypes []string, txtEncryptEnabled bool, txtEncryptAESKey []byte) (*TXTRegistry, error) {
+// NewTXTRegistry returns a new TXTRegistry object. When newFormatOnly is true, it will only
+// generate new format TXT records, otherwise it generates both old and new formats for
+// backwards compatibility.
+func NewTXTRegistry(provider provider.Provider, txtPrefix, txtSuffix, ownerID string,
+	cacheInterval time.Duration, txtWildcardReplacement string,
+	managedRecordTypes, excludeRecordTypes []string,
+	txtEncryptEnabled bool, txtEncryptAESKey []byte,
+	newFormatOnly bool) (*TXTRegistry, error) {
+
 	if ownerID == "" {
 		return nil, errors.New("owner id cannot be empty")
 	}
@@ -88,6 +97,7 @@ func NewTXTRegistry(provider provider.Provider, txtPrefix, txtSuffix, ownerID st
 		excludeRecordTypes:  excludeRecordTypes,
 		txtEncryptEnabled:   txtEncryptEnabled,
 		txtEncryptAESKey:    txtEncryptAESKey,
+		newFormatOnly:       newFormatOnly,
 	}, nil
 }
 
@@ -209,12 +219,14 @@ func (im *TXTRegistry) Records(ctx context.Context) ([]*endpoint.Endpoint, error
 	return endpoints, nil
 }
 
-// generateTXTRecord generates both "old" and "new" TXT records.
-// Once we decide to drop old format we need to drop toTXTName() and rename toNewTXTName
+// generateTXTRecord generates TXT records in either both formats (old and new) or new format only,
+// depending on the newFormatOnly configuration. The old format is maintained for backwards
+// compatibility but can be disabled to reduce the number of DNS records.
 func (im *TXTRegistry) generateTXTRecord(r *endpoint.Endpoint) []*endpoint.Endpoint {
 	endpoints := make([]*endpoint.Endpoint, 0)
 
-	if !im.txtEncryptEnabled && !im.mapper.recordTypeInAffix() && r.RecordType != endpoint.RecordTypeAAAA {
+	// Create legacy format record by default unless newFormatOnly is true
+	if !im.newFormatOnly && !im.txtEncryptEnabled && !im.mapper.recordTypeInAffix() && r.RecordType != endpoint.RecordTypeAAAA {
 		// old TXT record format
 		txt := endpoint.NewEndpoint(im.mapper.toTXTName(r.DNSName), endpoint.RecordTypeTXT, r.Labels.Serialize(true, im.txtEncryptEnabled, im.txtEncryptAESKey))
 		if txt != nil {
@@ -224,7 +236,8 @@ func (im *TXTRegistry) generateTXTRecord(r *endpoint.Endpoint) []*endpoint.Endpo
 			endpoints = append(endpoints, txt)
 		}
 	}
-	// new TXT record format (containing record type)
+
+	// Always create new format record
 	recordType := r.RecordType
 	// AWS Alias records are encoded as type "cname"
 	if isAlias, found := r.GetProviderSpecificProperty("alias"); found && isAlias == "true" && recordType == endpoint.RecordTypeA {