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Use Google Secret Manager in a GKE cluster

Use Google Secret Manager in a GKE cluster

February 26, 2023

There are an awesome article about the options to use the Google Secret Manager and their pros and cons. In this article, use Secrets Store CSI Driver by following this page.

Set up a secrets store CSI driver

First, install the secrets-store-csi-driver in kube-system namespace

helm repo add secrets-store-csi-driver https://kubernetes-sigs.github.io/secrets-store-csi-driver/charts
helm install csi-secrets-store secrets-store-csi-driver/secrets-store-csi-driver --namespace kube-system

Next, install the GCP provider for the secrets store CSI driver from this repository. Unfortunately, there is no helm chart as the time of this post is written, according to this GitHub issue.

Just download deploy/provider-gcp-plugin.yaml and apply it to the cluster.

kubectl apply -f deploy/provider-gcp-plugin.yaml

Use the secrets from a kubernetes

Just follow the usage described in the secrets-store-csi-driver-provider-gcp repository.

These are overview, though I changed names of namespaces:

  • The secret name is secrets_store_csi_driver_test
  • The pod uses a secrets store CSI driver needs a permission to access Google Secret Manager, like with a workload identity
  • GCP Service account name is gke-secrets-store-csi-test with the role roles/secretmanager.secretAccessor
  • The pod is in test-secrets-store-csi namespace and the service account name is default

Then I create following k8s resources.

apiVersion: secrets-store.csi.x-k8s.io/v1
kind: SecretProviderClass
metadata:
  name: app-secrets
spec:
  provider: gcp
  parameters:
    secrets: |
      - resourceName: "projects/$PROJECT_ID/secrets/secrets_store_csi_driver_test/versions/latest"
        path: "good1.txt"
      - resourceName: "projects/$PROJECT_ID/secrets/secrets_store_csi_driver_test/versions/latest"
        path: "good2.txt"
apiVersion: v1
kind: ServiceAccount
metadata:
  name: mypodserviceaccount
  namespace: default
  annotations:
    iam.gke.io/gcp-service-account: gke-workload@$PROJECT_ID.iam.gserviceaccount.com
---
apiVersion: v1
kind: Pod
metadata:
  name: mypod
  namespace: default
spec:
  serviceAccountName: mypodserviceaccount
  containers:
  - image: gcr.io/google.com/cloudsdktool/cloud-sdk:slim
    imagePullPolicy: IfNotPresent
    name: mypod
    resources:
      requests:
        cpu: 100m
    stdin: true
    stdinOnce: true
    terminationMessagePath: /dev/termination-log
    terminationMessagePolicy: File
    tty: true
    volumeMounts:
      - mountPath: "/var/secrets"
        name: mysecret
  volumes:
  - name: mysecret
    csi:
      driver: secrets-store.csi.k8s.io
      readOnly: true
      volumeAttributes:
        secretProviderClass: "app-secrets"

After I deployed k8s resources and configure GCP resources, I was able to see the secrets are mounted:

[personal|test-secrets-store-csi] > kubectl exec -it mypod /bin/bash
root@mypod:/# ls /var/secrets
good1.txt  good2.txt
root@mypod:/# cat /var/secrets/good1.txt
foo
root@mypod:/# cat /var/secrets/good2.txt
foo

Sync as Kubernetes Secret

This is an alpha feature, but it’s possible to sync and generate the data as a k8s secret, described in this page. Note that the volume mount is required for the Sync With Kubernetes Secrets

To use this feature, at first, enable the feature on the helm chart.

syncSecret:
  enabled: true

Then change k8s resources like next. I checked how to write the configuration for secret objects from the test code of the provider.

@@ -11,6 +11,12 @@ spec:
         path: "good1.txt"
       - resourceName: "projects/$PROJECT_ID/secrets/secrets_store_csi_driver_test/versions/latest"
         path: "good2.txt"
+  secretObjects:
+  - data:
+    - key: test-secret-contents
+      objectName: "good1.txt"
+    type: Opaque
+    secretName: test-synced-secret
 ---
 apiVersion: v1
 kind: ServiceAccount
@@ -31,6 +37,12 @@ spec:
   - image: gcr.io/google.com/cloudsdktool/cloud-sdk:slim
     imagePullPolicy: IfNotPresent
     name: mypod
+    env:
+    - name: SECRET_CONTENTS
+      valueFrom:
+        secretKeyRef:
+            name: test-synced-secret
+            key: test-secret-contents
     resources:
       requests:
         cpu: 100m

If you don’t mount it on a volume mount, you’ll get an error like this

status:
  conditions:
    containerStatuses:
    - waiting:
        message: secret "test-synced-secret" not found
        reason: CreateContainerConfigError

When you succeed to deploy, you can see the secrets like

[personal|test-secrets-store-csi] > kubectl get secrets
NAME                  TYPE                                  DATA   AGE
default-token-qbwgz   kubernetes.io/service-account-token   3      10d
test-synced-secret    Opaque                                1      1s
[personal|test-secrets-store-csi] > kubectl view-secret test-synced-secret
Choosing key: test-secret-contents
foo
[personal|test-secrets-store-csi] > kubectl exec -it mypod /bin/bash
kubectl exec [POD] [COMMAND] is DEPRECATED and will be removed in a future version. Use kubectl exec [POD] -- [COMMAND] instead.
root@mypod2:/# echo $SECRET_CONTENTS
foo
root@mypod2:/# exit
exit

Additional features

There are a a few features that are still alpha:

  • Auto rotation
    • The secrets mounted on a pod will be automatically updated, but this doesn’t support rotating secrets on an application side. Application has to implement a way to update secrets by detecting the updates
    • SecretProviderClassPodStatus resource stores the binding of a secret and a pod, and it also contains the version of the secret.
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