Configure Vault as a Certificate Manager in Kubernetes with Helm

15min
|
Vault

Kubernetes configured to use Vault as a certificate manager enables your services to establish their identity and communicate securely over the network with other services or clients internal or external to the cluster.

Jetstack's cert-manager enables Vault's PKI secrets engine to dynamically generate X.509 certificates within Kubernetes through an Issuer interface.

In this tutorial, you set up Vault with the Vault Helm chart, configure the PKI secrets engine and Kubernetes authentication. Then install Jetstack's cert-manager, configure it to use Vault, and request a certificate.

Prerequisites

This tutorial requires the Kubernetes command-line interface (CLI) and the Helm CLI installed, Minikube, the Vault Helm charts, the sample web application, and additional configuration to bring it all together.

This tutorial was last tested 29 Apr 2020 on a macOS 10.15.4 using this configuration.

Docker version.

$ docker version
Client: Docker Engine - Community
  Version:          19.03.8
  ## ...

Minikube version.

$ minikube version
minikube version: v1.8.2
commit: eb13446e786c9ef70cb0a9f85a633194e62396a1

Helm version.

$ helm version
version.BuildInfo{Version:"v3.1.2", GitCommit:"d878d4d45863e42fd5cff6743294a11d28a9abce", GitTreeState:"clean", GoVersion:"go1.14"}

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 for installing 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

Next, retrieve the web application and additional configuration by cloning the hashicorp/vault-guides repository from GitHub.

$ git clone https://github.com/hashicorp/vault-guides.git

This repository contains supporting content for all of the Vault learn guides. The content specific to this tutorial can be found within a sub-directory.

Go into the vault-guides/operations/provision-vault/kubernetes/minikube/external-vault directory.

$ cd vault-guides/operations/provision-vault/kubernetes/minikube/external-vault

Working directory

This tutorial assumes that the remainder of commands are executed within this directory.

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 v1.8.2 on Darwin 10.15.4
✨  Automatically selected the hyperkit driver
🔥  Creating hyperkit VM (CPUs=2, Memory=4000MB, Disk=20000MB) ...
🐳  Preparing Kubernetes v1.17.3 on Docker 19.03.6 ...
🚀  Launching Kubernetes ...
🌟  Enabling addons: default-storageclass, storage-provisioner
⌛  Waiting for cluster to come online ...
🏄  Done! kubectl is now configured to use "minikube"

Verify the status of the Minikube cluster.

$ minikube status
host: Running
kubelet: Running
apiserver: Running
kubeconfig: Configured

Additional waiting

Even if the previous step completed successfully, you may have to wait for Minikube to be available. If you see an error, try again after a few minutes.

The host, kubelet, and 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

Add the HashiCorp Helm repository.

$ helm repo add hashicorp https://helm.releases.hashicorp.com
"hashicorp" has been added to your repositories

Update all the repositories to ensure helm is aware of the latest versions.

$ helm repo update
Hang tight while we grab the latest from your chart repositories...
...Successfully got an update from the "hashicorp" chart repository
Update Complete. ⎈Happy Helming!⎈

Install the latest version of the Vault server running in standalone mode with the Vault Agent Injector service disabled.

$ helm install vault hashicorp/vault --set "injector.enabled=false"
NAME: vault
## ...

The Vault server runs in standalone mode on a single pod. By default the Helm chart starts a Vault Agent Injector pod but that is disabled injector.enabled=false.

Get all the pods within the default namespace.

$ kubectl get pods
NAME      READY   STATUS    RESTARTS   AGE
vault-0   0/1     Running   0          87s

The vault-0 pod is deployed. The Vault server running in the pod's container reports that it is running but it is not ready (0/1). To ready the pod requires that the Vault server is initialized and unsealed.

Get all the services within the default namespace.

$ kubectl get service
NAME         TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)             AGE
kubernetes   ClusterIP   10.96.0.1       <none>        443/TCP             9m5s
vault        ClusterIP   10.105.21.154   <none>        8200/TCP,8201/TCP   2m34s

The Vault Helm chart creates a Service that directs requests to the Vault pod. This enables us to address the Vault server within the cluster with the address http://vault.default:8200.

Initialize and unseal Vault

Vault run in standalone mode starts uninitialized and in the sealed state. Prior to initialization the storage backend is not prepared to receive data.

Initialize Vault with one key share and one key threshold.

$ kubectl exec vault-0 -- vault operator init -key-shares=1 -key-threshold=1 \
      -format=json > init-keys.json

The operator init command generates a root key that it disassembles into key shares -key-shares=1 and then sets the number of key shares required to unseal Vault -key-threshold=1. These key shares are written to the output as unseal keys in JSON format -format=json. Here the output is redirected to a local file named init-keys.json

View the unseal key found in init-keys.json.

$ cat init-keys.json | jq -r ".unseal_keys_b64[]"
hmeMLoRiX/trBTx/xPZHjCcZ7c4H8OCt2Njkrv2yXZY=

Insecure operation

Do not run an unsealed Vault in production with a single key share and a single key threshold. This approach is only used here to simplify the unsealing process for this demonstration.

Create a variable named VAULT_UNSEAL_KEY to capture the Vault unseal key.

$ VAULT_UNSEAL_KEY=$(cat init-keys.json | jq -r ".unseal_keys_b64[]")

After initialization, Vault is configured to know where and how to access the storage, but does not know how to decrypt any of it. Unsealing is the process of constructing the root key necessary to read the decryption key to decrypt the data, allowing access to the Vault.

Unseal Vault running on the vault-0 pod with the $VAULT_UNSEAL_KEY.

$ kubectl exec vault-0 -- vault operator unseal $VAULT_UNSEAL_KEY
Key             Value
---             -----
Seal Type       shamir
Initialized     true
Sealed          false
Total Shares    1
Threshold       1
Version         1.4.0
Cluster Name    vault-cluster-3ecefcf2
Cluster ID      0998f747-af15-f994-cded-295836b718d6
HA Enabled      false

The operator unseal command reports that Vault is initialized and unsealed.

Insecure operation

Providing the unseal key with the command writes the key to your shell's history. This approach is only used here to simplify the unsealing process for this demonstration.

Get all the pods within the default namespace.

$ kubectl get pods
NAME                                    READY   STATUS    RESTARTS   AGE
vault-0                                 1/1     Running   0          5m49s

The vault-0 pod reports that it is ready 1/1. Vault is ready for you to login with the root token generated during the initialization.

View the root token found in init-keys.json.

$ cat init-keys.json | jq -r ".root_token"
s.XzExf8TjRVYKm85xMATa6Q7U

Create a variable named VAULT_ROOT_TOKEN to capture the root token.

$ VAULT_ROOT_TOKEN=$(cat init-keys.json | jq -r ".root_token")

$ kubectl exec vault-0 -- vault login $VAULT_ROOT_TOKEN

Success! You are now authenticated. The token information displayed below
is already stored in the token helper. You do NOT need to run "vault login"
again. Future Vault requests will automatically use this token.

Key                  Value
---                  -----
token                s.P3Koh6BZikQPDxPSNwDzmKJ5
token_accessor       kHFYypyS2EcYpMyrsyXUQmNa
token_duration       ∞
token_renewable      false
token_policies       ["root"]
identity_policies    []
policies             ["root"]

The Vault server is ready to be configured as a certificate store.

Configure PKI secrets engine

First, start an interactive shell session on the vault-0 pod.

$ kubectl exec --stdin=true --tty=true 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 PKI secrets engine at its default path.

$ vault secrets enable pki
Success! Enabled the pki secrets engine at: pki/

By default the KPI secrets engine sets the time-to-live (TTL) to 30 days. A certificate can have its lease extended to ensure certificate rotation on a yearly basis (8760h).

Configure the max lease time-to-live (TTL) to 8760h.

$ vault secrets tune -max-lease-ttl=8760h pki
Success! Tuned the secrets engine at: pki/

Vault can accept an existing key pair, or it can generate its own self-signed root. In general, we recommend maintaining your root CA outside of Vault and providing Vault a signed intermediate CA.

Generate a self-signed certificate valid for 8760h.

$ vault write pki/root/generate/internal \
    common_name=example.com \
    ttl=8760h

Example output:

Key              Value
---              -----
certificate      -----BEGIN CERTIFICATE-----
## ...
-----END CERTIFICATE-----
expiration       1619120269
issuing_ca       -----BEGIN CERTIFICATE-----
## ...
-----END CERTIFICATE-----
serial_number    65:37:b5:b3:91:6c:7b:d8:33:22:03:28:b1:58:ff:be:8a:72:a4:c0

Configure the PKI secrets engine certificate issuing and certificate revocation list (CRL) endpoints to use the Vault service in the default namespace.

$ vault write pki/config/urls \
    issuing_certificates="http://vault.default:8200/v1/pki/ca" \
    crl_distribution_points="http://vault.default:8200/v1/pki/crl"

Output:

Success! Data written to: pki/config/urls

Configure a role named example-dot-com that enables the creation of certificates example.com domain with any subdomains.

$ vault write pki/roles/example-dot-com \
    allowed_domains=example.com \
    allow_subdomains=true \
    max_ttl=72h

Output:

Success! Data written to: pki/roles/example-dot-com

The role, example-dot-com, is a logical name that maps to a policy used to generate credentials. This generates a number of endpoints that are used by the Kubernetes service account to issue and sign these certificates. A policy must be created that enables these paths.

Create a policy named pki that enables read access to the PKI secrets engine paths.

$ vault policy write pki - <<EOF
path "pki*"                        { capabilities = ["read", "list"] }
path "pki/sign/example-dot-com"    { capabilities = ["create", "update"] }
path "pki/issue/example-dot-com"   { capabilities = ["create"] }
EOF

Output:

Success! Uploaded policy: pki

These paths enable the token to view all the roles created for this PKI secrets engine and access the sign and issues operations for the example-dot-com role.

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.

First, start an interactive shell session on the vault-0 pod.

$ kubectl exec --stdin=true --tty=true 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 location of the Kubernetes API.

For the best compatibility with recent Kubernetes versions, ensure you are using Vault v1.9.3 or greater.

$ vault write auth/kubernetes/config \
    kubernetes_host="https://$KUBERNETES_PORT_443_TCP_ADDR:443"

Output:

Success! Data written to: auth/kubernetes/config

The environment variable KUBERNETES_PORT_443_TCP_ADDR references the internal network address of the Kubernetes host.

You can validate the issuer name of your Kubernetes cluster using this method.

Finally, create a Kubernetes authentication role named issuer that binds the pki policy with a Kubernetes service account named issuer.

$ vault write auth/kubernetes/role/issuer \
    bound_service_account_names=issuer \
    bound_service_account_namespaces=default \
    policies=pki \
    ttl=20m

Output:

Success! Data written to: auth/kubernetes/role/issuer

The role connects the Kubernetes service account, issuer, in the default namespace with the pki Vault policy. The tokens returned after authentication are valid for 20 minutes. This Kubernetes service account name, issuer, is created in the Deploy Issuer and Certificate section.

Lastly, exit the vault-0 pod.

$ exit

Deploy Cert Manager

Jetstack's cert-manager is a Kubernetes add-on that automates the management and issuance of TLS certificates from various issuing sources. Vault can be configured as one of those sources. The cert-manager requires the creation of a set of Kubernetes resources that provide the interface to the certificate creation.

Install Jetstack's cert-manager's version 0.14.3 resources.

$ kubectl apply --validate=false -f https://github.com/jetstack/cert-manager/releases/download/v0.14.3/cert-manager.crds.yaml
customresourcedefinition.apiextensions.k8s.io/challenges.acme.cert-manager.io created
customresourcedefinition.apiextensions.k8s.io/orders.acme.cert-manager.io created
customresourcedefinition.apiextensions.k8s.io/certificaterequests.cert-manager.io created
customresourcedefinition.apiextensions.k8s.io/certificates.cert-manager.io created
customresourcedefinition.apiextensions.k8s.io/clusterissuers.cert-manager.io created
customresourcedefinition.apiextensions.k8s.io/issuers.cert-manager.io created

Create a namespace named cert-manager to host the cert-manager.

$ kubectl create namespace cert-manager
namespace/cert-manager created

Jetstack's cert-manager Helm chart is available in a repository that they maintain. Helm can request and install Helm charts from these custom repositories.

Add the jetstack chart repository.

$ helm repo add jetstack https://charts.jetstack.io
"jetstack" has been added to your repositories

Helm maintains a cached list of charts for every repository that it maintains. This list needs to be updated periodically so that Helm knows about all available charts and their releases. A repository recently added needs to be updated before any chart is requested.

Update the local list of Helm charts.

$ helm repo update
Hang tight while we grab the latest from your chart repositories...
...Successfully got an update from the "jetstack" chart repository
Update Complete. ⎈ Happy Helming!⎈

The results show that the jetstack chart repository has retrieved an update.

Install the cert-manager chart version 0.11 in the cert-manager namespace.

$ helm install cert-manager \
    --namespace cert-manager \
    --version v0.14.3 \
   jetstack/cert-manager

Output:

NAME: cert-manager
## ...

The cert-manager chart deploys a number of pods within the cert-manager namespace.

Get all the pods within the cert-manager namespace.

$ kubectl get pods --namespace cert-manager
NAME                                       READY   STATUS    RESTARTS   AGE
cert-manager-66958f45fc-pdf64              1/1     Running   0          27s
cert-manager-cainjector-755bbf9c6b-gpgtg   1/1     Running   0          27s
cert-manager-webhook-76954fcbcd-w4lll      1/1     Running   0          27s

Wait until the pods prefixed with cert-manager are running and ready (1/1).

Thes pods now require configuration to interface with Vault.

Configure an issuer and generate a certificate

The cert-manager enables you to define Issuers that interface with the Vault certificate generating endpoints. These Issuers are invoked when a Certificate is created.

When you configured Vault's Kubernetes authentication a Kubernetes service account, named issuer, was granted the policy, named pki, to the certificate generation endpoints.

Create a service account named issuer within the default namespace.

$ kubectl create serviceaccount issuer
serviceaccount/issuer created

The service account generated a secret that is required by the Issuer automatically in Kubernetes 1.23. In Kubernetes 1.24+, you need to create the secret explicitly.

issuer-secret.yaml

apiVersion: v1
kind: Secret
metadata:
  name: issuer-token-lmzpj
  annotations:
    kubernetes.io/service-account.name: issuer
type: kubernetes.io/service-account-token

Kubernetes 1.24+ only

$ kubectl apply -f issuer-secret.yaml
secret/issuer-token-lmzpj created

Get all the secrets in the default namespace.

$ kubectl get secrets
default-token-mlm2n           kubernetes.io/service-account-token   3      13d
issuer-token-lmzpj            kubernetes.io/service-account-token   3      47s
sh.helm.release.v1.vault.v1   helm.sh/release.v1                    1      28m
vault-token-749nd             kubernetes.io/service-account-token   3      28m

The issuer secret is displayed here as the secret prefixed with issuer-token.

Create a variable named ISSUER_SECRET_REF to capture the secret name.

$ ISSUER_SECRET_REF=$(kubectl get secrets --output=json | jq -r '.items[].metadata | select(.name|startswith("issuer-token-")).name')

Define an Issuer, named vault-issuer, that sets Vault as a certificate issuer.

$ cat > vault-issuer.yaml <<EOF
apiVersion: cert-manager.io/v1alpha2
kind: Issuer
metadata:
  name: vault-issuer
  namespace: default
spec:
  vault:
    server: http://vault.default
    path: pki/sign/example-dot-com
    auth:
      kubernetes:
        mountPath: /v1/auth/kubernetes
        role: issuer
        secretRef:
          name: $ISSUER_SECRET_REF
          key: token
EOF

Create the vault-issuer Issuer.

$ kubectl apply --filename vault-issuer.yaml
issuer.cert-manager.io/vault-issuer created

The specification defines the signing endpoint and the authentication endpoint and credentials.

metadata.name sets the name of the Issuer to vault-issuer
spec.vault.server sets the server address to the Kubernetes service created in the default namespace
spec.vault.path is the signing endpoint created by Vault's PKI example-dot-com role
spec.vault.auth.kubernetes.mountPath sets the Vault authentication endpoint
spec.vault.auth.kubernetes.role sets the Vault Kubernetes role to issuer
spec.vault.auth.kubernetes/secretRef.name sets the secret for the Kubernetes service account
spec.vault.auth.kubernetes/secretRef.key sets the type to token.

Define a certificate named example-com.

$ cat > example-com-cert.yaml <<EOF
apiVersion: cert-manager.io/v1alpha2
kind: Certificate
metadata:
  name: example-com
  namespace: default
spec:
  secretName: example-com-tls
  issuerRef:
    name: vault-issuer
  commonName: www.example.com
  dnsNames:
  - www.example.com
EOF

The Certificate, named example-com, requests from Vault the certificate through the Issuer, named vault-issuer. The common name and DNS names are names within the allowed domains for the configured Vault endpoint.

Create the example-com certificate.

$ kubectl apply --filename example-com-cert.yaml
certificate.cert-manager.io/example-com created

View the details of the example-com certificate.

$ kubectl describe certificate.cert-manager example-com
Name:         example-com
Namespace:    default
## ...
Events:
  Type    Reason        Age   From          Message
  ----    ------        ----  ----          -------
  Normal  GeneratedKey  10m   cert-manager  Generated a new private key
  Normal  Requested     10m   cert-manager  Created new CertificateRequest resource "example-com-1072521490"
  Normal  Issued        70s   cert-manager  Certificate issued successfully

The certificate reports that it has been issued successfully.

Next steps

In this tutorial, you installed Vault configured the PKI secrets engine and Kubernetes authentication. Then installed Jetstack's cert-manager, configured it to use Vault, and requested a certificate.

Besides creation, these certificates can be revoked and removed. Learn more about Jetstack's cert-manager used in this tutorial and explore Vault's PKI secrets engine as a certificate authority in the Build Your Own Certificate Authority.