feat(source): add min-ttl support

controller/execute.go

@@ -456,6 +456,7 @@ func buildSource(ctx context.Context, cfg *externaldns.Config) (source.Source, e
 		combinedSource = wrappers.NewTargetFilterSource(combinedSource, targetFilter)
 		cfg.AddSourceWrapper("target-filter")
 	}
+	combinedSource = wrappers.NewPostProcessor(combinedSource, wrappers.WithTTL(cfg.MinTTL))
 	return combinedSource, nil
 }
 

docs/advanced/ttl.md

@@ -1,9 +1,15 @@
 # Configure DNS record TTL (Time-To-Live)
 
-An optional annotation `external-dns.alpha.kubernetes.io/ttl` is available to customize the TTL value of a DNS record.
-TTL is specified as an integer encoded as string representing seconds.
+> To customize DNS record TTL (Time-To-Live) in a DNS record`, you can use the `external-dns.alpha.kubernetes.io/ttl: <duration>` annotation or flag `--min-ttl=<duration>`. TTL is specified as an integer encoded as string representing seconds. Example; `1s`, `1m2s`, `1h2m11s`
 
-To configure it, simply annotate a service/ingress, e.g.:
+Behaviour:
+
+- If the `external-dns.alpha.kubernetes.io/ttl` annotation is set, it overrides the default TTL(0) value.
+- If the annotation is not set, the default TTL value is used, unless the `--min-ttl` flag is provided.
+- If the annotation is set to `0`, and the `--min-ttl=1s` flag is provided, the value from `--min-ttl` will be used instead.
+- Not all providers support the custom TTL value, and some may override it with their own default values.
+
+To configure it, annotate a service/ingress, e.g.:
 
 ```yaml
 apiVersion: v1
@@ -140,7 +146,7 @@ The Linode Provider default TTL is used when the TTL is 0. The default is 24 hou
 
 The TransIP Provider minimal TTL is used when the TTL is 0. The minimal TTL is 60s.
 
-## Use Cases for `external-dns.alpha.kubernetes.io/ttl` annotation
+## Use Cases for `external-dns.alpha.kubernetes.io/ttl` annotation and `--min-ttl` flag`
 
 The `external-dns.alpha.kubernetes.io/ttl` annotation allows you to set a custom **TTL (Time To Live)** for DNS records managed by `external-dns`.
 

docs/annotations/annotations.md

@@ -175,7 +175,9 @@ are published as CNAME records.
 Specifies the TTL (time to live) for the resource's DNS records.
 
 The value may be specified as either a duration or an integer number of seconds.
-It must be between 1 and 2,147,483,647 seconds.
+It must be between `1` and `2,147,483,647` seconds.
+
+> Note; setting the value to `0` means, that TTL is not configured and thus use default.
 
 ## Provider-specific annotations
 

docs/contributing/source-wrappers.md

@@ -31,6 +31,7 @@ Wrappers solve these key challenges:
 |    `DedupSource`     | Remove duplicate DNS records.           | Avoid duplicate records from sources. |
 | `TargetFilterSource` | Include/exclude targets based on CIDRs. | Exclude internal IPs.                 |
 |    `NAT64Source`     | Add NAT64-prefixed AAAA records.        | Support IPv6 with NAT64.              |
+|   `PostProcessor`    | Add records post-processing.            | Configure TTL for all endpoints.      |
 
 ### Use Cases
 

docs/flags.md

@@ -174,6 +174,7 @@
 | `--[no-]once` | When enabled, exits the synchronization loop after the first iteration (default: disabled) |
 | `--[no-]dry-run` | When enabled, prints DNS record changes rather than actually performing them (default: disabled) |
 | `--[no-]events` | When enabled, in addition to running every interval, the reconciliation loop will get triggered when supported sources change (default: disabled) |
+| `--min-ttl=MIN-TTL` | Configure global TTL for records in duration format. This value is used when the TTL for a source is not set or set to 0. (optional; examples: 1m12s, 72s, 72) |
 | `--log-format=text` | The format in which log messages are printed (default: text, options: text, json) |
 | `--metrics-address=":7979"` | Specify where to serve the metrics and health check endpoint (default: :7979) |
 | `--log-level=info` | Set the level of logging. (default: info, options: panic, debug, info, warning, error, fatal) |

endpoint/endpoint.go

@@ -420,6 +420,14 @@ func (e *Endpoint) CheckEndpoint() bool {
 	return true
 }
 
+// WithMinTTL sets the endpoint's TTL to the given value if the current TTL is not configured.
+func (e *Endpoint) WithMinTTL(ttl int64) {
+	if !e.RecordTTL.IsConfigured() && ttl > 0 {
+		log.Debugf("Overriding existing TTL %d with new value %d for endpoint %s", e.RecordTTL, ttl, e.DNSName)
+		e.RecordTTL = TTL(ttl)
+	}
+}
+
 // NewMXRecord parses a string representation of an MX record target (e.g., "10 mail.example.com")
 // and returns an MXTarget struct. Returns an error if the input is invalid.
 func NewMXRecord(target string) (*MXTarget, error) {

endpoint/endpoint_test.go

@@ -989,3 +989,50 @@ func TestTargets_UniqueOrdered(t *testing.T) {
 		})
 	}
 }
+
+func TestEndpoint_WithMinTTL(t *testing.T) {
+	tests := []struct {
+		name         string
+		initialTTL   TTL
+		inputTTL     int64
+		expectedTTL  TTL
+		isConfigured bool
+	}{
+		{
+			name:         "sets TTL when not configured and input > 0",
+			initialTTL:   0,
+			inputTTL:     300,
+			expectedTTL:  300,
+			isConfigured: true,
+		},
+		{
+			name:         "does not override when already configured",
+			initialTTL:   120,
+			inputTTL:     300,
+			expectedTTL:  120,
+			isConfigured: true,
+		},
+		{
+			name:         "does not set when input is zero",
+			initialTTL:   30,
+			inputTTL:     0,
+			expectedTTL:  30,
+			isConfigured: true,
+		},
+		{
+			name:        "does not set when input is negative",
+			initialTTL:  0,
+			inputTTL:    -10,
+			expectedTTL: 0,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			ep := &Endpoint{RecordTTL: tt.initialTTL}
+			ep.WithMinTTL(tt.inputTTL)
+			assert.Equal(t, tt.expectedTTL, ep.RecordTTL)
+			assert.Equal(t, tt.isConfigured, ep.RecordTTL.IsConfigured())
+		})
+	}
+}

pkg/apis/externaldns/types.go

@@ -147,6 +147,7 @@ type Config struct {
 	TXTEncryptAESKey                              string `secure:"yes"`
 	Interval                                      time.Duration
 	MinEventSyncInterval                          time.Duration
+	MinTTL                                        time.Duration
 	Once                                          bool
 	DryRun                                        bool
 	UpdateEvents                                  bool
@@ -654,6 +655,7 @@ func App(cfg *Config) *kingpin.Application {
 	app.Flag("once", "When enabled, exits the synchronization loop after the first iteration (default: disabled)").BoolVar(&cfg.Once)
 	app.Flag("dry-run", "When enabled, prints DNS record changes rather than actually performing them (default: disabled)").BoolVar(&cfg.DryRun)
 	app.Flag("events", "When enabled, in addition to running every interval, the reconciliation loop will get triggered when supported sources change (default: disabled)").BoolVar(&cfg.UpdateEvents)
+	app.Flag("min-ttl", "Configure global TTL for records in duration format. This value is used when the TTL for a source is not set or set to 0. (optional; examples: 1m12s, 72s, 72)").DurationVar(&cfg.MinTTL)
 
 	// Miscellaneous flags
 	app.Flag("log-format", "The format in which log messages are printed (default: text, options: text, json)").Default(defaultConfig.LogFormat).EnumVar(&cfg.LogFormat, "text", "json")

source/wrappers/post_processor.go

@@ -0,0 +1,82 @@
+/*
+Copyright 2025 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package wrappers
+
+import (
+	"context"
+	"time"
+
+	log "github.com/sirupsen/logrus"
+
+	"sigs.k8s.io/external-dns/endpoint"
+	"sigs.k8s.io/external-dns/source"
+)
+
+type postProcessor struct {
+	source source.Source
+	cfg    PostProcessorConfig
+}
+
+type PostProcessorConfig struct {
+	ttl          int64
+	isConfigured bool
+}
+
+type PostProcessorOption func(*PostProcessorConfig)
+
+func WithTTL(ttl time.Duration) PostProcessorOption {
+	return func(cfg *PostProcessorConfig) {
+		if int64(ttl.Seconds()) > 0 {
+			cfg.isConfigured = true
+			cfg.ttl = int64(ttl.Seconds())
+		}
+	}
+}
+
+func NewPostProcessor(source source.Source, opts ...PostProcessorOption) source.Source {
+	cfg := PostProcessorConfig{}
+	for _, opt := range opts {
+		opt(&cfg)
+	}
+	return &postProcessor{source: source, cfg: cfg}
+}
+
+func (pp *postProcessor) Endpoints(ctx context.Context) ([]*endpoint.Endpoint, error) {
+	endpoints, err := pp.source.Endpoints(ctx)
+	if err != nil {
+		return nil, err
+	}
+
+	if !pp.cfg.isConfigured {
+		return endpoints, nil
+	}
+
+	for _, ep := range endpoints {
+		if ep == nil {
+			continue
+		}
+		ep.WithMinTTL(pp.cfg.ttl)
+		// Additional post-processing can be added here.
+	}
+
+	return endpoints, nil
+}
+
+func (pp *postProcessor) AddEventHandler(ctx context.Context, handler func()) {
+	log.Debug("postProcessor: adding event handler")
+	pp.source.AddEventHandler(ctx, handler)
+}