cert-manager

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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.

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
```
For a common Issuer type, ACME, a pod and service are created to respond to challenge requests in order to verify the client owns the domain. To respond to those challenges, an endpoint at http://<YOUR_DOMAIN>/.well-known/acme-challenge/<TOKEN> will need to be reachable. That configuration may be implementation specific.
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
  ...
```

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/v1alpha3
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/v1beta1
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