I want to add a wild card based domain name (e.g *.somedomain.com) to istio-ingressgateway and set self-signed TLS certificate. Istio on GKE is installed via enabling Istio from the cluster's addon list.

First question is whether it is recommended to configure and use the auto-generated istio-ingressgateway instead of creating one.

If so, then the second question is how to update the settings for that gateway.

I had to include labels, resourceVersion and selfLink fields from the auto-created ingressgateway and set resourceVersion as the current version, otherwise, Kubernetes does not accept the new YAML file.

apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  # QUESTION: Copid fields from the current ingressgateway to be specified.
  # Otherwise, kubectl does not accept the settings.
  # $ kubectl apply -f ./helm-charts/istio/gateway.yaml
  # The gateways "istio-autogenerated-k8s-ingress" is invalid: metadata.resourceVersion: Invalid value: 0x0: must be specified for an update

  # labels:
  #   addonmanager.kubernetes.io/mode: EnsureExists
  #   k8s-app: istio
  # resourceVersion: "9331065"
  # selfLink: /apis/networking.istio.io/v1alpha3/namespaces/istio-system/gateways/istio-autogenerated-k8s-ingressa
  name: istio-autogenerated-k8s-ingress
  namespace: istio-system
spec:
  selector:
    istio: ingressgateway
  servers:
  - port:
      number: 443
      name: https
      protocol: HTTPS
    tls:
      mode: PASSTHROUGH
      serverCertificate: /etc/istio/ingressgateway-certs/tls.crt
      privateKey: /etc/istio/ingressgateway-certs/tls.key
    hosts:
    - "*.heportal.squiz.cloud"

If I apply the above sample gateway.yaml file:

$ kubectl apply -f ./helm-charts/istio/gateway.yaml
The gateways "istio-autogenerated-k8s-ingress" is invalid: metadata.resourceVersion: Invalid value: 0x0: must be specified for an update