Add support for human-friendly TTL values

Supports specifying TTL values in Golang duration format for
`external-dns.alpha.kubernetes.io/ttl` annotation.

docs/ttl.md

@@ -2,6 +2,7 @@ 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 configure it, simply annotate a service/ingress, e.g.:
 
@@ -15,7 +16,21 @@ metadata:
   ...
 ```
 
-TTL must be a positive integer encoded as string.
+TTL can also be specified as a duration value parsable by Golang [time.ParseDuration](https://golang.org/pkg/time/#ParseDuration):
+
+```yaml
+apiVersion: v1
+kind: Service
+metadata:
+  annotations:
+    external-dns.alpha.kubernetes.io/hostname: nginx.external-dns-test.my-org.com.
+    external-dns.alpha.kubernetes.io/ttl: "1m"
+  ...
+```
+
+Both examples result in the same value of 60 seconds TTL.
+
+TTL must be a positive value.
 
 Providers
 =========

source/gateway_test.go

@@ -936,6 +936,15 @@ func testGatewayEndpoints(t *testing.T) {
 					},
 					dnsnames: [][]string{{"example2.org"}},
 				},
+				{
+					name:      "fake3",
+					namespace: namespace,
+					annotations: map[string]string{
+						targetAnnotationKey: "gateway-target.com",
+						ttlAnnotationKey:    "10s",
+					},
+					dnsnames: [][]string{{"example3.org"}},
+				},
 			},
 			expected: []*endpoint.Endpoint{
 				{
@@ -948,6 +957,11 @@ func testGatewayEndpoints(t *testing.T) {
 					Targets:   endpoint.Targets{"gateway-target.com"},
 					RecordTTL: endpoint.TTL(1),
 				},
+				{
+					DNSName:   "example3.org",
+					Targets:   endpoint.Targets{"gateway-target.com"},
+					RecordTTL: endpoint.TTL(10),
+				},
 			},
 		},
 		{

source/ingress_test.go

@@ -816,6 +816,16 @@ func testIngressEndpoints(t *testing.T) {
 					dnsnames: []string{"example2.org"},
 					ips:      []string{"8.8.8.8"},
 				},
+				{
+					name:      "fake3",
+					namespace: namespace,
+					annotations: map[string]string{
+						targetAnnotationKey: "ingress-target.com",
+						ttlAnnotationKey:    "10s",
+					},
+					dnsnames: []string{"example3.org"},
+					ips:      []string{"8.8.4.4"},
+				},
 			},
 			expected: []*endpoint.Endpoint{
 				{
@@ -828,6 +838,11 @@ func testIngressEndpoints(t *testing.T) {
 					Targets:   endpoint.Targets{"ingress-target.com"},
 					RecordTTL: endpoint.TTL(1),
 				},
+				{
+					DNSName:   "example3.org",
+					Targets:   endpoint.Targets{"ingress-target.com"},
+					RecordTTL: endpoint.TTL(10),
+				},
 			},
 		},
 		{

source/ingressroute_test.go

@@ -824,6 +824,15 @@ func testIngressRouteEndpoints(t *testing.T) {
 					},
 					host: "example2.org",
 				},
+				{
+					name:      "fake3",
+					namespace: namespace,
+					annotations: map[string]string{
+						targetAnnotationKey: "ingressroute-target.com",
+						ttlAnnotationKey:    "10s",
+					},
+					host: "example3.org",
+				},
 			},
 			expected: []*endpoint.Endpoint{
 				{
@@ -836,6 +845,11 @@ func testIngressRouteEndpoints(t *testing.T) {
 					Targets:   endpoint.Targets{"ingressroute-target.com"},
 					RecordTTL: endpoint.TTL(1),
 				},
+				{
+					DNSName:   "example3.org",
+					Targets:   endpoint.Targets{"ingressroute-target.com"},
+					RecordTTL: endpoint.TTL(10),
+				},
 			},
 		},
 		{

source/service_test.go

@@ -971,6 +971,30 @@ func testServiceSourceEndpoints(t *testing.T) {
 			},
 			false,
 		},
+		{
+			"ttl annotated (in duration format) and is valid should set Record.TTL",
+			"",
+			"",
+			"testing",
+			"foo",
+			v1.ServiceTypeLoadBalancer,
+			"",
+			"",
+			false,
+			false,
+			map[string]string{},
+			map[string]string{
+				hostnameAnnotationKey: "foo.example.org.",
+				ttlAnnotationKey:      "1m",
+			},
+			"",
+			[]string{"1.2.3.4"},
+			[]string{},
+			[]*endpoint.Endpoint{
+				{DNSName: "foo.example.org", Targets: endpoint.Targets{"1.2.3.4"}, RecordTTL: endpoint.TTL(60)},
+			},
+			false,
+		},
 		{
 			"Negative ttl is not valid",
 			"",

source/source.go

@@ -22,6 +22,7 @@ import (
 	"net"
 	"strconv"
 	"strings"
+	"time"
 
 	"github.com/kubernetes-incubator/external-dns/endpoint"
 )
@@ -63,7 +64,7 @@ func getTTLFromAnnotations(annotations map[string]string) (endpoint.TTL, error)
 	if !exists {
 		return ttlNotConfigured, nil
 	}
-	ttlValue, err := strconv.ParseInt(ttlAnnotation, 10, 64)
+	ttlValue, err := parseTTL(ttlAnnotation)
 	if err != nil {
 		return ttlNotConfigured, fmt.Errorf("\"%v\" is not a valid TTL value", ttlAnnotation)
 	}
@@ -73,6 +74,21 @@ func getTTLFromAnnotations(annotations map[string]string) (endpoint.TTL, error)
 	return endpoint.TTL(ttlValue), nil
 }
 
+// parseTTL parses TTL from string, returning duration in seconds.
+// parseTTL supports both integers like "600" and durations based
+// on Go Duration like "10m", hence "600" and "10m" represent the same value.
+//
+// Note: for durations like "1.5s" the fraction is omitted (resulting in 1 second
+// for the example).
+func parseTTL(s string) (ttlSeconds int64, err error) {
+	ttlDuration, err := time.ParseDuration(s)
+	if err != nil {
+		return strconv.ParseInt(s, 10, 64)
+	}
+
+	return int64(ttlDuration.Seconds()), nil
+}
+
 func getHostnamesFromAnnotations(annotations map[string]string) []string {
 	hostnameAnnotation, exists := annotations[hostnameAnnotationKey]
 	if !exists {

source/source_test.go

@@ -62,11 +62,23 @@ func TestGetTTLFromAnnotations(t *testing.T) {
 			expectedErr: fmt.Errorf("TTL value must be between [%d, %d]", ttlMinimum, ttlMaximum),
 		},
 		{
-			title:       "TTL annotation value is set correctly",
+			title:       "TTL annotation value is set correctly using integer",
 			annotations: map[string]string{ttlAnnotationKey: "60"},
 			expectedTTL: endpoint.TTL(60),
 			expectedErr: nil,
 		},
+		{
+			title: "TTL annotation value is set correctly using duration (whole)",
+			annotations: map[string]string{ttlAnnotationKey: "10m"},
+			expectedTTL: endpoint.TTL(600),
+			expectedErr: nil,
+		},
+		{
+			title: "TTL annotation value is set correcly using duration (fractional)",
+			annotations: map[string]string{ttlAnnotationKey: "20.5s"},
+			expectedTTL: endpoint.TTL(20),
+			expectedErr: nil,
+		},
 	} {
 		t.Run(tc.title, func(t *testing.T) {
 			ttl, err := getTTLFromAnnotations(tc.annotations)