diff --git a/README.md b/README.md
index cf0deeb2..ad713bc9 100644
--- a/README.md
+++ b/README.md
@@ -47,26 +47,25 @@ module "google-cloud-yavin" {
   source = "git::https://github.com/poseidon/typhoon//google-cloud/container-linux/kubernetes?ref=v1.9.6"
   
   providers = {
-    google = "google.default"
-    local = "local.default"
-    null = "null.default"
+    google   = "google.default"
+    local    = "local.default"
+    null     = "null.default"
     template = "template.default"
-    tls = "tls.default"
+    tls      = "tls.default"
   }
 
   # Google Cloud
+  cluster_name  = "yavin"
   region        = "us-central1"
   dns_zone      = "example.com"
   dns_zone_name = "example-zone"
-  os_image      = "coreos-stable"
 
-  cluster_name       = "yavin"
-  controller_count   = 1
-  worker_count       = 2
+  # configuration
   ssh_authorized_key = "ssh-rsa AAAAB3Nz..."
-
-  # output assets dir
-  asset_dir = "/home/user/.secrets/clusters/yavin"
+  asset_dir          = "/home/user/.secrets/clusters/yavin"
+  
+  # optional
+  worker_count = 2
 }
 ```
 
diff --git a/docs/aws.md b/docs/aws.md
index 4dd8e049..37d31f29 100644
--- a/docs/aws.md
+++ b/docs/aws.md
@@ -105,20 +105,19 @@ module "aws-tempest" {
     template = "template.default"
     tls = "tls.default"
   }
-  
-  cluster_name = "tempest"
 
   # AWS
-  dns_zone           = "aws.example.com"
-  dns_zone_id        = "Z3PAABBCFAKEC0"
-  controller_count   = 1
-  controller_type    = "t2.medium"
-  worker_count       = 2
-  worker_type        = "t2.small"
-  ssh_authorized_key = "ssh-rsa AAAAB3Nz..."
+  cluster_name = "tempest"
+  dns_zone     = "aws.example.com"
+  dns_zone_id  = "Z3PAABBCFAKEC0"
 
-  # bootkube
-  asset_dir  = "/home/user/.secrets/clusters/tempest"
+  # configuration
+  ssh_authorized_key = "ssh-rsa AAAAB3Nz..."
+  asset_dir          = "/home/user/.secrets/clusters/tempest"
+
+  # optional
+  worker_count = 2
+  worker_type  = "t2.medium"
 }
 ```
 
diff --git a/docs/bare-metal.md b/docs/bare-metal.md
index a5c16e1a..6c733557 100644
--- a/docs/bare-metal.md
+++ b/docs/bare-metal.md
@@ -190,11 +190,12 @@ module "bare-metal-mercury" {
   matchbox_http_endpoint  = "http://matchbox.example.com"
   container_linux_channel = "stable"
   container_linux_version = "1632.3.0"
-  ssh_authorized_key      = "ssh-rsa AAAAB3Nz..."
 
-  # cluster
-  cluster_name    = "mercury"
-  k8s_domain_name = "node1.example.com"
+  # configuration
+  cluster_name       = "mercury"
+  k8s_domain_name    = "node1.example.com"
+  ssh_authorized_key = "ssh-rsa AAAAB3Nz..."
+  asset_dir          = "/home/user/.secrets/clusters/mercury"
 
   # machines
   controller_names   = ["node1"]
@@ -212,9 +213,6 @@ module "bare-metal-mercury" {
     "node2.example.com",
     "node3.example.com",
   ]
-
-  # output assets dir
-  asset_dir = "/home/user/.secrets/clusters/mercury"
 }
 ```
 
diff --git a/docs/digital-ocean.md b/docs/digital-ocean.md
index cf367fe5..d47d2599 100644
--- a/docs/digital-ocean.md
+++ b/docs/digital-ocean.md
@@ -100,19 +100,18 @@ module "digital-ocean-nemo" {
     tls = "tls.default"
   }
 
-  region   = "nyc3"
-  dns_zone = "digital-ocean.example.com"
+  # Digital Ocean
+  cluster_name = "nemo"
+  region       = "nyc3"
+  dns_zone     = "digital-ocean.example.com"
 
-  cluster_name     = "nemo"
-  image            = "coreos-stable"
-  controller_count = 1
-  controller_type  = "s-2vcpu-2gb"
-  worker_count     = 2
-  worker_type      = "s-1vcpu-1gb"
+  # configuration
   ssh_fingerprints = ["d7:9d:79:ae:56:32:73:79:95:88:e3:a2:ab:5d:45:e7"]
-
-  # output assets dir
-  asset_dir = "/home/user/.secrets/clusters/nemo"
+  asset_dir        = "/home/user/.secrets/clusters/nemo"
+  
+  # optional
+  worker_count = 2
+  worker_type  = "s-1vcpu-1gb"
 }
 ```
 
diff --git a/docs/google-cloud.md b/docs/google-cloud.md
index bf0d4bf1..866fbdb5 100644
--- a/docs/google-cloud.md
+++ b/docs/google-cloud.md
@@ -108,18 +108,17 @@ module "google-cloud-yavin" {
   }
 
   # Google Cloud
+  cluster_name  = "yavin"
   region        = "us-central1"
   dns_zone      = "example.com"
   dns_zone_name = "example-zone"
-  os_image      = "coreos-stable"
 
-  cluster_name       = "yavin"
-  controller_count   = 1
-  worker_count       = 2
+  # configuration
   ssh_authorized_key = "ssh-rsa AAAAB3Nz..."
-
-  # output assets dir
-  asset_dir = "/home/user/.secrets/clusters/yavin"
+  asset_dir          = "/home/user/.secrets/clusters/yavin"
+  
+  # optional
+  worker_count = 2
 }
 ```
 
diff --git a/docs/index.md b/docs/index.md
index 52fc49d9..cc64ea43 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -47,26 +47,25 @@ module "google-cloud-yavin" {
   source = "git::https://github.com/poseidon/typhoon//google-cloud/container-linux/kubernetes?ref=v1.9.6"
   
   providers = {
-    google = "google.default"
-    local = "local.default"
-    null = "null.default"
+    google   = "google.default"
+    local    = "local.default"
+    null     = "null.default"
     template = "template.default"
-    tls = "tls.default"
+    tls      = "tls.default"
   }
 
   # Google Cloud
+  cluster_name  = "yavin"
   region        = "us-central1"
   dns_zone      = "example.com"
   dns_zone_name = "example-zone"
-  os_image      = "coreos-stable"
 
-  cluster_name       = "yavin"
-  controller_count   = 1
-  worker_count       = 2
+  # configuration
   ssh_authorized_key = "ssh-rsa AAAAB3Nz..."
-
-  # output assets dir
-  asset_dir = "/home/user/.secrets/clusters/yavin"
+  asset_dir          = "/home/user/.secrets/clusters/yavin"
+  
+  # optional
+  worker_count = 2
 }
 ```