Mount Key/Value Secrets using CSI Driver
Kubernetes Secrets Store CSI Driver
Secrets Store CSI driver for Kubernetes secrets - Integrates secrets stores with Kubernetes via a Container Storage Interface (CSI) volume.
The Secrets Store CSI driver secrets-store.csi.k8s.io allows Kubernetes to mount multiple secrets, keys, and certs stored in enterprise-grade external secrets stores into their pods as a volume. Once the Volume is attached, the data in it is mounted into the container’s file system.
When the Pod is created through the K8s API, it’s scheduled on to a node. The kubelet process on the node looks at the pod spec & see if there’s any volumeMount request. The kubelet issues an RPC to the CSI driver to mount the volume. The CSI driver creates & mounts tmpfs into the pod. Then the CSI driver issues a request to the Provider. The provider talks to the external secrets store to fetch the secrets & write them to the pod volume as files. At this point, volume is successfully mounted & the pod starts running.
You can read more about the Kubernetes Secrets Store CSI Driver here.
Consuming Secrets
At first, you need to have a Kubernetes 1.16 or later cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using kind. To check the version of your cluster, run:
$ kubectl version --short
Client Version: v1.21.2
Server Version: v1.21.1
Before you begin:
- Install KubeVault operator in your cluster from here.
- Install Secrets Store CSI driver for Kubernetes secrets in your cluster from here.
- Install Vault Specific CSI provider from here
To keep things isolated, we are going to use a separate namespace called demo throughout this tutorial.
$ kubectl create ns demo
namespace/demo created
Note: YAML files used in this tutorial stored in examples folder in GitHub repository KubeVault/docs
Vault Server
If you don’t have a Vault Server, you can deploy it by using the KubeVault operator.
The KubeVault operator can manage policies and secret engines of Vault servers which are not provisioned by the KubeVault operator. You need to configure both the Vault server and the cluster so that the KubeVault operator can communicate with your Vault server.
Now, we have the AppBinding that contains connection and authentication information about the Vault server. And we also have the service account that the Vault server can authenticate.
$ kubectl get appbinding -n demo
NAME AGE
vault 50m
$ kubectl get appbinding -n demo vault -o yaml
apiVersion: appcatalog.appscode.com/v1alpha1
kind: AppBinding
metadata:
creationTimestamp: "2021-08-16T08:23:38Z"
generation: 1
labels:
app.kubernetes.io/instance: vault
app.kubernetes.io/managed-by: kubevault.com
app.kubernetes.io/name: vaultservers.kubevault.com
name: vault
namespace: demo
ownerReferences:
- apiVersion: kubevault.com/v1alpha1
blockOwnerDeletion: true
controller: true
kind: VaultServer
name: vault
uid: 6b405147-93da-41ff-aad3-29ae9f415d0a
resourceVersion: "602898"
uid: b54873fd-0f34-42f7-bdf3-4e667edb4659
spec:
clientConfig:
service:
name: vault
port: 8200
scheme: http
parameters:
apiVersion: config.kubevault.com/v1alpha1
kind: VaultServerConfiguration
kubernetes:
serviceAccountName: vault
tokenReviewerServiceAccountName: vault-k8s-token-reviewer
usePodServiceAccountForCSIDriver: true
path: kubernetes
vaultRole: vault-policy-controller
Enable and Configure KV Secret Engine
We will use the Vault CLI throughout the tutorial to enable and configure the KV secret engine.
Don’t have Vault CLI? Download and configure it as described here
Enable KV Secret Engine
Enable the KV secret engine:
$ vault secrets enable -path=secret kv
Success! Enabled the kv secrets engine at: secret/
Write KV Secret
Write arbitrary key-value pairs:
$ vault kv put secret/db-pass password="db-secret-password"
Success! Data written to: secret/db-pass
Read KV Secret
Read a specific key-value pair:
$ vault kv get secret/db-pass
====== Data ======
Key Value
--- -----
password db-secret-password
Let’s say pod’s service account name is pod-sa located in demo namespace. We need to create a VaultPolicy and a VaultPolicyBinding so that the pod has access to read secrets from the Vault server.
Create Service Account for Pod
Let’s create the service account pod-sa which will be used in VaultPolicyBinding.
apiVersion: v1
kind: ServiceAccount
metadata:
name: pod-sa
namespace: demo
$ kubectl apply -f docs/examples/guides/secret-engines/kv/serviceaccount.yaml
serviceaccount/pod-sa created
$ kubectl get serviceaccount -n demo
NAME SECRETS AGE
pod-sa 1 4h10m
Create VaultPolicy and VaultPolicyBinding for Pod’s Service Account
When a VaultPolicyBinding object is created, the KubeVault operator create an auth role in the Vault server. The role name is generated by the following naming format: k8s.(clusterName or -).namespace.name. Here, it is k8s.-.demo.kv-se-role.
apiVersion: policy.kubevault.com/v1alpha1
kind: VaultPolicy
metadata:
name: kv-se-policy
namespace: demo
spec:
vaultRef:
name: vault
policyDocument: |
path "secret/db-pass" {
capabilities = ["read"]
}
---
apiVersion: policy.kubevault.com/v1alpha1
kind: VaultPolicyBinding
metadata:
name: kv-se-role
namespace: demo
spec:
vaultRef:
name: vault
policies:
- ref: kv-se-policy
subjectRef:
kubernetes:
serviceAccountNames:
- "pod-sa"
serviceAccountNamespaces:
- "trial"
Let’s create VaultPolicy and VaultPolicyBinding:
$ kubectl apply -f docs/examples/guides/secret-engines/kv/policy.yaml
vaultpolicy.policy.kubevault.com/kv-se-policy created
$ kubectl apply -f docs/examples/guides/secret-engines/kv/policybinding.yaml
vaultpolicybinding.policy.kubevault.com/kv-se-role created
Check if the VaultPolicy and the VaultPolicyBinding are successfully registered to the Vault server:
$ kubectl get vaultpolicy -n demo
NAME STATUS AGE
kv-se-policy Success 8s
$ kubectl get vaultpolicybinding -n demo
NAME STATUS AGE
kv-se-role Success 10s
Mount secrets into a Kubernetes pod
So, we can create SecretProviderClass now. You can read more about SecretProviderClass here.
Create SecretProviderClass
Create SecretProviderClass object with the following content:
apiVersion: secrets-store.csi.x-k8s.io/v1alpha1
kind: SecretProviderClass
metadata:
name: vault-database
namespace: demo
spec:
provider: vault
parameters:
vaultAddress: "http://vault.demo:8200"
roleName: "k8s.-.demo.kv-se-role"
objects: |
- objectName: "db-password"
secretPath: "secret/db-pass"
secretKey: "password"
$ kubectl apply -f docs/examples/guides/secret-engines/kv/secretproviderclass.yaml
secretproviderclass.secrets-store.csi.x-k8s.io/vault-database created
NOTE: The SecretProviderClass needs to be created in the same namespace as the pod.
Create Pod
Now we can create a Pod to consume the KV secrets. When the Pod is created, the Provider fetches the secret and writes them to Pod’s volume as files. At this point, the volume is successfully mounted and the Pod starts running.
apiVersion: v1
kind: Pod
metadata:
name: mypod
namespace: demo
spec:
serviceAccountName: pod-sa
containers:
- image: jweissig/app:0.0.1
name: test-app
volumeMounts:
- name: secrets-store-inline
mountPath: "/secrets-store/test"
readOnly: true
volumes:
- name: secrets-store-inline
csi:
driver: secrets-store.csi.k8s.io
readOnly: true
volumeAttributes:
secretProviderClass: "vault-database"
$ kubectl apply -f docs/examples/guides/secret-engines/kv/pod.yaml
pod/mypod created
Test & Verify
Check if the Pod is running successfully, by running:
$ kubectl get pods -n demo
NAME READY STATUS RESTARTS AGE
mypod 1/1 Running 0 11s
Verify Secret
If the Pod is running successfully, then check inside the app container by running
$ kubectl exec -it -n demo mypod sh
/ # ls /secrets-store/test
db-password
/ # cat /secrets-store/test/db-password
db-secret-password
/ # exit
So, we can see that the secret db-password is mounted into the pod, where the secret key is mounted as file and value is the content of that file.
Cleaning up
To clean up the Kubernetes resources created by this tutorial, run:
$ kubectl delete ns demo
namespace "demo" deleted