fix: use cached v1.15-azs kube-proxy on Azure Stack (#3757)

Author: jadarsie

Diff for: pkg/api/addons.go

@@ -771,7 +771,7 @@ func (cs *ContainerService) setAddonsConfig(isUpgrade bool) {
 		Containers: []KubernetesContainerSpec{
 			{
 				Name:  common.KubeProxyAddonName,
-				Image: kubernetesImageBase + k8sComponents[common.KubeProxyAddonName],
+				Image: kubernetesImageBase + k8sComponents[common.KubeProxyAddonName] + kubeProxyImageSuffix(*cs),
 			},
 		},
 	}
@@ -1203,3 +1203,15 @@ func getCSISidecarComponent(csiDriverName, csiSidecarName string, k8sComponents
 	}
 	return k8sComponents[csiSidecarName]
 }
+
+// kubeProxyImageSuffix returns '-azs' if target cloud is Azure Stack and Kubernetes version is lower than v1.16.0.
+// Otherwise, it returns empty string.
+// Azure Stack needs the '-azs' suffix so kube-proxy's manifests uses the custom hyperkube image present in the VHD
+func kubeProxyImageSuffix(cs ContainerService) string {
+	if cs.Properties.IsAzureStackCloud() {
+		if !common.IsKubernetesVersionGe(cs.Properties.OrchestratorProfile.OrchestratorVersion, "1.16.0") {
+			return common.AzureStackSuffix
+		}
+	}
+	return ""
+}

Diff for: pkg/api/addons_test.go

@@ -6,6 +6,7 @@ package api
 import (
 	"reflect"
 	"strconv"
+	"strings"
 	"testing"
 
 	"github.com/Azure/aks-engine/pkg/api/common"
@@ -2157,7 +2158,7 @@ func TestSetAddonsConfig(t *testing.T) {
 					Containers: []KubernetesContainerSpec{
 						{
 							Name:  common.KubeProxyAddonName,
-							Image: "MCRKubernetesImageBase" + k8sComponentsByVersionMap["1.15.12"][common.KubeProxyAddonName],
+							Image: "MCRKubernetesImageBase" + k8sComponentsByVersionMap["1.15.12"][common.KubeProxyAddonName] + common.AzureStackSuffix,
 						},
 					},
 				},
@@ -5375,3 +5376,50 @@ func TestGetCSISidecarComponent(t *testing.T) {
 		})
 	}
 }
+
+func TestKubeProxyImageSuffix(t *testing.T) {
+	cases := []struct {
+		name       string
+		cs         ContainerService
+		azurestack bool
+		expected   string
+	}{
+		{
+			name:       "return empty string if target cloud is NOT Azure Stack",
+			cs:         getMockBaseContainerService("1.15.0"),
+			azurestack: false,
+			expected:   "",
+		},
+		{
+			name:       "return empty string if target cloud is NOT Azure Stack",
+			cs:         getMockBaseContainerService("1.16.0"),
+			azurestack: false,
+			expected:   "",
+		},
+		{
+			name:       "return empty string if target version is v1.16 or greater",
+			cs:         getMockBaseContainerService("1.16.0"),
+			azurestack: true,
+			expected:   "",
+		},
+		{
+			name:       "return '-azs' if target cloud is Azure Stack and K8s version lower than v1.16",
+			cs:         getMockBaseContainerService("1.15.0"),
+			azurestack: true,
+			expected:   common.AzureStackSuffix,
+		},
+	}
+	for _, tc := range cases {
+		c := tc
+		t.Run(c.name, func(t *testing.T) {
+			t.Parallel()
+			if c.azurestack {
+				c.cs.Properties.CustomCloudProfile = &CustomCloudProfile{}
+			}
+			actual := kubeProxyImageSuffix(c.cs)
+			if !strings.EqualFold(actual, c.expected) {
+				t.Errorf("expected %s to be %s", actual, c.expected)
+			}
+		})
+	}
+}