Custom CA Integration using Kubernetes CSR [Experimental]

This feature is actively in development and is considered experimental.

This feature requires Kubernetes version >= 1.18.

This task shows how to provision Workload Certificates using a custom certificate authority that integrates with the Kubernetes CSR API. This feature leverages Chiron, a lightweight component linked with Istiod that signs certificates using the Kubernetes CSR API.

This task is split into two parts. The first part demonstrates how to use the Kubernetes CA itself to sign workload certificates. The second part demonstrates how to use a custom CA that integrates with the Kubernetes CSR API to sign your certificates.

Part 1: Using Kubernetes CA

Note that this example should only be used for basic evaluation. The use of the kubernetes.io/legacy-unknown signer is NOT recommended in production environments.

Deploying Istio with Kubernetes CA

1. Deploy Istio on the cluster using istioctl with the following configuration.

   $ cat <<EOF > ./istio.yaml apiVersion: install.istio.io/v1alpha1 kind: IstioOperator spec: pilot: k8s: env: # Indicate to Istiod that we use an Custom Certificate Authority - name: EXTERNAL_CA value: ISTIOD_RA_KUBERNETES_API # Tells Istiod to use the Kubernetes legacy CA Signer - name: K8S_SIGNER value: kubernetes.io/legacy-unknown EOF $ istioctl install --set profile=demo -f ./istio.yaml

2. Deploy the bookinfo sample application in the bookinfo namespace. Ensure that the following commands are executed in the Istio root directory.

   $ kubectl create ns bookinfo $ kubectl apply -f <(istioctl kube-inject -f samples/bookinfo/platform/kube/bookinfo.yaml) -n bookinfo

Verify that the certificates installed are correct

When the workloads are deployed, above, they send CSR Requests to Istiod which forwards them to the Kubernetes CA for signing. If all goes well, the signed certificates are sent back to the workloads where they are then installed. To verify that they have been signed by the Kubernetes CA, you need to first extract the signed certificates.

1. Dump all pods running in the namespace.

   $ kubectl get pods -n bookinfo

   Pick any one of the running pods for the next step.

2. Get the certificate chain and CA root certificate used by the Istio proxies for mTLS.

   $ istioctl pc secret <pod-name> -o json > proxy_secret

   The proxy_secret json file contains the CA root certificate for mTLS in the trustedCA field. Note that this certificate is base64 encoded.

3. The certificate used by the Kubernetes CA (specifically the kubernetes.io/legacy-unknown signer) is loaded onto the secret associated with every service account in the bookinfo namespace.

   $ kubectl get secrets -n bookinfo

   Pick a secret-name that is associated with any of the service-accounts. These have a “token” in their name.

   $ kubectl get secrets -n bookinfo <secret-name> -o json

   The ca.crt field in the output contains the base64 encoded Kubernetes CA certificate.

4. Compare the ca.cert obtained in the previous step with the contents of the TrustedCA field in the step before. These two should be the same.

5. (Optional) Follow the rest of the steps in the bookinfo example to ensure that communication between services is working as expected.

Cleanup Part 1

• Remove the istio-system and bookinfo namespaces:

  $ kubectl delete ns istio-system $ kubectl delete ns bookinfo

Part 2: Using Custom CA

This assumes that the custom CA implements a controller that has the necessary permissions to read and sign Kubernetes CSR Requests. Refer to the Kubernetes CSR documentation for more details. Note that the steps below are dependent on an external-source and may change.

Deploy Custom CA controller in the Kubernetes cluster

1. For this example, we use an open-source Certificate Authority implementation. This code builds a controller that reads the CSR resources on the Kubernetes cluster and creates certificates using local keys. Follow the instructions on the page to:

   1. Build the Certificate-Controller docker image
   2. Upload the image to a Docker Registry
   3. Generate the Kubernetes manifest to deploy it

2. Deploy the Kubernetes manifest generated in the previous step on your local cluster in the signer-ca-system namespace.

   $ kubectl apply -f local-ca.yaml

Ensure that all the services are running.

$ kubectl get services -n signer-ca-system
  NAME                                           TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)    AGE
  signer-ca-controller-manager-metrics-service   ClusterIP   10.8.9.25    none        8443/TCP   72s

1. Get the public key of the CA. This is encoded in the secret “signer-ca-*” in the signer-ca-system namespace.

   $ kubectl get secrets signer-ca-5hff5h74hm -o json

The tls.crt field contains the base64 encoded public key file. Record this for future use.

Load the CA root certificate into a secret that istiod can access

1. Load the secret into the istiod namespace.

   $ cat <<EOF > ./external-ca-secret.yaml apiVersion: v1 kind: Secret metadata: name: external-ca-cert namespace: istio-system data: root-cert.pem: <tls.cert from the step above> EOF $ kubectl apply -f external-ca-secret.yaml

   This step is necessary for Istio to verify that the workload certificates have been signed by the correct certificate authority and to add the root-cert to the trust bundle for mTLS to work.

Deploying Istio

1. Deploy Istio on the cluster using istioctl with the following configuration.

   $ cat <<EOF > ./istio.yaml apiVersion: install.istio.io/v1alpha1 kind: IstioOperator spec: components: base: k8s: overlays: # Amend ClusterRole to add permission for istiod to approve certificate signing by custom signer - kind: ClusterRole name: istiod-istio-system patches: - path: rules[-1] value: | apiGroups: - certificates.k8s.io resourceNames: # Name of k8s external Signer in this example - example.com/foo resources: - signers verbs: - approve pilot: k8s: env: # Indicate to Istiod that we use an external signer - name: EXTERNAL_CA value: ISTIOD_RA_KUBERNETES_API # Indicate to Istiod the external k8s Signer Name - name: K8S_SIGNER value: example.com/foo overlays: - kind: Deployment name: istiod patches: - path: spec.template.spec.containers[0].volumeMounts[-1] value: | # Mount external CA certificate into Istiod name: external-ca-cert mountPath: /etc/external-ca-cert readOnly: true - path: spec.template.spec.volumes[-1] value: | name: external-ca-cert secret: secretName: external-ca-cert optional: true EOF $ istioctl install --set profile=demo -f ./istio.yaml

2. Deploy the bookinfo sample application in the bookinfo namespace.

   $ kubectl create ns bookinfo $ kubectl apply -f <(istioctl kube-inject -f samples/bookinfo/platform/kube/bookinfo.yaml) -n bookinfo

Verify that Custom CA certificates installed are correct

When the workloads are deployed, above, they send CSR Requests to Istiod which forwards them to the Kubernetes CA for signing. If all goes well, the signed certificates are sent back to the workloads where they are then installed. To verify that they have indeed been signed by the Kubernetes CA, you need to first extract the signed certificates.

1. Dump all pods running in the namespace.

   $ kubectl get pods -n bookinfo

Pick any of the running pods for the next step.

1. Get the certificate chain and CA root certificate used by the Istio proxies for mTLS.

   $ istioctl pc secret <pod-name> -o json > proxy_secret

The proxy_secret json file contains the CA root certificate for mTLS in the trustedCA field. Note that this certificate is base64 encoded.

1. Compare the CA root certificate obtained in the step above with “root-cert.pem” value in external-ca-cert. These two should be the same.

2. (Optional) Follow the rest of the steps in the bookinfo example to ensure that communication between services is working as expected.

Cleanup Part 2

• Remove the istio-system and bookinfo namespaces:

  $ kubectl delete ns istio-system $ kubectl delete ns bookinfo

Reasons to use this feature

• Added Security - Unlike plugin-ca-cert or the default self-signed option, enabling this feature means that the CA private keys need not be present in the Kubernetes cluster.

• Custom CA Integration - By specifying a Signer name in the Kubernetes CSR Request, this feature allows Istio to integrate with custom Certificate Authorities using the Kubernetes CSR API interface. This does require the custom CA to implement a Kubernetes controller to watch the CertificateSigningRequest and Certificate Resources and act on them.

See also

Change in Secret Discovery Service in Istio 1.3

Taking advantage of Kubernetes trustworthy JWTs to issue certificates for workload instances more securely.

Extending Istio Self-Signed Root Certificate Lifetime

Learn how to extend the lifetime of Istio self-signed root certificate.

Istio DNS Certificate Management

Shows how to provision and manage DNS certificates in Istio.

Migrate pre-Istio 1.4 Alpha security policy to the current APIs

A tutorial to help customers migrate from the deprecated v1alpha1 security policy to the supported v1beta1 version.

Provision a certificate and key for an application without sidecars

A mechanism to acquire and share an application certificate and key through mounted files.

Istio in 2020 - Following the Trade Winds

A vision statement and roadmap for Istio in 2020.