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GKE Control Plane should not be publicly accessible

Default Severity: high

Explanation

The GKE control plane is exposed to the public internet by default.

Possible Impact

GKE control plane exposed to public internet

Suggested Resolution

Use private nodes and master authorised networks to prevent exposure

Insecure Example

The following example will fail the google-gke-no-public-control-plane check. 

 resource "google_service_account" "default" {
   account_id   = "service-account-id"
   display_name = "Service Account"
 }

 resource "google_container_cluster" "primary" {
   name     = "my-gke-cluster"
   location = "us-central1"

   # We can't create a cluster with no node pool defined, but we want to only use
   # separately managed node pools. So we create the smallest possible default
   # node pool and immediately delete it.
   remove_default_node_pool = true
   initial_node_count       = 1
   master_authorized_networks_config {
     cidr_blocks {
       cidr_block = "0.0.0.0/0"
       display_name = "external"
     }
   }
 }

 resource "google_container_node_pool" "primary_preemptible_nodes" {
   name       = "my-node-pool"
   location   = "us-central1"
   cluster    = google_container_cluster.primary.name
   node_count = 1

   node_config {
     preemptible  = true
     machine_type = "e2-medium"

     # Google recommends custom service accounts that have cloud-platform scope and permissions granted via IAM Roles.
     service_account = google_service_account.default.email
     oauth_scopes    = [
       "https://www.googleapis.com/auth/cloud-platform"
     ]
   }
 }

Secure Example

The following example will pass the google-gke-no-public-control-plane check. 

 resource "google_service_account" "default" {
   account_id   = "service-account-id"
   display_name = "Service Account"
 }

 resource "google_container_cluster" "primary" {
   name     = "my-gke-cluster"
   location = "us-central1"

   # We can't create a cluster with no node pool defined, but we want to only use
   # separately managed node pools. So we create the smallest possible default
   # node pool and immediately delete it.
   remove_default_node_pool = true
   initial_node_count       = 1
   master_authorized_networks_config {
     cidr_blocks {
       cidr_block = "10.10.128.0/24"
       display_name = "internal"
     }
   }
 }

 resource "google_container_node_pool" "primary_preemptible_nodes" {
   name       = "my-node-pool"
   location   = "us-central1"
   cluster    = google_container_cluster.primary.name
   node_count = 1

   node_config {
     preemptible  = true
     machine_type = "e2-medium"

     # Google recommends custom service accounts that have cloud-platform scope and permissions granted via IAM Roles.
     service_account = google_service_account.default.email
     oauth_scopes    = [
       "https://www.googleapis.com/auth/cloud-platform"
     ]
   }
 }