This is an experimental project and is not production ready. More details are available here.
Kubernetes application pods that rely on Vault to manage their secrets can retrieve them directly via network requests or maintained on a mounted file system through the Vault Injector service via annotations or attached as ephemeral volumes. This approach of employing ephemeral volumes to store secrets is a feature of the Secrets Store extension to the Kubernetes Container Storage Interface (CSI) driver.
In this tutorial, you will setup Vault and its dependencies with a Helm chart. Then enable and configure the secrets store CSI driver to create a volume that contains a secret that you will mount to an application pod.
»Prerequisites
This tutorial requires the Kubernetes command-line interface (CLI) and the Helm CLI installed, Minikube, and additional configuration to bring it all together.
Online tutorial: An interactive tutorial is also available if you do not wish to install the following resources. Click the Show Terminal button to start.
This tutorial was last tested 20 Jun 2020 on macOS 10.15.5 using this configuration.
Docker version.
$ docker version
Client: Docker Engine - Community
Version: 19.03.8
# ...
Minikube version.
$ minikube version
minikube version: v1.11.0
commit: 57e2f55f47effe9ce396cea42a1e0eb4f611ebbd
Helm version.
$ helm version
version.BuildInfo{Version:"v3.2.1", GitCommit:"fe51cd1e31e6a202cba7dead9552a6d418ded79a", GitTreeState:"clean", GoVersion:"go1.13.10"}
These are recommended software versions and the output displayed may vary depending on your environment and the software versions you use.
First, follow the directions to install Minikube, including VirtualBox or similar.
Next, install kubectl CLI and helm CLI.
Install kubectl with Homebrew.
$ brew install kubernetes-cli
Install helm with Homebrew.
$ brew install helm
»Start Minikube
Minikube is a CLI tool that provisions and manages the lifecycle of single-node Kubernetes clusters. These clusters are run locally inside Virtual Machines (VM).
Start a Kubernetes cluster.
$ minikube start
😄 minikube v1.11.0 on Darwin 10.15.5
✨ Automatically selected the hyperkit driver
👍 Starting control plane node minikube in cluster minikube
🔥 Creating hyperkit VM (CPUs=2, Memory=4000MB, Disk=20000MB) ...
🐳 Preparing Kubernetes v1.18.3 on Docker 19.03.8 ...
🔎 Verifying Kubernetes components...
🌟 Enabled addons: default-storageclass, storage-provisioner
🏄 Done! kubectl is now configured to use "minikube"
Verify the status of the Minikube cluster.
$ minikube status
minikube
type: Control Plane
host: Running
kubelet: Running
apiserver: Running
kubeconfig: Configured
Additional waiting: Even if this last command completed successfully, you may have to wait for Minikube to be available. If an error is displayed, try again after a few minutes.
The host, kubelet, apiserver report that they are running. The kubectl, a
command line interface (CLI) for running commands against Kubernetes cluster, is
also configured to communicate with this recently started cluster.
»Install the Vault Helm chart
Vault manages the secrets that are written to these mountable volumes. To provide these secrets a single Vault server is required. For this demonstration Vault can be run in development mode to automatically handle initialization, unsealing, and setup of a KV secrets engine.
Add the HashiCorp Helm repository.
$ helm repo add hashicorp https://helm.releases.hashicorp.com
"hashicorp" has been added to your repositories
Install the latest version of the Vault Helm chart running in development mode with the injector service disabled.
$ helm install vault hashicorp/vault \
--set "server.dev.enabled=true" \
--set "injector.enabled=false"
NAME: vault
## ...
The Vault server runs in development mode on a single pod
server.dev.enabled=true. By default the Helm chart starts a Vault Agent
Injector pod but that is disabled injector.enabled=false.
Display all the pods within the default namespace.
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
vault-0 1/1 Running 0 87s
Wait until the vault-0 pod is running and ready (1/1).
»Set a secret in Vault
The volume mounted to the pod in the Create a pod with secret
mounted section expects a secret stored at
the path secret/data/db-pass. When Vault is run in development a KV
secret engine is
enabled at the path /secret.
First, start an interactive shell session on the vault-0 pod.
$ kubectl exec -it vault-0 -- /bin/sh
/ $
Your system prompt is replaced with a new prompt / $. Commands issued at this
prompt are executed on the vault-0 container.
Create a secret at the path secret/db-pass with a password.
$ vault kv put secret/db-pass password="db-secret-password"
Key Value
--- -----
created_time 2020-05-30T16:58:54.295890646Z
deletion_time n/a
destroyed false
version 1
Verify that the secret is readable at the path secret/db-pass.
$ vault kv get secret/db-pass
====== Metadata ======
Key Value
--- -----
created_time 2020-05-30T16:58:54.295890646Z
deletion_time n/a
destroyed false
version 1
====== Data ======
Key Value
--- -----
password db-secret-password
Lastly, exit the vault-0 pod.
$ exit
»Configure Kubernetes authentication
Vault provides a Kubernetes authentication method that enables clients to authenticate with a Kubernetes Service Account Token. The Kubernetes resources that access the secret and create the volume authenticate through this method through a role.
First, start an interactive shell session on the vault-0 pod.
$ kubectl exec -it vault-0 -- /bin/sh
/ $
Your system prompt is replaced with a new prompt / $. Commands issued at this
prompt are executed on the vault-0 container.
Enable the Kubernetes authentication method.
$ vault auth enable kubernetes
Success! Enabled kubernetes auth method at: kubernetes/
Configure the Kubernetes authentication method to use the service account token, the location of the Kubernetes host, and its certificate.
$ vault write auth/kubernetes/config \
token_reviewer_jwt="$(cat /var/run/secrets/kubernetes.io/serviceaccount/token)" \
kubernetes_host="https://$KUBERNETES_PORT_443_TCP_ADDR:443" \
kubernetes_ca_cert=@/var/run/secrets/kubernetes.io/serviceaccount/ca.crt
Success! Data written to: auth/kubernetes/config
The token_reviewer_jwt and kubernetes_ca_cert files written to the container
by Kubernetes. The environment variable KUBERNETES_PORT_443_TCP_ADDR
references the internal network address of the Kubernetes host.
For the Kubernetes-Secrets-Store-CSI-Driver to read the secrets requires that it has read permissions of all mounts and access to the secret itself.
Write out the policy named internal-app.
$ vault policy write internal-app - <<EOF
path "sys/mounts" {
capabilities = ["read"]
}
path "secret/data/db-pass" {
capabilities = ["read"]
}
EOF
Success! Uploaded policy: internal-app
Currently the Vault extension of the Kubernetes-Secrets-Store-CSI-Driver only
supports the KV Secrets Engine.
This extension verifies that the requested secret belongs to a supported engine
by reading the mounted secrets engines. The data of
kv-v2 requires that
an additional path element of data is included after its mount path (in this
case, secret/).
Finally, create a Kubernetes authentication role named database that binds
this policy with a Kubernetes service account named secrets-store-csi-driver.
$ vault write auth/kubernetes/role/database \
bound_service_account_names=secrets-store-csi-driver \
bound_service_account_namespaces=default \
policies=internal-app \
ttl=20m
Success! Data written to: auth/kubernetes/role/database
The role connects the Kubernetes service account, secrets-store-csi-driver, in
the namespace, default, with the Vault policy, internal-app. The tokens
returned after authentication are valid for 20 minutes. This Kubernetes service
account name, secrets-store-csi-driver, is created in the Install the secrets
store CSI driver section when the
secrets store CSI driver Helm chart is installed.
Lastly, exit the vault-0 pod.
$ exit
»Install the secrets store CSI driver
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.
Add the Secrets Store CSI driver Helm repository.
$ helm repo add secrets-store-csi-driver https://raw.githubusercontent.com/kubernetes-sigs/secrets-store-csi-driver/master/charts
"secrets-store-csi-driver" has been added to your repositories
Install the latest version of the Kubernetes-Secrets-Store-CSI-Driver.
$ helm install csi secrets-store-csi-driver/secrets-store-csi-driver
NAME: csi
## ...
The csi-secrets-store-csi-driver pod is deployed in the default
namespace.
Get all the pods within the default namespace.
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
csi-secrets-store-csi-driver-6rf2k 3/3 Running 0 29s
vault-0 1/1 Running 0 23m
Wait until the csi-secrets-store-csi-driver pod is running and ready
(3/3).
»Install the provider-vault executable
The Secrets Store CSI driver enables extension through providers. A provider is launched as a Kubernetes DaemonSet alongside of Secrets Store CSI driver DaemonSet.
Create the DaemonSet that installs the provider-vault executable for the
Kubernetes-Secrets-Store-CSI-Driver.
$ cat <<EOF | kubectl apply -f -
apiVersion: apps/v1
kind: DaemonSet
metadata:
labels:
app: csi-secrets-store-provider-vault
name: csi-secrets-store-provider-vault
spec:
updateStrategy:
type: RollingUpdate
selector:
matchLabels:
app: csi-secrets-store-provider-vault
template:
metadata:
labels:
app: csi-secrets-store-provider-vault
spec:
serviceAccount: secrets-store-csi-driver
tolerations:
containers:
- name: provider-vault-installer
image: hashicorp/secrets-store-csi-driver-provider-vault:0.0.6
imagePullPolicy: Always
resources:
requests:
cpu: 50m
memory: 100Mi
limits:
cpu: 50m
memory: 100Mi
env:
- name: TARGET_DIR
value: "/etc/kubernetes/secrets-store-csi-providers"
volumeMounts:
- mountPath: "/etc/kubernetes/secrets-store-csi-providers"
name: providervol
volumes:
- name: providervol
hostPath:
path: "/etc/kubernetes/secrets-store-csi-providers"
nodeSelector:
beta.kubernetes.io/os: linux
EOF
daemonset.apps/csi-secrets-store-provider-vault created
This DaemonSet launches its own provider pod with the name prefixed with
csi-secrets-store-provider-vault and mounts the executable in the existing
csi-secrets-store-csi-driver pod.
Get all the pods within the default namespace.
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
csi-secrets-store-csi-driver-6rf2k 3/3 Running 0 4m40s
csi-secrets-store-provider-vault-qm44g 1/1 Running 0 20s
vault-0 1/1 Running 0 27m
Wait until csi-secrets-store-provider-vault pod is running and ready (1/1).
Verify that the provider-vault executable is present on the secrets-store
container in the secrets-store-csi-driver pod.
$ kubectl exec \
$(kubectl get pod -l app=secrets-store-csi-driver -o jsonpath="{.items[0].metadata.name}") \
-c secrets-store -- \
stat /etc/kubernetes/secrets-store-csi-providers/vault/provider-vault
File: /etc/kubernetes/secrets-store-csi-providers/vault/provider-vault
Size: 8861147 Blocks: 17312 IO Block: 4096 regular file
Device: 10h/16d Inode: 111064 Links: 1
Access: (0755/-rwxr-xr-x) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2020-03-19 20:25:20.726542817 +0000
Modify: 2020-03-19 20:25:20.825490265 +0000
Change: 2020-03-19 20:25:20.825490265 +0000
Birth: -
The executable enables the Vault secrets provider when you define a SecretProviderClass.
»Define a SecretProviderClass resource
The Kubernetes-Secrets-Store-CSI-Driver Helm chart creates a definition for a
SecretProviderClass resource. This resource describes the parameters that are
given to the provider-vault executable. To configure it requires the IP
address of the Vault server, the name of the Vault Kubernetes authentication
role, and the secrets.
Create a SecretProviderClass named vault-database.
$ cat <<EOF | kubectl apply -f -
apiVersion: secrets-store.csi.x-k8s.io/v1alpha1
kind: SecretProviderClass
metadata:
name: vault-database
spec:
provider: vault
parameters:
vaultAddress: "http://vault.default:8200"
roleName: "database"
vaultSkipTLSVerify: "true"
objects: |
array:
- |
objectPath: "v1/secret/db-pass"
objectName: "password"
objectVersion: ""
EOF
secretproviderclass.secrets-store.csi.x-k8s.io/vault-database created
The vault-database SecretProviderClass describes one secret object:
objectPathis the path to the secret defined in Vault. Prefaced with a forward-slash.objectNamea key name within that secretobjectVersion- the version of the secret. When none is specified the latest is retrieved.
Verify that the SecretProviderClass, named vault-database has been defined in
the default namespace.
$ kubectl describe SecretProviderClass vault-database
Name: vault-database
Namespace: default
## ...
»Create a pod with secret mounted
With the secret stored in Vault, the authentication configured and role created,
the provider-vault extension installed and the SecretProviderClass defined
it is finally time to create a pod that mounts the desired secret.
Apply the webapp pod that mounts the secrets volume.
$ cat <<EOF | kubectl apply -f -
kind: Pod
apiVersion: v1
metadata:
name: webapp
spec:
containers:
- image: jweissig/app:0.0.1
name: webapp
volumeMounts:
- name: secrets-store-inline
mountPath: "/mnt/secrets-store"
readOnly: true
volumes:
- name: secrets-store-inline
csi:
driver: secrets-store.csi.k8s.io
readOnly: true
volumeAttributes:
secretProviderClass: "vault-database"
EOF
pod/webapp created
The webapp pod defines and mounts a read-only volume to /mnt/secrets-store.
The objects defined in the vault-database SecretProviderClass are written as
files within that path.
Get all the pods within the default namespace.
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
csi-secrets-store-csi-driver-6rf2k 3/3 Running 0 13m
csi-secrets-store-provider-vault-qm44g 1/1 Running 0 8m
webapp 1/1 Running 0 5m
vault-0 1/1 Running 0 27m
Wait until the webapp pod is running and ready (1/1).
Display the password secret written to the file system at
/mnt/secrets-store/password on the webapp pod.
$ kubectl exec webapp -- cat /mnt/secrets-store/db-pass
db-secret-password
The value displayed matches the password value for the secret
secret/db-pass.
»Next steps
The Kubernetes Container Storage Interface (CSI) is an extensible approach to the management of storage alongside the lifecycle of containers. Learn more about the Secrets Store CSI driver and the Vault provider in this tutorial to accomplish the secrets management for the container.
Secrets mounted on ephemeral volumes is one approach to manage secrets for applications pods. Explore how pods can retrieve them directly via network requests and through the Vault Injector service via annotations.