Do not block NotFound error during patching resources (#2403)

storage-version-migration-serving crashes if ksvc deleted during
migration.

Please refer to the following error especially
`services.serving.knative.dev \"receiver261\" not found` message.

```
{"severity":"INFO","timestamp":"2022-01-25T14:17:19.840090884Z","caller":"logging/config.go:116","message":"Successfully created the logger."}
{"severity":"INFO","timestamp":"2022-01-25T14:17:19.840350704Z","caller":"logging/config.go:117","message":"Logging level set to: info"}
{"severity":"INFO","timestamp":"2022-01-25T14:17:19.840399959Z","caller":"logging/config.go:79","message":"Fetch GitHub commit ID from kodata failed","error":"\"KO_DATA_PATH\" does not exist or is empty"}
{"severity":"INFO","timestamp":"2022-01-25T14:17:19.854296148Z","logger":"storage-migrator","caller":"migrate/main.go:60","message":"Migrating 4 group resources"}
{"severity":"INFO","timestamp":"2022-01-25T14:17:19.85439718Z","logger":"storage-migrator","caller":"migrate/main.go:63","message":"Migrating group resource services.serving.knative.dev"}
{"severity":"EMERGENCY","timestamp":"2022-01-25T14:17:47.601002153Z","logger":"storage-migrator","caller":"migrate/main.go:65","message":"Failed to migrate: unable to patch resource kc-broker-newsubs-kn-0/receiver261 (gvr: serving.knative.dev/v1, Resource=services) - services.serving.knative.dev \"receiver261\" not found","stacktrace":"main.main\n\t/opt/app-root/src/go/src/knative.dev/serving/vendor/knative.dev/pkg/apiextensions/storageversion/cmd/migrate/main.go:65\nruntime.main\n\t/usr/lib/golang/src/runtime/proc.go:255"}
```

It could be a rare case but it happens when an user delete their
resource during storage-version-migration-serving is running.

This patch fixes the issue by ignoring the NotFound error during
patching resources.

apiextensions/storageversion/migrator.go

@@ -22,6 +22,7 @@ import (
 
 	apix "k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1"
 	apixclient "k8s.io/apiextensions-apiserver/pkg/client/clientset/clientset"
+	apierrs "k8s.io/apimachinery/pkg/api/errors"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/runtime/schema"
@@ -93,7 +94,7 @@ func (m *Migrator) migrateResources(ctx context.Context, gvr schema.GroupVersion
 		_, err := client.Namespace(item.GetNamespace()).
 			Patch(ctx, item.GetName(), types.MergePatchType, []byte("{}"), metav1.PatchOptions{})
 
-		if err != nil {
+		if err != nil && !apierrs.IsNotFound(err) {
 			return fmt.Errorf("unable to patch resource %s/%s (gvr: %s) - %w",
 				item.GetNamespace(), item.GetName(),
 				gvr, err)

apiextensions/storageversion/migrator_test.go

@@ -24,6 +24,7 @@ import (
 	"github.com/google/go-cmp/cmp"
 	apix "k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1"
 	apixFake "k8s.io/apiextensions-apiserver/pkg/client/clientset/clientset/fake"
+	apierrs "k8s.io/apimachinery/pkg/api/errors"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 	runtime "k8s.io/apimachinery/pkg/runtime"
@@ -97,6 +98,7 @@ func TestMigrate_Errors(t *testing.T) {
 		name string
 		crd  func(*k8stesting.Fake)
 		dyn  func(*k8stesting.Fake)
+		pass bool
 	}{{
 		name: "failed to fetch CRD",
 		crd: func(fake *k8stesting.Fake) {
@@ -129,6 +131,16 @@ func TestMigrate_Errors(t *testing.T) {
 					return true, nil, errors.New("failed to patch definition")
 				})
 		},
+	}, {
+		name: "patching unexisting resource",
+		dyn: func(fake *k8stesting.Fake) {
+			fake.PrependReactor("patch", "*",
+				func(k8stesting.Action) (bool, runtime.Object, error) {
+					return true, nil, apierrs.NewNotFound(fakeGR, "resource-removed")
+				})
+		},
+		// Resouce not found error should not block the storage migration.
+		pass: true,
 	},
 	// todo paging fails
 	}
@@ -148,7 +160,7 @@ func TestMigrate_Errors(t *testing.T) {
 			}
 
 			m := NewMigrator(dclient, cclient)
-			if err := m.Migrate(context.Background(), fakeGR); err == nil {
+			if err := m.Migrate(context.Background(), fakeGR); test.pass != (err == nil) {
 				t.Error("Migrate should have returned an error")
 			}
 		})