diff --git a/api/openapi-spec/swagger.json b/api/openapi-spec/swagger.json
index b14dc823f2..c8130b40ac 100644
--- a/api/openapi-spec/swagger.json
+++ b/api/openapi-spec/swagger.json
@@ -85395,7 +85395,6 @@
     "description": "APIServiceSpec contains information for locating and communicating with a server. Only https is supported, though you are able to disable certificate verification.",
     "required": [
      "service",
-     "caBundle",
      "groupPriorityMinimum",
      "versionPriority"
     ],
@@ -85541,7 +85540,6 @@
     "description": "APIServiceSpec contains information for locating and communicating with a server. Only https is supported, though you are able to disable certificate verification.",
     "required": [
      "service",
-     "caBundle",
      "groupPriorityMinimum",
      "versionPriority"
     ],
diff --git a/staging/src/k8s.io/kube-aggregator/pkg/apis/apiregistration/types.go b/staging/src/k8s.io/kube-aggregator/pkg/apis/apiregistration/types.go
index 853d015206..d052361c73 100644
--- a/staging/src/k8s.io/kube-aggregator/pkg/apis/apiregistration/types.go
+++ b/staging/src/k8s.io/kube-aggregator/pkg/apis/apiregistration/types.go
@@ -53,6 +53,7 @@ type APIServiceSpec struct {
 	// This is strongly discouraged.  You should use the CABundle instead.
 	InsecureSkipTLSVerify bool
 	// CABundle is a PEM encoded CA bundle which will be used to validate an API server's serving certificate.
+	// +optional
 	CABundle []byte
 
 	// GroupPriorityMininum is the priority this group should have at least. Higher priority means that the group is preferred by clients over lower priority ones.
diff --git a/staging/src/k8s.io/kube-aggregator/pkg/apis/apiregistration/v1/generated.proto b/staging/src/k8s.io/kube-aggregator/pkg/apis/apiregistration/v1/generated.proto
index 8ae9141942..b00a12e51c 100644
--- a/staging/src/k8s.io/kube-aggregator/pkg/apis/apiregistration/v1/generated.proto
+++ b/staging/src/k8s.io/kube-aggregator/pkg/apis/apiregistration/v1/generated.proto
@@ -89,6 +89,7 @@ message APIServiceSpec {
   optional bool insecureSkipTLSVerify = 4;
 
   // CABundle is a PEM encoded CA bundle which will be used to validate an API server's serving certificate.
+  // +optional
   optional bytes caBundle = 5;
 
   // GroupPriorityMininum is the priority this group should have at least. Higher priority means that the group is preferred by clients over lower priority ones.
diff --git a/staging/src/k8s.io/kube-aggregator/pkg/apis/apiregistration/v1/types.go b/staging/src/k8s.io/kube-aggregator/pkg/apis/apiregistration/v1/types.go
index a545c3bde0..4e2a931825 100644
--- a/staging/src/k8s.io/kube-aggregator/pkg/apis/apiregistration/v1/types.go
+++ b/staging/src/k8s.io/kube-aggregator/pkg/apis/apiregistration/v1/types.go
@@ -53,7 +53,8 @@ type APIServiceSpec struct {
 	// This is strongly discouraged.  You should use the CABundle instead.
 	InsecureSkipTLSVerify bool `json:"insecureSkipTLSVerify,omitempty" protobuf:"varint,4,opt,name=insecureSkipTLSVerify"`
 	// CABundle is a PEM encoded CA bundle which will be used to validate an API server's serving certificate.
-	CABundle []byte `json:"caBundle" protobuf:"bytes,5,opt,name=caBundle"`
+	// +optional
+	CABundle []byte `json:"caBundle,omitempty" protobuf:"bytes,5,opt,name=caBundle"`
 
 	// GroupPriorityMininum is the priority this group should have at least. Higher priority means that the group is preferred by clients over lower priority ones.
 	// Note that other versions of this group might specify even higher GroupPriorityMininum values such that the whole group gets a higher priority.
diff --git a/staging/src/k8s.io/kube-aggregator/pkg/apis/apiregistration/v1beta1/generated.proto b/staging/src/k8s.io/kube-aggregator/pkg/apis/apiregistration/v1beta1/generated.proto
index 23c7118ffb..13c1126dd6 100644
--- a/staging/src/k8s.io/kube-aggregator/pkg/apis/apiregistration/v1beta1/generated.proto
+++ b/staging/src/k8s.io/kube-aggregator/pkg/apis/apiregistration/v1beta1/generated.proto
@@ -89,6 +89,7 @@ message APIServiceSpec {
   optional bool insecureSkipTLSVerify = 4;
 
   // CABundle is a PEM encoded CA bundle which will be used to validate an API server's serving certificate.
+  // +optional
   optional bytes caBundle = 5;
 
   // GroupPriorityMininum is the priority this group should have at least. Higher priority means that the group is preferred by clients over lower priority ones.
diff --git a/staging/src/k8s.io/kube-aggregator/pkg/apis/apiregistration/v1beta1/types.go b/staging/src/k8s.io/kube-aggregator/pkg/apis/apiregistration/v1beta1/types.go
index 2ac807e39c..0652d50904 100644
--- a/staging/src/k8s.io/kube-aggregator/pkg/apis/apiregistration/v1beta1/types.go
+++ b/staging/src/k8s.io/kube-aggregator/pkg/apis/apiregistration/v1beta1/types.go
@@ -53,7 +53,8 @@ type APIServiceSpec struct {
 	// This is strongly discouraged.  You should use the CABundle instead.
 	InsecureSkipTLSVerify bool `json:"insecureSkipTLSVerify,omitempty" protobuf:"varint,4,opt,name=insecureSkipTLSVerify"`
 	// CABundle is a PEM encoded CA bundle which will be used to validate an API server's serving certificate.
-	CABundle []byte `json:"caBundle" protobuf:"bytes,5,opt,name=caBundle"`
+	// +optional
+	CABundle []byte `json:"caBundle,omitempty" protobuf:"bytes,5,opt,name=caBundle"`
 
 	// GroupPriorityMininum is the priority this group should have at least. Higher priority means that the group is preferred by clients over lower priority ones.
 	// Note that other versions of this group might specify even higher GroupPriorityMininum values such that the whole group gets a higher priority.