Custom CA Integration using Kubernetes CSR (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 . 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.

Note that this example should only be used for basic evaluation. The use of the signer is NOT recommended in production environments.

1. 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

   $ 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 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 to ensure that communication between services is working as expected.

• Remove the istio-system and bookinfo namespaces:

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

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 . 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

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.

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

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 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

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

• 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 Resources and act on them.