Set k8s default container label

pkg/reconciler/revision/resources/deploy.go

@@ -375,6 +375,7 @@ func MakeDeployment(rev *v1.Revision, cfg *config.Config) (*appsv1.Deployment, e
 
 	labels := makeLabels(rev)
 	anns := makeAnnotations(rev)
+	annsPod := makeAnnotationsForPod(rev, anns)
 
 	// Slowly but steadily roll the deployment out, to have the least possible impact.
 	maxUnavailable := intstr.FromInt(0)
@@ -399,7 +400,7 @@ func MakeDeployment(rev *v1.Revision, cfg *config.Config) (*appsv1.Deployment, e
 			Template: corev1.PodTemplateSpec{
 				ObjectMeta: metav1.ObjectMeta{
 					Labels:      labels,
-					Annotations: anns,
+					Annotations: annsPod,
 				},
 				Spec: *podSpec,
 			},

pkg/reconciler/revision/resources/deploy_test.go

@@ -272,7 +272,9 @@ var (
 						serving.RevisionUID:      "1234",
 						AppLabelKey:              "bar",
 					},
-					Annotations: map[string]string{},
+					Annotations: map[string]string{
+						DefaultContainerAnnotationName: servingContainerName,
+					},
 				},
 				// Spec: filled in by makePodSpec
 			},
@@ -1829,8 +1831,13 @@ func TestMakeDeployment(t *testing.T) {
 			}}), withoutLabels),
 		want: appsv1deployment(func(deploy *appsv1.Deployment) {
 			deploy.Spec.ProgressDeadlineSeconds = ptr.Int32(42)
-			deploy.Annotations = map[string]string{serving.ProgressDeadlineAnnotationKey: "42s"}
-			deploy.Spec.Template.Annotations = map[string]string{serving.ProgressDeadlineAnnotationKey: "42s"}
+			deploy.Annotations = map[string]string{
+				serving.ProgressDeadlineAnnotationKey: "42s",
+			}
+			deploy.Spec.Template.Annotations = map[string]string{
+				DefaultContainerAnnotationName:        servingContainerName,
+				serving.ProgressDeadlineAnnotationKey: "42s",
+			}
 		}),
 	}, {
 		name: "with ProgressDeadline annotation and configmap override",
@@ -1849,8 +1856,13 @@ func TestMakeDeployment(t *testing.T) {
 			}}), withoutLabels),
 		want: appsv1deployment(func(deploy *appsv1.Deployment) {
 			deploy.Spec.ProgressDeadlineSeconds = ptr.Int32(42)
-			deploy.Annotations = map[string]string{serving.ProgressDeadlineAnnotationKey: "42s"}
-			deploy.Spec.Template.Annotations = map[string]string{serving.ProgressDeadlineAnnotationKey: "42s"}
+			deploy.Annotations = map[string]string{
+				serving.ProgressDeadlineAnnotationKey: "42s",
+			}
+			deploy.Spec.Template.Annotations = map[string]string{
+				DefaultContainerAnnotationName:        servingContainerName,
+				serving.ProgressDeadlineAnnotationKey: "42s",
+			}
 		}),
 	}, {
 		name: "cluster initial scale",
@@ -1886,8 +1898,13 @@ func TestMakeDeployment(t *testing.T) {
 		),
 		want: appsv1deployment(func(deploy *appsv1.Deployment) {
 			deploy.Spec.Replicas = ptr.Int32(int32(20))
-			deploy.Spec.Template.Annotations = map[string]string{autoscaling.InitialScaleAnnotationKey: "20"}
-			deploy.Annotations = map[string]string{autoscaling.InitialScaleAnnotationKey: "20"}
+			deploy.Annotations = map[string]string{
+				autoscaling.InitialScaleAnnotationKey: "20",
+			}
+			deploy.Spec.Template.Annotations = map[string]string{
+				autoscaling.InitialScaleAnnotationKey: "20",
+				DefaultContainerAnnotationName:        servingContainerName,
+			}
 		}),
 	}}
 

pkg/reconciler/revision/resources/meta.go

@@ -17,6 +17,8 @@ limitations under the License.
 package resources
 
 import (
+	"maps"
+
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/util/sets"
 	"knative.dev/pkg/kmeta"
@@ -38,6 +40,10 @@ var (
 	)
 )
 
+const (
+	DefaultContainerAnnotationName = "kubectl.kubernetes.io/default-container"
+)
+
 // makeLabels constructs the labels we will apply to K8s resources.
 func makeLabels(revision *v1.Revision) map[string]string {
 	labels := kmeta.FilterMap(revision.GetLabels(), excludeLabels.Has)
@@ -59,6 +65,17 @@ func makeAnnotations(revision *v1.Revision) map[string]string {
 	return kmeta.FilterMap(revision.GetAnnotations(), excludeAnnotations.Has)
 }
 
+func makeAnnotationsForPod(revision *v1.Revision, baseAnnotations map[string]string) map[string]string {
+	podAnnotations := maps.Clone(baseAnnotations)
+
+	// Add default container annotation to the pod meta
+	if userContainer := revision.Spec.GetContainer(); userContainer.Name != "" {
+		podAnnotations[DefaultContainerAnnotationName] = userContainer.Name
+	}
+
+	return podAnnotations
+}
+
 // makeSelector constructs the Selector we will apply to K8s resources.
 func makeSelector(revision *v1.Revision) *metav1.LabelSelector {
 	return &metav1.LabelSelector{

pkg/reconciler/revision/resources/meta_test.go

@@ -20,6 +20,7 @@ import (
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
+	corev1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 
 	"knative.dev/serving/pkg/apis/serving"
@@ -141,3 +142,51 @@ func TestMakeAnnotations(t *testing.T) {
 		})
 	}
 }
+
+func TestMakeAnnotationsForPod(t *testing.T) {
+	tests := []struct {
+		name            string
+		rev             *v1.Revision
+		want            map[string]string
+		baseAnnotations map[string]string
+	}{{
+		name: "no container",
+		rev: &v1.Revision{
+			Spec: v1.RevisionSpec{
+				PodSpec: corev1.PodSpec{},
+			},
+		},
+		baseAnnotations: map[string]string{},
+		want:            map[string]string{},
+	}, {
+		name: "multiple containers single port with base annotation",
+		rev: &v1.Revision{
+			Spec: v1.RevisionSpec{
+				PodSpec: corev1.PodSpec{
+					Containers: []corev1.Container{{
+						Name: "foo",
+					}, {
+						Name: "bar",
+						Ports: []corev1.ContainerPort{{
+							ContainerPort: 8080,
+						}},
+					}},
+				},
+			},
+		},
+		baseAnnotations: map[string]string{"asdf": "fdsa"},
+		want: map[string]string{
+			"asdf":                         "fdsa",
+			DefaultContainerAnnotationName: "bar",
+		},
+	}}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			got := makeAnnotationsForPod(test.rev, test.baseAnnotations)
+			if diff := cmp.Diff(test.want, got); diff != "" {
+				t.Error("getUserContainerName (-want, +got) =", diff)
+			}
+		})
+	}
+}