Mount PKI(certificates) 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.
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 PKI Secret Engine
We will use the Vault CLI throughout the tutorial to enable and configure the PKI secret engine.
Don’t have Vault CLI? Download and configure it as described here
To use secret from PKI secret engine, you have to perform the following steps.
Enable PKI Secret Engine
To enable PKI secret engine run the following command.
$ vault secrets enable pki
Success! Enabled the pki secrets engine at: pki/
Increase the TTL by tuning the secrets engine. The default value of 30 days may be too short, so increase it to 1 year:
$ vault secrets tune -max-lease-ttl=8760h pki
Success! Tuned the secrets engine at: pki/
Configure CA Certificate and Private Key
Configure a CA certificate and private key. Vault can accept an existing key pair, or it can generate its own self-signed root.
$ vault write pki/root/generate/internal \
common_name=my-website.com \
ttl=8760h
Key Value
--- -----
certificate -----BEGIN CERTIFICATE-----
MIIDPjCCAiagAwIBAgIUEDmnAmC0siISlrezD3/CeUXTSfswDQYJKoZIhvcNAQEL
... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ...
CsFVu+vfMM9XEMYeKHRWAq9onJFyGuwKGhF0/7RbZ3EunTj6Zph+UMucGoL4xfXj
ITltdU1N4JPvihQq+8Omryay
-----END CERTIFICATE-----
expiration 1606200496
issuing_ca -----BEGIN CERTIFICATE-----
MIIDPjCCAiagAwIBAgIUEDmnAmC0siISlrezD3/CeUXTSfswDQYJKoZIhvcNAQEL
... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ...
CsFVu+vfMM9XEMYeKHRWAq9onJFyGuwKGhF0/7RbZ3EunTj6Zph+UMucGoL4xfXj
ITltdU1N4JPvihQq+8Omryay
-----END CERTIFICATE-----
serial_number 10:39:a7:02:60:b4:b2:22:12:96:b7:b3:0f:7f:c2:79:45:d3:49:fb
Configure a PKI Role
We need to configure a role that maps a name in vault to a procedure for generating certificate. When users of machines generate credentials, they are generated agains this role:
$ vault write pki/roles/example-dot-com \
allowed_domains=my-website.com \
allow_subdomains=true \
max_ttl=72h
Success! Data written to: pki/roles/example-dot-com
Create Service Account for Pod
Let’s create the service account test-user-account which will be used in VaultPolicyBinding.
apiVersion: v1
kind: ServiceAccount
metadata:
name: test-user-account
namespace: demo
$ kubectl apply -f docs/examples/guides/secret-engines/pki/serviceaccount.yaml
serviceaccount/test-user-account created
$ kubectl get serviceaccount -n demo
NAME SECRETS AGE
test-user-account 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.pki-se-role.
apiVersion: policy.kubevault.com/v1alpha1
kind: VaultPolicy
metadata:
name: pki-se-policy
namespace: demo
spec:
vaultRef:
name: vault
policyDocument: |
path "pki/issue/*" {
capabilities = ["update"]
}
---
apiVersion: policy.kubevault.com/v1alpha1
kind: VaultPolicyBinding
metadata:
name: pki-se-role
namespace: demo
spec:
vaultRef:
name: vault
policies:
- ref: pki-se-policy
subjectRef:
kubernetes:
serviceAccountNames:
- "test-user-account"
serviceAccountNamespaces:
- "demo"
Let’s create VaultPolicy and VaultPolicyBinding:
$ kubectl apply -f docs/examples/guides/secret-engines/pki/policy.yaml
vaultpolicy.policy.kubevault.com/pki-se-policy created
$ kubectl apply -f docs/examples/guides/secret-engines/pki/policybinding.yaml
vaultpolicybinding.policy.kubevault.com/pki-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
pki-se-policy Success 8s
$ kubectl get vaultpolicybinding -n demo
NAME STATUS AGE
pki-se-role Success 10s
Mount Certificates 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-db-provider
namespace: demo
spec:
provider: vault
parameters:
vaultAddress: "http://vault.demo:8200"
roleName: "k8s.-.demo.pki-se-role"
objects: |
- objectName: "certificate"
secretPath: "pki/issue/example-dot-com"
secretKey: "certificate"
secretArgs:
common_name: "www.my-website.com"
ttl: 24h
method: "POST"
- objectName: "issuing_ca"
secretPath: "pki/issue/example-dot-com"
secretKey: "issuing_ca"
secretArgs:
common_name: "www.my-website.com"
ttl: 24h
method: "POST"
- objectName: "private_key"
secretPath: "pki/issue/example-dot-com"
secretKey: "private_key"
secretArgs:
common_name: "www.my-website.com"
ttl: 24h
method: "POST"
- objectName: "private_key_type"
secretPath: "pki/issue/example-dot-com"
secretKey: "private_key_type"
secretArgs:
common_name: "www.my-website.com"
ttl: 24h
method: "POST"
$ kubectl apply -f docs/examples/guides/secret-engines/pki/secretproviderclass.yaml
secretproviderclass.secrets-store.csi.x-k8s.io/vault-db-provider created
Here, you can also pass the following parameters optionally to issue the certificate
common_name(string:) – Specifies the requested CN for the certificate. If the CN is allowed by role policy, it will be issued. alt_names(string: “”) – Specifies requested Subject Alternative Names, in a comma-delimited list. These can be host names or email addresses; they will be parsed into their respective fields. If any requested names do not match role policy, the entire request will be denied.ip_sans(string: “”) – Specifies requested IP Subject Alternative Names, in a comma-delimited list. Only valid if the role allows IP SANs (which is the default).uri_sans(string: “”) – Specifies the requested URI Subject Alternative Names, in a comma-delimited list.other_sans(string: “”) – Specifies custom OID/UTF8-string SANs. These must match values specified on the role in allowed_other_sans (globbing allowed). The format is the same as OpenSSL:; : where the only current valid type is UTF8. This can be a comma-delimited list or a JSON string slice. ttl(string: “”) – Specifies requested Time To Live. Cannot be greater than the role’s max_ttl value. If not provided, the role’s ttl value will be used. Note that the role values default to system values if not explicitly set.format(string: “”) – Specifies the format for returned data. Can be pem, der, or pem_bundle; defaults to pem. If der, the output is base64 encoded. If pem_bundle, the certificate field will contain the private key and certificate, concatenated; if the issuing CA is not a Vault-derived self-signed root, this will be included as well.private_key_format(string: “”) – Specifies the format for marshaling the private key. Defaults to der which will return either base64-encoded DER or PEM-encoded DER, depending on the value of format. The other option is pkcs8 which will return the key marshalled as PEM-encoded PKCS8.exclude_cn_from_sans(bool: false) – If true, the given common_name will not be included in DNS or Email Subject Alternate Names (as appropriate). Useful if the CN is not a hostname or email address, but is instead some human-readable identifier.
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 PKI 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: demo-app
namespace: demo
spec:
serviceAccountName: test-user-account
containers:
- image: jweissig/app:0.0.1
name: demo-app
imagePullPolicy: Always
volumeMounts:
- name: secrets-store-inline
mountPath: "/secrets-store/pki-assets"
readOnly: true
volumes:
- name: secrets-store-inline
csi:
driver: secrets-store.csi.k8s.io
readOnly: true
volumeAttributes:
secretProviderClass: "vault-db-provider"
$ kubectl apply -f docs/examples/guides/secret-engines/pki/pod.yaml
pod/demo-app created
Test & Verify
Check if the Pod is running successfully, by running:
$ kubectl get pods -n demo
NAME READY STATUS RESTARTS AGE
demo-app 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 test pod/demo-app -- /bin/sh
/ # ls /secrets-store/pki-assets
certificate issuing_ca private_key private_key_type
/ # cat /secrets-store/pki-assets/certificate
-----BEGIN CERTIFICATE-----
MIIDVjCCAj6gAwIBAgIUNjTBC3qR7Zaj0XrzUc3QEbE+EhgwDQYJKoZIhvcNAQEL
BQAwGTEXMBUGA1UEAxMObXktd2Vic2l0ZS5jb20wHhcNMTkxMjEzMTExNDIwWhcN
..... .... .... .... .... .... .... .... .... .... .... .... ...
bo901cITjNyCTbAF2401pYFZ4rSlxhcuAvc7c27uqvKEh2/ctMGRkvPVygbPdvB8
LfCskfX0sk8PQiEznlmYlChK3KNsEp+xSCyjU+pDEw8AcDXwE6vVFft/fRX0oiHH
KIzTZ7R/QKUkLisloMUHStINISAehglLZTJjo79jB7GN66wyqP+E8iRLEYFAAsb0
aZ5wuSTYEpqOuP6G1tOdhiE7iptFu9Wg9dKtmXkZnc0iTBL60xMUUapH
-----END CERTIFICATE-----
Cleaning up
To clean up the Kubernetes resources created by this tutorial, run:
$ kubectl delete ns demo
namespace "demo" deleted