Provisioning Identity through SDS

This task shows how to enable SDS (secret discovery service) for Istio identity provisioning.

Prior to Istio 1.1, the keys and certificates of Istio workloads were generated by Citadel and distributed to sidecars through secret-volume mounted files, this approach has the following minor drawbacks:

  • Performance regression during certificate rotation: When certificate rotation happens, Envoy is hot restarted to pick up the new key and certificate, causing performance regression.

  • Potential security vulnerability: The workload private keys are distributed through Kubernetes secrets, with known risks.

These issues are addressed in Istio 1.1 through the SDS identity provision flow. The workflow can be described as follows.

  1. The workload sidecar Envoy requests the key and certificates from the Citadel agent: The Citadel agent is a SDS server, which runs as per-node DaemonSet. In the request, Envoy passes a Kubernetes service account JWT to the agent.

  2. The Citadel agent generates a key pair and sends the CSR request to Citadel: Citadel verifies the JWT and issues the certificate to the Citadel agent.

  3. The Citadel agent sends the key and certificate back to the workload sidecar.

This approach has the following benefits:

  • The private key never leaves the node: It is only in the Citadel agent and Envoy sidecar’s memory.

  • The secret volume mount is no longer needed: The reliance on the Kubernetes secrets is eliminated.

  • The sidecar Envoy is able to dynamically renew the key and certificate through the SDS API: Certificate rotations no longer require Envoy to restart.

Before you begin

  • Set up Istio by following the instructions using Helm with SDS setup and global mutual TLS enabled:

    $ cat install/kubernetes/namespace.yaml > istio-auth-sds.yaml
    $ cat install/kubernetes/helm/istio-init/files/crd-* >> istio-auth-sds.yaml
    $ helm dep update --skip-refresh install/kubernetes/helm/istio
    $ helm template install/kubernetes/helm/istio --name istio --namespace istio-system --values @install/kubernetes/helm/istio/values-istio-sds-auth.yaml@ >> istio-auth-sds.yaml
    $ kubectl create -f istio-auth-sds.yaml

Service-to-service mutual TLS using key/certificate provisioned through SDS

Follow the authentication policy task to setup test services.

$ kubectl create ns foo
$ kubectl apply -f <(istioctl kube-inject -f @samples/httpbin/httpbin.yaml@) -n foo
$ kubectl apply -f <(istioctl kube-inject -f @samples/sleep/sleep.yaml@) -n foo
$ kubectl create ns bar
$ kubectl apply -f <(istioctl kube-inject -f @samples/httpbin/httpbin.yaml@) -n bar
$ kubectl apply -f <(istioctl kube-inject -f @samples/sleep/sleep.yaml@) -n bar

Verify all mutual TLS requests succeed:

$ for from in "foo" "bar"; do for to in "foo" "bar"; do kubectl exec $(kubectl get pod -l app=sleep -n ${from} -o jsonpath={}) -c sleep -n ${from} -- curl "http://httpbin.${to}:8000/ip" -s -o /dev/null -w "sleep.${from} to httpbin.${to}: %{http_code}\n"; done; done to 200 to 200 to 200 to 200

Verifying no secret-volume mounted file is generated

To verify that no secret-volume mounted file is generated, access the deployed workload sidecar container:

$ kubectl exec -it $(kubectl get pod -l app=sleep -n foo -o jsonpath={}) -c istio-proxy -n foo  -- /bin/bash

As you can see there is no secret file mounted at /etc/certs folder.


Clean up test services and Istio control plane:

$ kubectl delete ns foo
$ kubectl delete ns bar
$ kubectl delete -f istio-auth-sds.yaml


Currently, the SDS identity provision flow has the following caveats:

  • You still need secret volume mount for enabling the control plane security. Enabling SDS for the control plane security remains a work in progress.

  • Smoothly migrating a cluster from using secret volume mount to using SDS is a work in progress.