As Christopher mentions, you need to just add the annotation to the service, and it will automatically create an internal load balancer, instead an external one. The service will look like this:

apiVersion: v1
kind: Service
metadata:
  name: nginx-ingress
  namespace: nginx-ingress
  annotations:
    cloud.google.com/load-balancer-type: "Internal"
spec:
  externalTrafficPolicy: Local
  type: LoadBalancer
  ports:
  - port: 80
    targetPort: 80
    protocol: TCP
    name: http
  - port: 443
    targetPort: 443
    protocol: TCP
    name: https
  selector:
    app: nginx-ingress

Leave the rest of the objects as it is. If you want to have both; the external and the internal one, just create the internal one (below). They both can point to the same ingress controller.

Assuming you use ingress-nginx, then you can follow the steps on their Installation Guide page

You need to have your kubectl context pointed to your cluster (set it up by following this guide) before you can do these commands:

• Initialize your user as cluster-admin with the following command

  kubectl create clusterrolebinding cluster-admin-binding \
  --clusterrole cluster-admin \
  --user $(gcloud config get-value account)

• Deploy ingress-nginx using the following steps

  kubectl apply -f https://raw.githubusercontent.com/kubernetes/ingress-nginx/controller-0.32.0/deploy/static/provider/cloud/deploy.yaml

• Use a LoadBalancer service with annotation cloud.google.com/load-balancer-type: "Internal". This will spawn an internal ILB in your VPC

  apiVersion: v1
  kind: Service
  metadata:
    name: ingress-nginx-ilb-service
    namespace: ingress-nginx
    annotations:
      cloud.google.com/load-balancer-type: "Internal"
    labels:
      app.kubernetes.io/name: ingress-nginx
      app.kubernetes.io/instance: ingress-nginx
      app.kubernetes.io/component: controller
  spec:
    type: LoadBalancer
    selector:
      app.kubernetes.io/name: ingress-nginx
      app.kubernetes.io/instance: ingress-nginx
      app.kubernetes.io/component: controller
    ports:
      - name: http
        port: 80
        protocol: TCP
        targetPort: http
      - name: https
        port: 443
        protocol: TCP
        targetPort: https

Your ILB internal IP will be available in a few minutes after applying this service manifest