Vault CSI Provider

The Vault CSI Provider allows pods to consume Vault secrets using CSI Secrets Store volumes.

Overview

At a high level, the CSI Secrets Store driver allows users to create SecretProviderClass objects. This object defines which secret provider to use and what secrets to retrieve. When pods requesting CSI volumes are created, the CSI Secrets Store driver will send the request to the Vault CSI Provider if the provider is vault. The Vault CSI Provider will then use Secret Provider Class specified and the pod's service account to retrieve the secrets from Vault, and mount them into the pod's CSI volume.

The secret is retrieved from Vault and populated to the CSI secrets store volume during the ContainerCreation phase. This means that pods will be blocked from starting until the secrets have been read from Vault and written to the volume.

Features

The following features are supported by the Vault CSI Provider:

• All Vault secret engines supported.
• Authentication using the requesting pod's service account.
• TLS/mTLS communications with Vault.
• Rendering Vault secrets to files.
• Syncing secrets to Kubernetes secrets to be used as environment variables.
• Installation via Vault Helm

Authenticating with Vault

The primary method of authentication with Vault when using the Vault CSI Provider is the service account attached to the pod. At this time no other authentication methods are supported.

For Kubernetes authentication, the service account must be bound to a Vault role and a policy granting access to the secrets desired.

A service account must be present to use the Vault CSI Provider with the Kubernetes authentication method. It is not recommended to bind Vault roles to the default service account provided to pods if no service account is defined.

Setting issuer for Kubernetes authentication

If running Vault prior to version 1.9, you will likely need to set issuer when configuring Kubernetes authentication for the Vault CSI Provider. Vault CSI Provider does not use the default token associated with service accounts. Instead, it creates a token with a short TTL whose lifetime is also bound to the lifetime of the requesting pod. A key difference between default tokens and ephemeral tokens is the JWT issuer. Default tokens use kubernetes/serviceaccount, which is the default value that Kubernetes auth will try to validate. However, ephemeral tokens use the value of kube-apiserver's --service-account-issuer flag as the issuer, which is normally a URL instead. See the Kubernetes auth docs for ways to check the issuer using the Kubernetes API.

Importantly, this means most common configurations of Vault Agent Injector and Vault CSI Provider cannot share the same Kubernetes auth mount. Vault Agent sidecars will most commonly be configured to authenticate using a long-lived default service account token, with an issuer different to the tokens Vault CSI Provider will create. But one Kubernetes auth mount can only be configured to validate a single issuer value.

Secret Provider Class Example

The following is an example of a Secret Provider Class using the vault provider:

---
apiVersion: secrets-store.csi.x-k8s.io/v1alpha1
kind: SecretProviderClass
metadata:
  name: vault-db-creds
spec:
  # Vault CSI Provider
  provider: vault
  parameters:
    # Vault role name to use during login
    roleName: 'app'
    # Vault's hostname
    vaultAddress: 'https://vault:8200'
    # TLS CA certification for validation
    vaultCACertPath: '/vault/tls/ca.crt'
    objects: |
      - objectName: "dbUsername"
        secretPath: "database/creds/db-app"
        secretKey: "username"
      - objectName: "dbPassword"
        secretPath: "database/creds/db-app"
        secretKey: "password"
    # "objectName" is an alias used within the SecretProviderClass to reference
    # that specific secret. This will also be the filename containing the secret.
    # "secretPath" is the path in Vault where the secret should be retrieved.
    # "secretKey" is the key within the Vault secret response to extract a value from.

Using Secret Provider Classes

An application pod uses the example Secret Provider Class above by mounting it as a CSI volume:

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: app
  labels:
    app: demo
spec:
  selector:
    matchLabels:
      app: demo
  replicas: 1
  template:
    spec:
      serviceAccountName: app
      containers:
        - name: app
          image: my-app:1.0.0
          volumeMounts:
            - name: 'vault-db-creds'
              mountPath: '/mnt/secrets-store'
              readOnly: true
      volumes:
        - name: vault-db-creds
          csi:
            driver: 'secrets-store.csi.k8s.io'
            readOnly: true
            volumeAttributes:
              secretProviderClass: 'vault-db-creds'

In this example volumes.csi is created on the application deployment and references the Secret Provider Class named vault-db-creds.

Tutorial

Refer to the Vault CSI Provider tutorial to learn how to set up Vault and its depedencies with a Helm chart.