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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 base64-encoded 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 control plane 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-control-plane via the vault-kv relation endpoint.

The following overlay file (download) alters Charmed Kubernetes to use Vault for encrypted data:

applications:
  mysql-innodb-cluster:
    channel: 8.0/stable
    charm: mysql-innodb-cluster
    constraints: cores=2 mem=8G root-disk=64G
    num_units: 3
    options:
      enable-binlogs: true
      innodb-buffer-pool-size: 256M
      max-connections: 2000
      wait-timeout: 3600
  vault:
    channel: 1.7/stable
    charm: vault
    num_units: 1
  vault-mysql-router:
    channel: 8.0/stable
    charm: mysql-router
relations:
- - kubernetes-control-plane:vault-kv
  - vault:secrets
- - mysql-innodb-cluster:db-router
  - vault-mysql-router:db-router
- - vault-mysql-router:shared-db
  - vault:shared-db

Save this to a file named vault-storage-overlay.yaml and deploy with:

juju deploy charmed-kubernetes --overlay ./vault-storage-overlay.yaml

Once the deployment settles, you will notice that several applications are in a blocked state in Juju, with Vault indicating that it needs to be initialised and unsealed. To unseal Vault, you can read the vault charm documentation for in-depth instructions (you may also need to expose Vault), or you can use the Vault client already on the deployed unit with the following steps:

juju ssh vault/0
export HISTCONTROL=ignorespace  # enable leading space to suppress command history
export VAULT_ADDR='http://localhost:8200'
vault operator init -key-shares=5 -key-threshold=3  # outputs 5 keys and a root token
 vault operator unseal {key1}
 vault operator unseal {key2}
 vault operator unseal {key3}
 VAULT_TOKEN={root token} vault token create -ttl 10m  # outputs a {charm token} to auth the charm
exit
juju run-action vault/0 authorize-charm token={charm token} --wait

It is critical that you save all five unseal keys as well as the root token. If the Vault unit is ever rebooted, you will have to repeat the unseal steps (but not the init step) before the CA can become functional again.

Once the deployment settles, Charmed Kubernetes will 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.

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