diff --git a/README.md b/README.md
index 85a13b3..04cb191 100644
--- a/README.md
+++ b/README.md
@@ -37,4 +37,3 @@ resource local_file "assets" {
   content = each.value
 }
 ```
-
diff --git a/variables.tf b/variables.tf
index 9c75f20..376def0 100644
--- a/variables.tf
+++ b/variables.tf
@@ -13,6 +13,8 @@ variable "etcd_servers" {
   description = "List of URLs used to reach etcd servers."
 }
 
+# optional
+
 variable "networking" {
   type        = string
   description = "Choice of networking provider (flannel or calico or cilium)"
@@ -65,10 +67,10 @@ variable "container_images" {
     coredns                 = "k8s.gcr.io/coredns/coredns:v1.8.6"
     flannel                 = "quay.io/coreos/flannel:v0.15.1"
     flannel_cni             = "quay.io/poseidon/flannel-cni:v0.4.2"
-    kube_apiserver          = "k8s.gcr.io/kube-apiserver:v1.22.4"
-    kube_controller_manager = "k8s.gcr.io/kube-controller-manager:v1.22.4"
-    kube_scheduler          = "k8s.gcr.io/kube-scheduler:v1.22.4"
-    kube_proxy              = "k8s.gcr.io/kube-proxy:v1.22.4"
+    kube_apiserver          = "k8s.gcr.io/kube-apiserver:v1.23.0"
+    kube_controller_manager = "k8s.gcr.io/kube-controller-manager:v1.23.0"
+    kube_scheduler          = "k8s.gcr.io/kube-scheduler:v1.23.0"
+    kube_proxy              = "k8s.gcr.io/kube-proxy:v1.23.0"
   }
 }