Vault

The Vault Issuer represents the certificate authority Vault - a multi-purpose secret store that can be used to sign certificates for your Public Key Infrastructure (PKI). Vault is an external project to cert-manager and as such, this guide will assume it has been configured and deployed correctly, ready for signing. You can read more on how to configure Vault as a certificate authority here.

This Issuer type is typically used when Vault is already being used within your infrastructure, or you would like to make use of it’s feature set where the CA issuer alone cannot provide.

Deployment

All Vault issuers share common configuration for requesting certificates, namely the server, path, and CA bundle:

• Server is the URL whereby Vault is reachable.
• Path is the Vault path that will be used for signing. Note that the path must use the sign endpoint.
• CA bundle denotes an optional field containing a base64 encoded string of the Certificate Authority to trust the Vault connection. This is typically always required when using an https URL.

Below is an example of a configuration to connect a Vault server.

Warning: This configuration is incomplete as no authentication methods have been added.

apiVersion: cert-manager.io/v1alpha2
kind: Issuer
metadata:
  name: vault-issuer
  namespace: sandbox
spec:
  vault:
    path: pki_int/sign/example-dot-com
    server: https://vault.local
    caBundle: <base64 encoded CA Bundle PEM file>
    auth:
      ...

Authenticating

In order to request signing of certificates by Vault, the issuer must be able to properly authenticate against it. cert-manger provides multiple approaches to authenticating to Vault which are detailed below.

Authenticating via an AppRole

An AppRole is a method of authenticating to Vault through use of it’s internal role policy system. This authentication method requires that the issuer has possession of the SecretID secret key, the RoleID of the role to assume, and the app role path. Firstly, the secret ID key must be stored within a Kubernetes Secret that resides in the same namespace as the Issuer, or otherwise inside the Cluster Resource Namespace in the case of a ClusterIssuer.

apiVersion: v1
kind: Secret
type: Opaque
metadata:
  name: cert-manager-vault-approle
  namespace: sandbox
data:
  secretId: "MDI..."

Once the Secret has been created, the Issuer is ready to be deployed which references this Secret, as well as the data key of the field that stores the secret ID.

apiVersion: cert-manager.io/v1alpha2
kind: Issuer
metadata:
  name: vault-issuer
  namespace: sandbox
spec:
  vault:
    path: pki_int/sign/example-dot-com
    server: https://vault.local
    caBundle: <base64 encoded caBundle PEM file>
    auth:
      appRole:
        path: approle
        roleId: "291b9d21-8ff5-..."
        secretRef:
          name: cert-manager-vault-approle
          key: secretId

Authenticating with a Token

This method of authentication uses a token string that has been generated from one of the many authentication backends that Vault supports. These tokens have an expiry and so need to be periodically refreshed. You can read more on Vault tokens here.

Note: cert-manager does not refresh these token automatically and so another process must be put in place to do this.

Firstly, the token is be stored inside a Kubernetes Secret inside the same namespace as the Issuer or otherwise in the Cluster Resource Namespace in the case of using a ClusterIssuer.

apiVersion: v1
kind: Secret
type: Opaque
metadata:
  name: cert-manager-vault-token
  namespace: sandbox
data:
  token: "MjI..."

Once submitted, the Vault issuer is able to be created using token authentication by referencing this Secret along with the key of the field the token data is stored at.

apiVersion: cert-manager.io/v1alpha2
kind: Issuer
metadata:
  name: vault-issuer
  namespace: sandbox
spec:
  vault:
    path: pki_int/sign/example-dot-com
    server: https://vault.local
    caBundle: <base64 encoded caBundle PEM file>
    auth:
      tokenSecretRef:
          name: cert-manager-vault-token
          key: token

Authenticating with Kubernetes Service Accounts

Vault can be configured so that applications can authenticate using Kubernetes Service Account Tokens. You find documentation on how to configure Vault to authenticate using Service Account Tokens here.

For the Vault issuer to use this authentication, cert-manager must get access to the token that is stored in a Kubernetes Secret. Kubernetes Service Account Tokens are already stored in Secret resources so this does not need to be created manually however, you must ensure that it is present in the same namespace as the Issuer, or otherwise in the Cluster Resource Namespace in the case of using a ClusterIssuer.

This authentication method also expects a role field which is the Vault role that the Service Account is to assume, as well as an optional path field which is the authentication mount path, defaulting to kubernetes.

The following example will be making use of the Service Account my-service-account. The secret data field key will be token if the Secret has been created by Kubernetes.

apiVersion: cert-manager.io/v1alpha2
kind: Issuer
metadata:
  name: vault-issuer
  namespace: sandbox
spec:
  vault:
    path: pki_int/sign/example-dot-com
    server: https://vault.local
    caBundle: <base64 encoded caBundle PEM file>
    auth:
      kubernetes:
        role: my-app-1
        mountPath: /v1/auth/kubernetes
        secretRef:
          name: my-service-account-token-hvwsb
          key: token

Verifying the issuer Deployment

Once the Vault issuer has been deployed, it will be marked as ready if the configuration is valid. Replace issuers here with clusterissuers if that is what has been deployed.

$ kubectl get issuers vault-issuer -n sandbox -o wide
NAME          READY   STATUS          AGE
vault-issuer  True    Vault verified  2m

Certificates are now ready to be requested by using the Vault issuer named vault-issuer within the sandbox namespace.