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Use Customer-Managed Encryption Keys (CMEK) to encrypt node boot disks using keys managed within Cloud Key Management Service (Cloud KMS).
GCE persistent disks are encrypted at rest by default using envelope encryption with keys managed by Google. For additional protection, users can manage the Key Encryption Keys using Cloud KMS.
Note
Note
Persistent disks are encrypted at rest by default, but are not encrypted using Customer-Managed Encryption Keys by default. By default, the Compute Engine Persistent Disk CSI Driver is not provisioned within the cluster.

Impact

Encryption of dynamically-provisioned attached disks requires the use of the self-provisioned Compute Engine Persistent Disk CSI Driver v0.5.1 or higher.
If CMEK is being configured with a regional cluster, the cluster must run GKE 1.14 or higher.

Audit

Using Google Cloud Console:
  1. Go to Kubernetes Engine website.
  2. Click on each cluster, and click on any Node pools.
  3. On the Node pool Details page, under the Security heading, check that Boot disk encryption type is set to Customer managed with the desired key.
Using Command Line:
Run this command: 
gcloud container node-pools describe $NODE_POOL --cluster $CLUSTER_NAME 
--zone $COMPUTE_ZONE
Verify that the output of the above command includes a diskType of either pd-standard, pd-balanced, or pd-ssd, and the bootDiskKmsKey is specified as the desired key.

Remediation

This cannot be remediated by updating an existing cluster. The node pool must either be recreated or a new cluster created.
Using Google Cloud Console:
To create a new node pool:
  1. Go to Kubernetes Engine website.
  2. Select Kubernetes clusters for which node boot disk CMEK is disabled.
  3. Click ADD NODE POOL.
  4. In the Nodes section, under machine configuration, ensure Boot disk type is Standard persistent disk or SSD persistent disk.
  5. Select Enable customer-managed encryption for Boot Disk and select the Cloud KMS encryption key to be used.
  6. Click CREATE.
To create a new cluster:
  1. Go to Kubernetes Engine website.
  2. Click CREATE and click CONFIGURE for the required cluster mode.
  3. Under NODE POOLS, expand the default-pool list and click Nodes.
  4. In the Configure node settings pane, select Standard persistent disk or SSD Persistent Disk as the Boot disk type.
  5. Select Enable customer-managed encryption for Boot Disk check box and choose the Cloud KMS encryption key to be used.
  6. Configure the rest of the cluster settings as required.
  7. Click CREATE.
Using Command Line:
Create a new node pool using customer-managed encryption keys for the node boot disk, of <disk_type> either pd-standard or pd-ssd: 
gcloud container node-pools create <cluster_name> --disk-type <disk_type> 
--boot-disk-kms-key 
projects/<key_project_id>/locations/<location>/keyRings/<ring_name>
/cryptoKeys/<key_name>
Create a cluster using customer-managed encryption keys for the node boot disk, of <disk_type> either pd-standard or pd-ssd:
gcloud container clusters create <cluster_name> --disk-type <disk_type> 
--boot-disk-kms-key 
projects/<key_project_id>/locations/<location>/keyRings/<ring_name>
/cryptoKeys/<key_name>