validation: allow trailing period in dns search

pkg/apis/core/validation/validation.go

@@ -2695,6 +2695,10 @@ func validatePodDNSConfig(dnsConfig *core.PodDNSConfig, dnsPolicy *core.DNSPolic
 			allErrs = append(allErrs, field.Invalid(fldPath.Child("searches"), dnsConfig.Searches, "must not have more than 256 characters (including spaces) in the search list"))
 		}
 		for i, search := range dnsConfig.Searches {
+			// it is fine to have a trailing dot
+			if strings.HasSuffix(search, ".") {
+				search = search[0 : len(search)-1]
+			}
 			allErrs = append(allErrs, ValidateDNS1123Subdomain(search, fldPath.Child("searches").Index(i))...)
 		}
 		// Validate options.

pkg/apis/core/validation/validation_test.go

@@ -5874,10 +5874,17 @@ func TestValidatePodDNSConfig(t *testing.T) {
 			expectedError: false,
 		},
 		{
+			desc: "valid: 1 search path with trailing period",
+			dnsConfig: &core.PodDNSConfig{
+				Searches: []string{"custom."},
+			},
+			expectedError: false,
+		},
+		{
 			desc: "valid: 3 nameservers and 6 search paths",
 			dnsConfig: &core.PodDNSConfig{
 				Nameservers: []string{"127.0.0.1", "10.0.0.10", "8.8.8.8"},
-				Searches:    []string{"custom", "mydomain.com", "local", "cluster.local", "svc.cluster.local", "default.svc.cluster.local"},
+				Searches:    []string{"custom", "mydomain.com", "local", "cluster.local", "svc.cluster.local", "default.svc.cluster.local."},
 			},
 			expectedError: false,
 		},