Using Vault as a CA

As mentioned in the Certificates and trust reference documentation, HashiCorp's Vault can be used to provide either a root or intermediate CA. It can also be deployed HA, as well as provide a secure secrets store which can be used to enable encryption-at-rest for Charmed Kubernetes.

Vault does require an additional database to store its data and (depending on configuration) some manual steps will be required after deployment or any reboot so that secrets, such as certificates and signing keys, can be accessed.

Deploying Charmed Kubernetes with Vault as a root CA

When deploying Charmed Kubernetes manually via the published Juju bundle, it is possible to make use of an overlay file to change the composition and configuration of the cluster.

The following overlay file (download) alters Charmed Kubernetes to use Vault instead of EasyRSA:

applications:
  easyrsa:
    # it's currently not possible to remove an application in an overlay
    num_units: 0
  vault:
    charm: cs:~openstack-charmers-next/vault
    num_units: 1
    options:
      # this makes Vault act as a self-signed root CA
      auto-generate-root-ca-cert: true
  percona-cluster:
    charm: cs:percona-cluster
    num_units: 1
relations:
- - kubernetes-master:certificates
  - vault:certificates
- - etcd:certificates
  - vault:certificates
- - kubernetes-worker:certificates
  - vault:certificates
- - kubeapi-load-balancer:certificates
  - vault:certificates
- - vault:shared-db
  - percona-cluster:shared-db

Save this to a file named k8s-vault.yaml and deploy with:

juju deploy charmed-kubernetes --overlay ./k8s-vault.yaml
juju remove-application easyrsa

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 guide 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  # this will give you 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  # this will give you a token to auth the charm
exit
juju run-action vault/0 authorize-charm token={charm token}

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.

Transitioning an existing cluster from EasyRSA to Vault

An existing Charmed Kubernetes deployment which is using EasyRSA can be transitioned to use Vault as a CA.

Follow the same steps as outlined above, and redeploy the same base bundle which was initially deployed on top of the existing deployment, adding the Vault overlay (download).

Note: Using an unpinned bundle revision may result in the cluster charms being upgraded. To avoid this, specify the exact bundle revision you deployed originally, or use `juju export-bundle` to create a custom bundle based on exactly what is currently deployed.

For example, for a 1.15 release:

juju deploy charmed-kubernetes-139 --overlay ./k8s-vault.yaml

Then follow the steps to unseal Vault. This will transition all of the components of the cluster to the new CA and certificates. This will not cause any disruption to running workloads, but you will be unable to issue cluster commands with kubectl for a brief period.

After the transition, you must remove EasyRSA to prevent it from conflicting with Vault:

juju remove-application easyrsa

You will need to re-download the kubectl config file, since it contains the certificate info for connecting to the cluster:

juju scp kubernetes-master/0:config ~/.kube/config

Using Vault as an intermediary CA

If you don't wish Vault to act as a self-signed root CA, you can remove the auto-generate-root-ca-cert: true option from the overlay and follow these instructions to generate a Certificate Signing Request (CSR), have it signed by a trusted root CA, and upload it back to Vault.

Using Vault in Auto-Unseal mode

The Vault charm supports the ability to store and manage the unseal keys and root token using Juju leadership data. Note that this means that the unseal keys can be accessed at any time from the machine that Vault is running on, significantly reducing the security of Vault, particularly with respect to serving as a secure secrets store. If you are comfortable with this reduction in security and don't want to have to deal with the manual steps involved in managing the unseal keys and root token, you can add the following to the options section of vault in the overlay above:

    totally-unsecure-auto-unlock: true

Using Vault with HA

To enable HA for Vault, you will need to first bring up the deployment with Vault in non-HA mode using the instructions above, waiting for everything to settle, and then transitioning Vault to HA mode. This is necessary because Vault requires etcd to be running to enter HA mode, but etcd requires PKI certificates to get up and running, leading to a chicken-and-egg conflict.

Once the deployment is up and settled according to the instructions above, with Vault unsealed and everything functioning, you can then transition Vault to HA mode with the following commands:

juju add-relation vault:etcd etcd
juju add-unit vault

Once the second unit of Vault is up, you will also need to unseal it using the same instructions above with any three of the five unseal keys and the root token you generated previously.