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Add Key Management Service etcd encryption to an Azure Kubernetes Service cluster

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This article shows you how to turn on encryption at rest for your Azure Kubernetes Service (AKS) secrets in an etcd key-value store by using Azure Key Vault and the Key Management Service (KMS) plugin. You can use the KMS plugin to:

  • Use a key in a key vault for etcd encryption.
  • Bring your own keys.
  • Provide encryption at rest for secrets that are stored in etcd.
  • Rotate the keys in a key vault.

For more information on using KMS, see Encrypting Secret Data at Rest.

Prerequisites

Warning

KMS supports Konnectivity or API Server VNet Integration (preview).

You can use kubectl get po -n kube-system to verify the results and show that a konnectivity-agent pod is running. If a pod is running, the AKS cluster is using Konnectivity. When you use API Server VNet Integration, you can run the az aks show -g -n command to verify that the enableVnetIntegration setting is set to true.

Limitations

The following limitations apply when you integrate KMS etcd encryption with AKS:

  • Deleting the key, the key vault, or the associated identity isn't supported.
  • KMS etcd encryption doesn't work with system-assigned managed identity. The key vault access policy must be set before the feature is turned on. System-assigned managed identity isn't available until after the cluster is created. Consider the cycle dependency.
  • Azure Key Vault with a firewall to allow public access isn't supported because it blocks traffic from the KMS plugin to the key vault.
  • The maximum number of secrets that are supported by a cluster that has KMS turned on is 2,000. However, it's important to note that KMS v2 isn't limited by this restriction and can handle a higher number of secrets.
  • Bring your own (BYO) Azure key vault from another tenant isn't supported.
  • With KMS turned on, you can't change the associated key vault mode (public versus private). To update a key vault mode, you must first turn off KMS, and then turn it on again.
  • If a cluster has KMS turned on, has a private key vault, and isn't using the API Server VNet integration tunnel, you can't stop and then start the cluster.
  • Using the Virtual Machine Scale Sets API to scale the nodes in the cluster down to zero deallocates the nodes. The cluster then goes down and becomes unrecoverable.
  • After you turn off KMS, you can't destroy the keys. Destroying the keys causes the API server to stop working.

KMS supports a public key vault or a private key vault.

Turn on KMS for a public key vault

The following sections describe how to turn on KMS for a public key vault.

Create a public key vault and key

Warning

Deleting the key or the key vault is not supported and causes the secrets in the cluster to be unrecoverable.

If you need to recover your key vault or your key, see Azure Key Vault recovery management with soft delete and purge protection.

Create a key vault and key for a non-RBAC public key vault

Use az keyvault create to create a key vault without using Azure role-based access control (Azure RBAC):

az keyvault create --name MyKeyVault --resource-group MyResourceGroup

Use az keyvault key create to create a key:

az keyvault key create --name MyKeyName --vault-name MyKeyVault

Use az keyvault key show to export the key ID:

export KEY_ID=$(az keyvault key show --name MyKeyName --vault-name MyKeyVault --query 'key.kid' -o tsv)
echo $KEY_ID

This example stores the key ID in KEY_ID.

Create a key vault and key for an RBAC public key vault

Use az keyvault create to create a key vault by using Azure RBAC:

export KEYVAULT_RESOURCE_ID=$(az keyvault create --name MyKeyVault --resource-group MyResourceGroup  --enable-rbac-authorization true --query id -o tsv)

Assign yourself permissions to create a key:

az role assignment create --role "Key Vault Crypto Officer" --assignee-object-id $(az ad signed-in-user show --query id --out tsv) --assignee-principal-type "User" --scope $KEYVAULT_RESOURCE_ID

Use az keyvault key create to create a key:

az keyvault key create --name MyKeyName --vault-name MyKeyVault

Use az keyvault key show to export the key ID:

export KEY_ID=$(az keyvault key show --name MyKeyName --vault-name MyKeyVault --query 'key.kid' -o tsv)
echo $KEY_ID

This example stores the key ID in KEY_ID.

Create a user-assigned managed identity for a public key vault

Use az identity create to create a user-assigned managed identity:

az identity create --name MyIdentity --resource-group MyResourceGroup

Use az identity show to get the identity object ID:

IDENTITY_OBJECT_ID=$(az identity show --name MyIdentity --resource-group MyResourceGroup --query 'principalId' -o tsv)
echo $IDENTITY_OBJECT_ID

The preceding example stores the value of the identity object ID in IDENTITY_OBJECT_ID.

Use az identity show to get the identity resource ID:

IDENTITY_RESOURCE_ID=$(az identity show --name MyIdentity --resource-group MyResourceGroup --query 'id' -o tsv)
echo $IDENTITY_RESOURCE_ID

This example stores the value of the identity resource ID in IDENTITY_RESOURCE_ID.

Assign permissions to decrypt and encrypt a public key vault

The following sections describe how to assign decrypt and encrypt permissions for a private key vault.

Assign permissions for a non-RBAC public key vault

If your key vault is not set with --enable-rbac-authorization, you can use az keyvault set-policy to create an Azure key vault policy.

az keyvault set-policy -n MyKeyVault --key-permissions decrypt encrypt --object-id $IDENTITY_OBJECT_ID

Assign permissions for an RBAC public key vault

If your key vault is set with --enable-rbac-authorization, assign the Key Vault Crypto User role to give decrypt and encrypt permissions.

az role assignment create --role "Key Vault Crypto User" --assignee-object-id $IDENTITY_OBJECT_ID --assignee-principal-type "ServicePrincipal" --scope $KEYVAULT_RESOURCE_ID

Create an AKS cluster that has a public key vault and turn on KMS etcd encryption

To turn on KMS etcd encryption, create an AKS cluster by using the az aks create command. You can use the --enable-azure-keyvault-kms, --azure-keyvault-kms-key-vault-network-access, and --azure-keyvault-kms-key-id parameters with az aks create.

az aks create --name myAKSCluster --resource-group MyResourceGroup --assign-identity $IDENTITY_RESOURCE_ID --enable-azure-keyvault-kms --azure-keyvault-kms-key-vault-network-access "Public" --azure-keyvault-kms-key-id $KEY_ID

Update an existing AKS cluster to turn on KMS etcd encryption for a public key vault

To turn on KMS etcd encryption for an existing cluster, use the az aks update command. You can use the --enable-azure-keyvault-kms, --azure-keyvault-kms-key-vault-network-access, and --azure-keyvault-kms-key-id parameters with az-aks-update.

az aks update --name myAKSCluster --resource-group MyResourceGroup --enable-azure-keyvault-kms --azure-keyvault-kms-key-vault-network-access "Public" --azure-keyvault-kms-key-id $KEY_ID

Use the following command to update all secrets. If you don't run this command, secrets that were created earlier are no longer encrypted. For larger clusters, you might want to subdivide the secrets by namespace or create an update script.

kubectl get secrets --all-namespaces -o json | kubectl replace -f -

Rotate existing keys in a public key vault

After you change the key ID (including changing either the key name or the key version), you can use the az aks update command. You can use the --enable-azure-keyvault-kms, --azure-keyvault-kms-key-vault-network-access, and --azure-keyvault-kms-key-id parameters with az-aks-update to rotate existing keys in KMS.

Warning

Remember to update all secrets after key rotation. If you don't update all secrets, the secrets are inaccessible if the keys that were created earlier don't exist or no longer work.

After you rotate the key, the previous key (key1) is still cached and shouldn't be deleted. If you want to delete the previous key (key1) immediately, you need to rotate the key twice. Then key2 and key3 are cached, and key1 can be deleted without affecting the existing cluster.

az aks update --name myAKSCluster --resource-group MyResourceGroup  --enable-azure-keyvault-kms --azure-keyvault-kms-key-vault-network-access "Public" --azure-keyvault-kms-key-id $NEW_KEY_ID

Use the following command to update all secrets. If you don't run this command, secrets that were created earlier are still encrypted with the previous key. For larger clusters, you might want to subdivide the secrets by namespace or create an update script.

kubectl get secrets --all-namespaces -o json | kubectl replace -f -

Turn on KMS for a private key vault

If you turn on KMS for a private key vault, AKS automatically creates a private endpoint and a private link in the node resource group. The key vault is added a private endpoint connection with the AKS cluster.

Create a private key vault and key

Warning

Deleting the key or the key vault is not supported and causes the secrets in the cluster to be unrecoverable.

If you need to recover your key vault or your key, see Azure Key Vault recovery management with soft delete and purge protection.

Use az keyvault create to create a private key vault:

az keyvault create --name MyKeyVault --resource-group MyResourceGroup --public-network-access Disabled

Creating or updating keys in a private key vault that doesn't have a private endpoint isn't supported. To learn how to manage private key vaults, see Integrate a key vault by using Azure Private Link.

Create a user-assigned managed identity for a private key vault

Use az identity create to create a user-assigned managed identity:

az identity create --name MyIdentity --resource-group MyResourceGroup

Use az identity show to get the identity object ID:

IDENTITY_OBJECT_ID=$(az identity show --name MyIdentity --resource-group MyResourceGroup --query 'principalId' -o tsv)
echo $IDENTITY_OBJECT_ID

The preceding example stores the value of the identity object ID in IDENTITY_OBJECT_ID.

Use az identity show to get the identity resource ID:

IDENTITY_RESOURCE_ID=$(az identity show --name MyIdentity --resource-group MyResourceGroup --query 'id' -o tsv)
echo $IDENTITY_RESOURCE_ID

This example stores the value of the identity resource ID in IDENTITY_RESOURCE_ID.

Assign permissions to decrypt and encrypt a private key vault

The following sections describe how to assign decrypt and encrypt permissions for a private key vault.

Assign permissions for a non-RBAC private key vault

Note

When using a private key vault, AKS can't validate the permissions of the identity. Verify the identity has been granted permission to access the key vault before enabling KMS.

If your key vault is not set with --enable-rbac-authorization, you can use az keyvault set-policy to create a key vault policy in Azure:

az keyvault set-policy -n MyKeyVault --key-permissions decrypt encrypt --object-id $IDENTITY_OBJECT_ID

Assign permissions for an RBAC private key vault

If your key vault is set with --enable-rbac-authorization, assign an Azure RBAC role that includes decrypt and encrypt permissions:

az role assignment create --role "Key Vault Crypto User" --assignee-object-id $IDENTITY_OBJECT_ID --assignee-principal-type "ServicePrincipal" --scope $KEYVAULT_RESOURCE_ID

For private key vaults, the Key Vault Contributor role is required to create a private link between the private key vault and the cluster.

az role assignment create --role "Key Vault Contributor" --assignee-object-id $IDENTITY_OBJECT_ID --assignee-principal-type "ServicePrincipal" --scope $KEYVAULT_RESOURCE_ID

Create an AKS cluster that has a private key vault and turn on KMS etcd encryption

To turn on KMS etcd encryption for a private key vault, create an AKS cluster by using the az aks create command. You can use the --enable-azure-keyvault-kms, --azure-keyvault-kms-key-id, --azure-keyvault-kms-key-vault-network-access, and --azure-keyvault-kms-key-vault-resource-id parameters with az-aks-create.

az aks create --name myAKSCluster --resource-group MyResourceGroup --assign-identity $IDENTITY_RESOURCE_ID --enable-azure-keyvault-kms --azure-keyvault-kms-key-id $KEY_ID --azure-keyvault-kms-key-vault-network-access "Private" --azure-keyvault-kms-key-vault-resource-id $KEYVAULT_RESOURCE_ID

Update an existing AKS cluster to turn on KMS etcd encryption for a private key vault

To turn on KMS etcd encryption on an existing cluster that has a private key vault, use the az aks update command. You can use the --enable-azure-keyvault-kms, --azure-keyvault-kms-key-id, --azure-keyvault-kms-key-vault-network-access, and --azure-keyvault-kms-key-vault-resource-id parameters with az-aks-update.

az aks update --name myAKSCluster --resource-group MyResourceGroup --enable-azure-keyvault-kms --azure-keyvault-kms-key-id $KEY_ID --azure-keyvault-kms-key-vault-network-access "Private" --azure-keyvault-kms-key-vault-resource-id $KEYVAULT_RESOURCE_ID

Use the following command to update all secrets. If you don't run this command, secrets that were created earlier aren't encrypted. For larger clusters, you might want to subdivide the secrets by namespace or create an update script.

kubectl get secrets --all-namespaces -o json | kubectl replace -f -

Rotate existing keys in a private key vault

After you change the key ID (including the key name and the key version), you can use the az aks update command. You can use the --enable-azure-keyvault-kms, --azure-keyvault-kms-key-id, --azure-keyvault-kms-key-vault-network-access, and --azure-keyvault-kms-key-vault-resource-id parameters with az-aks-update to rotate the existing keys of KMS.

Warning

Remember to update all secrets after key rotation. If you don't update all secrets, the secrets are inaccessible if the keys that were created earlier don't exist or no longer work.

After you rotate the key, the previous key (key1) is still cached and shouldn't be deleted. If you want to delete the previous key (key1) immediately, you need to rotate the key twice. Then key2 and key3 are cached, and key1 can be deleted without affecting the existing cluster.

az aks update --name myAKSCluster --resource-group MyResourceGroup  --enable-azure-keyvault-kms --azure-keyvault-kms-key-id $NewKEY_ID --azure-keyvault-kms-key-vault-network-access "Private" --azure-keyvault-kms-key-vault-resource-id $KEYVAULT_RESOURCE_ID

Use the following command to update all secrets. If you don't update all secrets, secrets that were created earlier are encrypted with the previous key. For larger clusters, you might want to subdivide the secrets by namespace or create an update script.

kubectl get secrets --all-namespaces -o json | kubectl replace -f -

Update a key vault mode

Note

To change a different key vault with a different mode (whether public or private), you can run az aks update directly. To change the mode of an attached key vault, you must first turn off KMS, and then turn it on again by using the new key vault IDs.

The following sections describe how to migrate an attached public key vault to private mode.

Turn off KMS on the cluster

Turn off KMS on an existing cluster and release the key vault:

az aks update --name myAKSCluster --resource-group MyResourceGroup --disable-azure-keyvault-kms

Change the key vault mode

Update the key vault from public to private:

az keyvault update --name MyKeyVault --resource-group MyResourceGroup --public-network-access Disabled

Turn on KMS for the cluster by using the updated key vault

Turn on KMS by using the updated private key vault:

az aks update --name myAKSCluster --resource-group MyResourceGroup  --enable-azure-keyvault-kms --azure-keyvault-kms-key-id $NewKEY_ID --azure-keyvault-kms-key-vault-network-access "Private" --azure-keyvault-kms-key-vault-resource-id $KEYVAULT_RESOURCE_ID

After you set up KMS, you can turn on diagnostic settings for the key vault to check the encryption logs.

Turn off KMS

Before you turn off KMS, you can use the following Azure CLI command to check whether KMS is turned on:

az aks list --query "[].{Name:name, KmsEnabled:securityProfile.azureKeyVaultKms.enabled, KeyId:securityProfile.azureKeyVaultKms.keyId}" -o table

If the results confirm KMS that is on, run the following command to turn off KMS on the cluster:

az aks update --name myAKSCluster --resource-group MyResourceGroup --disable-azure-keyvault-kms

Use the following command to update all secrets. If you don't run this command, secrets that were created earlier are still encrypted with the previous key, and the encrypt and decrypt permissions on the key vault are still required. For larger clusters, you might want to subdivide the secrets by namespace or create an update script.

kubectl get secrets --all-namespaces -o json | kubectl replace -f -

KMS v2 support

Beginning in AKS version 1.27, turning on the KMS feature configures KMS v2. With KMS v2, you aren't limited to the 2,000 secrets that earlier versions support. For more information, see KMS V2 Improvements.

Migrate to KMS v2

If your cluster version is later than 1.27 and you already turned on KMS, the upgrade to KMS 1.27 or later is blocked. Use the following steps to migrate to KMS v2:

  1. Turn off KMS on the cluster.
  2. Perform the storage migration.
  3. Upgrade the cluster to version 1.27 or later.
  4. Turn on KMS on the cluster.
  5. Perform the storage migration.

Turn off KMS to migrate storage

To turn off KMS on an existing cluster, use the az aks update command with the --disable-azure-keyvault-kms argument:

az aks update --name myAKSCluster --resource-group MyResourceGroup --disable-azure-keyvault-kms

Migrate storage

To update all secrets, use the kubectl get secrets command with the --all-namespaces argument:

kubectl get secrets --all-namespaces -o json | kubectl replace -f -

Upgrade the AKS cluster

To upgrade an AKS cluster, use the az aks upgrade command. Set the version to 1.27.x or later by using the --kubernetes-version argument.

az aks upgrade --resource-group myResourceGroup --name myAKSCluster --kubernetes-version <AKS version>

Here's an example:

az aks upgrade --resource-group myResourceGroup --name myAKSCluster --kubernetes-version 1.27.1

Turn on KMS after storage migration

You can turn on the KMS feature on the cluster again to encrypt the secrets. Afterward, the AKS cluster uses KMS v2. If you don't want to migrate to KMS v2, you can create a new cluster that is version 1.27 or later with KMS turned on.

Migrate storage for KMS v2

To re-encrypt all secrets in KMS v2, use the kubectl get secrets command with the --all-namespaces argument:

kubectl get secrets --all-namespaces -o json | kubectl replace -f -