[v1.8.x] fix(helm-operator): do not send empty patch requests to kube apiserver (#4971)

Adding a check to filter out empty patch requests from an empty map
out of the 3-way merge.
    
Signed-off-by: Cheuk Lam <[email protected]>
Co-authored-by: Eric Stroczynski <[email protected]>

Author: openshift-cherrypick-robot

changelog/fragments/empty-patch-requests.yaml

@@ -0,0 +1,4 @@
+entries:
+  - description: >
+      For helm-based operators, empty patch requests generated from the 3-way merge are filtered to avoid unnecessary requests to the kube apiserver.
+    kind: bugfix

internal/helm/release/manager.go

@@ -322,7 +322,15 @@ func createPatch(existing runtime.Object, expected *resource.Info) ([]byte, apit
 	}
 
 	patch, err := strategicpatch.CreateThreeWayMergePatch(expectedJSON, expectedJSON, existingJSON, patchMeta, true)
-	return patch, apitypes.StrategicMergePatchType, err
+	if err != nil {
+		return nil, apitypes.StrategicMergePatchType, err
+	}
+	// An empty patch could be in the form of "{}" which represents an empty map out of the 3-way merge;
+	// filter them out here too to avoid sending the apiserver empty patch requests.
+	if len(patch) == 0 || bytes.Equal(patch, []byte("{}")) {
+		return nil, apitypes.StrategicMergePatchType, nil
+	}
+	return patch, apitypes.StrategicMergePatchType, nil
 }
 
 func createJSONMergePatch(existingJSON, expectedJSON []byte) ([]byte, error) {

internal/helm/release/manager_test.go

@@ -164,7 +164,7 @@ func TestManagerGenerateStrategicMergePatch(t *testing.T) {
 			o2: newTestDeployment([]v1.Container{
 				{Name: "test1", LivenessProbe: nil},
 			}),
-			patch:     `{}`,
+			patch:     ``,
 			patchType: apitypes.StrategicMergePatchType,
 		},
 		{
@@ -197,7 +197,7 @@ func TestManagerGenerateStrategicMergePatch(t *testing.T) {
 				},
 				Spec: appsv1.DeploymentSpec{},
 			},
-			patch:     `{}`,
+			patch:     ``,
 			patchType: apitypes.StrategicMergePatchType,
 		},
 	}