Fixes prefixed annotations support.

provider/kubernetes/annotations.go

@@ -77,13 +77,13 @@ func getAnnotationName(annotations map[string]string, name string) string {
 	}
 
 	if _, ok := annotations[label.Prefix+name]; ok {
-		return name
+		return label.Prefix + name
 	}
 
 	// TODO [breaking] remove label support
 	if lbl, compat := compatibilityMapping[name]; compat {
 		if _, ok := annotations[lbl]; ok {
-			return name
+			return lbl
 		}
 	}
 

provider/kubernetes/annotations_test.go

@@ -0,0 +1,52 @@
+package kubernetes
+
+import (
+	"testing"
+
+	"github.com/containous/traefik/provider/label"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestGetAnnotationName(t *testing.T) {
+	testCases := []struct {
+		desc        string
+		annotations map[string]string
+		name        string
+		expected    string
+	}{
+		{
+			desc: "with standard annotation",
+			name: annotationKubernetesPreserveHost,
+			annotations: map[string]string{
+				annotationKubernetesPreserveHost: "true",
+			},
+			expected: annotationKubernetesPreserveHost,
+		},
+		{
+			desc: "with prefixed annotation",
+			name: annotationKubernetesPreserveHost,
+			annotations: map[string]string{
+				label.Prefix + annotationKubernetesPreserveHost: "true",
+			},
+			expected: label.Prefix + annotationKubernetesPreserveHost,
+		},
+		{
+			desc: "with label",
+			name: annotationKubernetesPreserveHost,
+			annotations: map[string]string{
+				label.TraefikFrontendPassHostHeader: "true",
+			},
+			expected: label.TraefikFrontendPassHostHeader,
+		},
+	}
+
+	for _, test := range testCases {
+		test := test
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			actual := getAnnotationName(test.annotations, test.name)
+			assert.Equal(t, test.expected, actual)
+		})
+	}
+}