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Istio and cert-manager integration

Istio provides different mechanisms to sign workload certificates for the purpose of mutual TLS (mTLS). The options include:

  1. Istio Certificate Authority (CA) uses a self-signed root certificate
  2. Istio CA uses an administrator-specified certificate and key with an administrator-specified root certificate
  3. Custom CA issues keys and certificate files mounted into the sidecars
  4. Custom CA integration uses Kubernetes CSR API
  5. External CA uses Istio CA gRPC API (either through the Istiod Registration Authority (RA) model or directly authenticating workloads and validating Subject Alternative Name (SAN))

This guide explains how to integrate with cert-manager.

cert-manager CA Integration

This task shows how to provision Control Plane and Workload Certificates with an external Certificate Authority using cert-manager. cert-manager is a x509 certificate operator for Kubernetes that supports a number of Issuers, representing Certificate Authorities that can sign certificates. The istio-csr project installs an agent that is responsible for verifying incoming certificate signing requests from Istio mesh workloads, and signs them through cert-manager via a configured Issuer.

  1. Install cert-manager

    First, cert-manager must be installed on the cluster using your preferred method.

    helm repo add jetstack
    helm repo update
    kubectl create namespace cert-manager
    helm install -n cert-manager cert-manager jetstack/cert-manager --set installCRDs=true

    Verify the cert-manager deployments have successfully rolled-out.

    for i in cert-manager cert-manager-cainjector cert-manager-webhook; \
    do kubectl rollout status deploy/$i -n cert-manager; done
  2. Configure cert-manager

    An Issuer must be created in the istio-system namespace to sign Istiod and mesh workload certificates. We will use a SelfSigned Issuer, though any supported Issuer can be used.

    Use a Private CA

    Publicly trusted certificates are strongly discouraged from being used, including ACME certificates.

    kubectl create namespace istio-system

    kubectl apply -n istio-system -f - <<EOF
    kind: Issuer
    name: selfsigned
    selfSigned: {}
    kind: Certificate
    name: istio-ca
    isCA: true
    duration: 2160h # 90d
    secretName: istio-ca
    commonName: istio-ca
    - cert-manager
    name: selfsigned
    kind: Issuer
    kind: Issuer
    name: istio-ca
    secretName: istio-ca

    Verify the "istio-ca" and "self-signed" issuers are present and report READY=True:

    kubectl get issuers -n istio-system

    Once the issuers have become ready, istio-csr can be installed into the cluster.

  3. Install istio-csr

    helm install -n cert-manager cert-manager-istio-csr jetstack/cert-manager-istio-csr

    Verify the istio-csr deployment has successfully rolled-out.

    kubectl rollout status deploy/cert-manager-istio-csr -n cert-manager

    Certificates istio-ca and istiod should be present and report READY=True.

    kubectl get certificates -n istio-system
  4. Install Istio

    Istio must be configured to use cert-manager as the CA server for both workload and Istio control plane components. The following configuration uses the IstioOperator resource to install Istio with cert-manager integration:

    istioctl install -y -f - <<EOF
    kind: IstioOperator
    namespace: istio-system
    # Changes the certificate provider to Cert Manager istio-csr
    caAddress: cert-manager-istio-csr.cert-manager.svc:443
    # Disables istiod CA Server functionality
    - name: ENABLE_CA_SERVER
    value: "false"
    - apiVersion: apps/v1
    kind: Deployment
    name: istiod
    # Mounts istiod serving and webhook certificates from Secret
    - path: spec.template.spec.containers.[name:discovery].args[-1]
    value: "--tlsCertFile=/etc/cert-manager/tls/tls.crt"
    - path: spec.template.spec.containers.[name:discovery].args[-1]
    value: "--tlsKeyFile=/etc/cert-manager/tls/tls.key"
    - path: spec.template.spec.containers.[name:discovery].args[-1]
    value: "--caCertFile=/etc/cert-manager/ca/root-cert.pem"
    - path: spec.template.spec.containers.[name:discovery].volumeMounts[-1]
    name: cert-manager
    mountPath: "/etc/cert-manager/tls"
    readOnly: true
    - path: spec.template.spec.containers.[name:discovery].volumeMounts[-1]
    name: ca-root-cert
    mountPath: "/etc/cert-manager/ca"
    readOnly: true
    - path: spec.template.spec.volumes[-1]
    name: cert-manager
    secretName: istiod-tls
    - path: spec.template.spec.volumes[-1]
    name: ca-root-cert
    defaultMode: 420
    name: istio-ca-root-cert

    The installation should complete, and the Istio control plane should become in a ready state.

    kubectl get pods -n istio-system
  5. Test mTLS

    All workload certificates will now be requested through cert-manager using the configured Issuer. Let's run an example workload to test mTLS. First, create a namespace and configure it for automatic sidecar injection:

    kubectl create ns foo
    kubectl label ns/foo istio-injection=enabled

    Run the sample sleep and httpbin workloads.

    kubectl apply -n foo -f$ISTIO_VERSION/samples/sleep/sleep.yaml
    kubectl apply -n foo -f$ISTIO_VERSION/samples/httpbin/httpbin.yaml

    Verify the sleep and httpbin deployments have successfully rolled-out.

    for i in sleep httpbin; do kubectl rollout status -n foo deploy/$i; done

    Verify the sidecar proxy was injected for each workload. Each workload pod should show 2/2 containers are READY.

    for i in sleep httpbin; do kubectl get po -n foo -l app=$i; done

    By default, Istio configures destination workloads using PERMISSIVE mode. This mode means a service can accept both plain text and mTLS connections. To ensure mTLS is being used between sleep and httpbin workloads, set the mode to STRICT for namespace "foo".

    kubectl apply -n foo -f - <<EOF
    kind: PeerAuthentication
    name: "default"
    mode: STRICT

    Test mTLS from the sleep pod to the httpbin pod.

    kubectl -n foo exec -it deploy/sleep -c sleep -- curl -o /dev/null -s -w '%{http_code}\n'

    You should receive an 200 response code.

  6. Visualize mTLS

    Optionally, you can run Kiali to visualize the mTLS connections.

    kubectl apply -f$ISTIO_VERSION/samples/addons/prometheus.yaml
    kubectl apply -f$ISTIO_VERSION/samples/addons/kiali.yaml

    Verify the Kiali and Prometheus deployments successfully rolled-out.

    for i in prometheus kiali; do kubectl rollout status -n istio-system deploy/$i; done

    Open the Kiali dashboard.

    istioctl dashboard kiali

    Navigate to Workloads > Namespace:foo > httpbin. You should see the connection graph with padlocks to indicate mTLS is being used. If the graph is empty, adjust the "traffic metrics per refresh" dropdown list in the upper right-hand corner or regenerate connections.

Congratulations! You have successfully configured Istio to use cert-manager as a CA for mesh mTLS authentication.