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Master authorized networks should be configured on GKE clusters

Default Severity: high

Explanation

Enabling authorized networks means you can restrict master access to a fixed set of CIDR ranges

Possible Impact

Unrestricted network access to the master

Suggested Resolution

Enable master authorized networks

Insecure Example

The following example will fail the google-gke-enable-master-networks 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
 }

 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-enable-master-networks 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"
     ]
   }
 }