Encryption at rest

Kubernetes has the concept of secrets for managing sensitive information needed by a cluster, such as usernames and passwords, encryption keys, etc. Secrets can be managed independently of the pod(s) which need them and can be made available to the pods that require them as needed.

By default, the secret data is stored in plaintext in etcd. Kubernetes does support encryption at rest for the data in etcd, but the key for that encryption is stored in plaintext in the config file on the master nodes. To protect this key at rest, Charmed Kubernetes can use HashiCorp’s Vault and VaultLocker to securely generate, share, and configure the encryption key used by Kubernetes.

Using Encryption-at-Rest with Charmed Kubernetes

To enable encryption-at-rest for Charmed Kubernetes, simply deploy the Vault charm (as well as a database backend for it), and relate it to kubernetes-master via the vault-kv relation endpoint. The easiest way to do this is to deploy Charmed Kubernetes with the following overlay:

applications:
  vault:
    charm: cs:vault
    num_units: 1
  percona-cluster:
    charm: cs:percona-cluster
    num_units: 1
relations:
  - ['vault', 'percona-cluster']
  - ['vault:secrets', 'kubernetes-master:vault-kv']

To deploy Charmed Kubernetes with this overlay - download it), save it as, e.g., cdk-vault-overlay.yaml, and deploy with:

juju deploy charmed-kubernetes --overlay cdk-vault-overlay.yaml

Once Vault comes up (and any time it is rebooted), you will need to unseal it.

Charmed Kubernetes will then automatically enable encryption for the secrets data stored in etcd.

Known Issues

This does not work on LXD at this time, due to security limitations preventing charms from acquiring and managing the block devices and file systems needed to implement this. In the future, support for KMS, or encryption-as-a-service, will remove this restriction. In the meantime, LXD deployments can make use of encryption at the level of the LXD storage pool, or even full-disk-encryption on the host machine.