Build workloads do not own custom kpack builders via ControllerReference

Custom kpack builders (the ones that are created on the fly for build
workloads with buildpacks specified) are shared by build workloads
that have the same set of buildpacks. Therefore, setting
ControllerReference from the build workload to the builder is incorrect
as the ControllerReference can only be set once.

Issue: #2645

kpack-image-builder/controllers/buildworkload_controller.go

@@ -466,7 +466,7 @@ func (r *BuildWorkloadReconciler) ensureKpackBuilder(ctx context.Context, log lo
 		},
 	}
 	_, err = ctrl.CreateOrUpdate(ctx, r.k8sClient, builder, func() error {
-		if err = controllerutil.SetControllerReference(buildWorkload, builder, r.scheme); err != nil {
+		if err = controllerutil.SetOwnerReference(buildWorkload, builder, r.scheme); err != nil {
 			log.Info("unable to set owner reference on Builder", "reason", err)
 			return err
 		}

kpack-image-builder/controllers/buildworkload_controller_test.go

@@ -258,6 +258,7 @@ var _ = Describe("BuildWorkloadReconciler", func() {
 					g.Expect(k8sClient.Get(ctx, client.ObjectKeyFromObject(builder), builder)).To(Succeed())
 					g.Expect(builder.OwnerReferences).To(HaveLen(1))
 					g.Expect(builder.OwnerReferences[0].Name).To(Equal(buildWorkload.Name))
+					g.Expect(builder.OwnerReferences[0].Controller).To(BeNil())
 
 					g.Expect(builder.Spec.Tag).To(Equal("my.repository/my-prefix/builders-" + builderName))
 					g.Expect(builder.Spec.Stack).To(Equal(clusterBuilder.Spec.Stack))
@@ -286,6 +287,41 @@ var _ = Describe("BuildWorkloadReconciler", func() {
 				}).Should(Succeed())
 			})
 
+			When("there is another buildworkload referencing the same buildpacks", func() {
+				var (
+					anotherBuildworkloadGUID string
+					sharedBuilder            *buildv1alpha2.Builder
+				)
+
+				BeforeEach(func() {
+					anotherBuildworkloadGUID = PrefixedGUID("another-buildworkload-")
+					anotherBuildWorkload := buildWorkloadObject(anotherBuildworkloadGUID, namespaceGUID, source, env, services, reconcilerName, buildpacks)
+					Expect(k8sClient.Create(ctx, anotherBuildWorkload)).To(Succeed())
+
+					sharedBuilder = &buildv1alpha2.Builder{
+						ObjectMeta: metav1.ObjectMeta{
+							Name:      controllers.ComputeBuilderName(anotherBuildWorkload.Spec.Buildpacks),
+							Namespace: namespaceGUID,
+						},
+					}
+					Eventually(func(g Gomega) {
+						g.Expect(k8sClient.Get(ctx, client.ObjectKeyFromObject(sharedBuilder), sharedBuilder)).To(Succeed())
+					}).Should(Succeed())
+				})
+
+				It("shares the kpack builder", func() {
+					Eventually(func(g Gomega) {
+						g.Expect(k8sClient.Get(ctx, client.ObjectKeyFromObject(sharedBuilder), sharedBuilder)).To(Succeed())
+						g.Expect(sharedBuilder.OwnerReferences).To(HaveLen(2))
+						g.Expect(
+							[]string{sharedBuilder.OwnerReferences[0].Name, sharedBuilder.OwnerReferences[1].Name},
+						).To(ConsistOf(
+							[]string{anotherBuildworkloadGUID, buildWorkloadGUID},
+						))
+					}).Should(Succeed())
+				})
+			})
+
 			When("a buildpack isn't in the default ClusterBuilder", func() {
 				BeforeEach(func() {
 					buildpacks = append(buildpacks, "not/in-the-store")