gcloud compute networks create ${vpc_name}
--project=${project_id}
--bgp-routing-mode=regional
--subnet-mode=custom

gcloud compute networks subnets create ${subnet_name}
--project=${project_id}
--region=${region}
--network=${vpc_name}
--range=192.168.0.0/16

gcloud compute addresses create ${external_ip_name}
--region=${region}

gcloud compute routers create ${router_name}
--region=${region}
--network=${vpc_name}
--asn=65001

gcloud compute routers nats create ${nat_name}
--region=${region}
--router=${router_name}
--nat-external-ip-pool="${external_ip}"
--nat-all-subnet-ip-ranges

gcloud container clusters create ${gke_cluster_name}
--project=${project_id}
--zone=${zone}
--network=${vpc_name}
--subnetwork=${subnet_name}
--enable-ip-alias
--enable-private-nodes
--master-ipv4-cidr=172.16.0.0/28
--enable-master-authorized-networks
--master-authorized-networks=0.0.0.0/0
--no-enable-legacy-authorization
--no-enable-basic-auth
--no-issue-client-certificate
--num-nodes=${NUM_NODE}
--enable-autoscaling --max-nodes=${MAX_NUM} --min-nodes=${MIN_NUM}
--scopes="cloud-platform"

Make a https-connection from the application to an other gcp-project's application.
And catch the IP address of origin-request as 'REMOTE_ADDR'.