Encrypting Secret Data at Rest

    • You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using or you can use one of these Kubernetes playgrounds:

      Your Kubernetes server must be at or later than version 1.13. To check the version, enter .

    • etcd v3.0 or later is required

    • To encrypt a custom resource, your cluster must be running Kubernetes v1.26 or newer.

    Configuration and determining whether encryption at rest is already enabled

    The kube-apiserver process accepts an argument --encryption-provider-config that controls how API data is encrypted in etcd. The configuration is provided as an API named . --encryption-provider-config-automatic-reload boolean argument determines if the file set by --encryption-provider-config should be automatically reloaded if the disk contents change. This enables key rotation without API server restarts. An example configuration is provided below.

    Caution: IMPORTANT: For high-availability configurations (with two or more control plane nodes), the encryption configuration file must be the same! Otherwise, the kube-apiserver component cannot decrypt data stored in the etcd.

    Understanding the encryption at rest configuration.

    Each resources array item is a separate config and contains a complete configuration. The resources.resources field is an array of Kubernetes resource names (resource or resource.group that should be encrypted like Secrets, ConfigMaps, or other resources.

    If custom resources are added to EncryptionConfiguration and the cluster version is 1.26 or newer, any newly created custom resources mentioned in the EncryptionConfiguration will be encrypted. Any custom resources that existed in etcd prior to that version and configuration will be unencrypted until they are next written to storage. This is the same behavior as built-in resources. See the section.

    The providers array is an ordered list of the possible encryption providers to use for the APIs that you listed.

    Only one provider type may be specified per entry (identity or aescbc may be provided, but not both in the same item). The first provider in the list is used to encrypt resources written into the storage. When reading resources from storage, each provider that matches the stored data attempts in order to decrypt the data. If no provider can read the stored data due to a mismatch in format or secret key, an error is returned which prevents clients from accessing that resource.

    For more detailed information about the EncryptionConfiguration struct, please refer to the encryption configuration API.

    Caution: If any resource is not readable via the encryption config (because keys were changed), the only recourse is to delete that key from the underlying etcd directly. Calls that attempt to read that resource will fail until it is deleted or a valid decryption key is provided.

    Each provider supports multiple keys - the keys are tried in order for decryption, and if the provider is the first provider, the first key is used for encryption.

    By default, the identity provider is used to protect secret data in etcd, which provides no encryption. EncryptionConfiguration was introduced to encrypt secret data locally, with a locally managed key.

    Encrypting secret data with a locally managed key protects against an etcd compromise, but it fails to protect against a host compromise. Since the encryption keys are stored on the host in the EncryptionConfiguration YAML file, a skilled attacker can access that file and extract the encryption keys.

    Envelope encryption creates dependence on a separate key, not stored in Kubernetes. In this case, an attacker would need to compromise etcd, the kubeapi-server, and the third-party KMS provider to retrieve the plaintext values, providing a higher level of security than locally stored encryption keys.

    Create a new encryption config file:

    1. apiVersion: apiserver.config.k8s.io/v1
    2. kind: EncryptionConfiguration
    3.   - resources:
    4.       - secrets
    5.       - configmaps
    6.       - pandas.awesome.bears.example
    7.     providers:
    8.       - aescbc:
    9.           keys:
    10.             - name: key1
    11.               secret: <BASE 64 ENCODED SECRET>
    12.       - identity: {}

    To create a new Secret, perform the following steps:

    1. Generate a 32-byte random key and base64 encode it. If you’re on Linux or macOS, run the following command:

      1. head -c 32 /dev/urandom | base64

    2. Place that value in the secret field of the EncryptionConfiguration struct.

    3. Set the --encryption-provider-config flag on the kube-apiserver to point to the location of the config file.

      You will need to mount the new encryption config file to the kube-apiserver static pod. Here is an example on how to do that:

      1. Save the new encryption config file to /etc/kubernetes/enc/enc.yaml on the control-plane node.
      2. Edit the manifest for the kube-apiserver static pod: /etc/kubernetes/manifests/kube-apiserver.yaml similarly to this:

    4. Restart your API server.

    Caution: Your config file contains keys that can decrypt the contents in etcd, so you must properly restrict permissions on your control-plane nodes so only the user who runs the kube-apiserver can read it.

    Verifying that data is encrypted

    Data is encrypted when written to etcd. After restarting your kube-apiserver, any newly created or updated Secret or other resource types configured in EncryptionConfiguration should be encrypted when stored. To check this, you can use the etcdctl command line program to retrieve the contents of your secret data.

    1. ETCDCTL_API=3 etcdctl get /registry/secrets/default/secret1 [...] | hexdump -C

      where [...] must be the additional arguments for connecting to the etcd server.

      For example:

      1. ETCDCTL_API=3 etcdctl \
      2.    --cacert=/etc/kubernetes/pki/etcd/ca.crt   \
      3.    --cert=/etc/kubernetes/pki/etcd/server.crt \
      4.    --key=/etc/kubernetes/pki/etcd/server.key  \
      5.    get /registry/secrets/default/secret1 | hexdump -C

      The output is similar to this (abbreviated):

    2. Verify the stored Secret is prefixed with k8s:enc:aescbc:v1: which indicates the aescbc provider has encrypted the resulting data. Confirm that the key name shown in etcd matches the key name specified in the EncryptionConfiguration mentioned above. In this example, you can see that the encryption key named key1 is used in etcd and in EncryptionConfiguration.

    3. Verify the Secret is correctly decrypted when retrieved via the API:

      1. kubectl get secret secret1 -n default -o yaml

      The output should contain mykey: bXlkYXRh, with contents of mydata encoded, check decoding a Secret to completely decode the Secret.

    Ensure all Secrets are encrypted

    Since Secrets are encrypted on write, performing an update on a Secret will encrypt that content.

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

    The command above reads all Secrets and then updates them to apply server side encryption.

    Note: If an error occurs due to a conflicting write, retry the command. For larger clusters, you may wish to subdivide the secrets by namespace or script an update.

    Changing a Secret without incurring downtime requires a multi-step operation, especially in the presence of a highly-available deployment where multiple kube-apiserver processes are running.

    1. Generate a new key and add it as the second key entry for the current provider on all servers
    2. Restart all kube-apiserver processes to ensure each server can decrypt using the new key
    3. Make the new key the first entry in the keys array so that it is used for encryption in the config
    4. Restart all kube-apiserver processes to ensure each server now encrypts using the new key
    5. Run kubectl get secrets --all-namespaces -o json | kubectl replace -f - to encrypt all existing Secrets with the new key
    6. Remove the old decryption key from the config after you have backed up etcd with the new key in use and updated all Secrets

    When running a single kube-apiserver instance, step 2 may be skipped.

    Decrypting all data

    To disable encryption at rest, place the identity provider as the first entry in the config and restart all kube-apiserver processes.

      What’s next

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