cert-manager

cert-manager is a tool that automates certificate management. This can be integrated with Istio gateways to manage TLS certificates.

Configuration

Consult the cert-manager installation documentation to get started. No special changes are needed to work with Istio.

Usage

Istio Gateway

cert-manager can be used to write a secret to Kubernetes, which can then be referenced by a Gateway.

  1. To get started, configure an Issuer resource, following the cert-manager issuer documentation. Issuers are Kubernetes resources that represent certificate authorities (CAs) that are able to generate signed certificates by honoring certificate signing requests. For example: an Issuer may look like:

    apiVersion: cert-manager.io/v1
    kind: Issuer
    metadata:
      name: ca-issuer
      namespace: istio-system
    spec:
      ca:
        secretName: ca-key-pair
    
  2. Next, configure a Certificate resource, following the cert-manager documentation. The Certificate should be created in the same namespace as the istio-ingressgateway deployment. For example, a Certificate may look like:

    apiVersion: cert-manager.io/v1
    kind: Certificate
    metadata:
      name: ingress-cert
      namespace: istio-system
    spec:
      secretName: ingress-cert
      commonName: my.example.com
      dnsNames:
      - my.example.com
      ...
    
  3. Once we have the certificate created, we should see the secret created in the istio-system namespace. This can then be referenced in the tls config for a Gateway under credentialName:

    apiVersion: networking.istio.io/v1
    kind: Gateway
    metadata:
      name: gateway
    spec:
      selector:
        istio: ingressgateway
      servers:
      - port:
          number: 443
          name: https
          protocol: HTTPS
        tls:
          mode: SIMPLE
          credentialName: ingress-cert # This should match the Certificate secretName
        hosts:
        - my.example.com # This should match a DNS name in the Certificate
    

Kubernetes Ingress

cert-manager provides direct integration with Kubernetes Ingress by configuring an annotation on the Ingress object. If this method is used, the Ingress must reside in the same namespace as the istio-ingressgateway deployment, as secrets will only be read within the same namespace.

Alternatively, a Certificate can be created as described in Istio Gateway, then referenced in the Ingress object:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: ingress
  annotations:
    kubernetes.io/ingress.class: istio
spec:
  rules:
  - host: my.example.com
    http: ...
  tls:
  - hosts:
    - my.example.com # This should match a DNS name in the Certificate
    secretName: ingress-cert # This should match the Certificate secretName
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