Configure private IP connectivity for Cloud SQL for PostgreSQL destinations

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#!/bin/bash

# Create the VPC network for the Database Migration Service Private Service Connect.
gcloud compute networks create dms-psc-vpc \
--project=PROJECT_ID \
--subnet-mode=custom

# Create a subnet for the Database Migration Service Private Service Connect.
gcloud compute networks subnets create dms-psc-REGION \
--project=PROJECT_ID \
--range=10.0.0.0/16 --network=dms-psc-vpc \
--region=REGION

# Create a router required for the bastion to be able to install external
# packages (for example, Dante SOCKS server):
gcloud compute routers create ex-router-REGION \
--network dms-psc-vpc \
--project=PROJECT_ID \
--region=REGION

gcloud compute routers nats create ex-nat-REGION \
--router=ex-router-REGION \
--auto-allocate-nat-external-ips \
--nat-all-subnet-ip-ranges \
--enable-logging \
--project=PROJECT_ID \
--region=REGION

# Create the bastion VM.
gcloud compute instances create BASTION \
    --project=PROJECT_ID \
    --zone=ZONE \
    --image-family=debian-11 \
    --image-project=debian-cloud \
    --network-interface subnet=dms-psc-REGION,no-address \
    --network-interface subnet=DB_SUBNETWORK,no-address \
    --metadata=startup-script='#!/bin/bash

# Route the private IP address using the gateway of the database subnetwork.
# Find the gateway for the relevant subnetwork on the VPC network page
# in the Google Cloud console. Click VPC networks and select the database VPC
# to see the details.
ip route add CLOUD_SQL_INSTANCE_PRIVATE_IP via DB_SUBNETWORK_GATEWAY

# Install Dante SOCKS server.
apt-get install -y dante-server

# Create the Dante configuration file.
touch /etc/danted.conf

# Create a proxy.log file.
touch proxy.log

# Add the following configuration for Dante:
cat > /etc/danted.conf << EOF
logoutput: /proxy.log
user.privileged: proxy
user.unprivileged: nobody

internal: 0.0.0.0 port = PORT
external: ens5

clientmethod: none
socksmethod: none

client pass {
        from: 0.0.0.0/0
        to: 0.0.0.0/0
        log: connect error disconnect
}
client block {
        from: 0.0.0.0/0
        to: 0.0.0.0/0
        log: connect error
}
socks pass {
        from: 0.0.0.0/0
        to: CLOUD_SQL_INSTANCE_PRIVATE_IP/32
        protocol: tcp
        log: connect error disconnect
}
socks block {
        from: 0.0.0.0/0
        to: 0.0.0.0/0
        log: connect error
}
EOF

# Start the Dante server.
systemctl restart danted

tail -f proxy.log'

# Create the target instance from the created bastion VM.
gcloud compute target-instances create bastion-ti-REGION \
--instance=BASTION \
--project=PROJECT_ID \
--instance-zone=ZONE \
--network=dms-psc-vpc

# Create a forwarding rule for the backend service.
gcloud compute forwarding-rules create dms-psc-forwarder-REGION \
--project=PROJECT_ID \
--region=REGION \
--load-balancing-scheme=internal \
--network=dms-psc-vpc \
--subnet=dms-psc-REGION \
--ip-protocol=TCP \
--ports=all \
--target-instance=bastion-ti-REGION \
--target-instance-zone=ZONE

# Create a TCP NAT subnet.
gcloud compute networks subnets create dms-psc-nat-REGION-tcp \
--network=dms-psc-vpc \
--project=PROJECT_ID \
--region=REGION \
--range=10.1.0.0/16 \
--purpose=private-service-connect

# Create a service attachment.
gcloud compute service-attachments create dms-psc-svc-att-REGION \
--project=PROJECT_ID \
--region=REGION \
--producer-forwarding-rule=dms-psc-forwarder-REGION \
--connection-preference=ACCEPT_MANUAL \
--nat-subnets=dms-psc-nat-REGION-tcp

# Create a firewall rule allowing the Private Service Connect NAT subnet.
# access the Private Service Connect subnet
gcloud compute \
--project=PROJECT_ID firewall-rules create dms-allow-psc-tcp \
--direction=INGRESS \
--priority=1000 \
--network=dms-psc-vpc \
--action=ALLOW \
--rules=all \
--source-ranges=10.1.0.0/16 \
--enable-logging

# Print out the created service attachment.
gcloud compute service-attachments describe dms-psc-svc-att-REGION \
--project=PROJECT_ID \
--region=REGION

variable "project_id" {
  type        = string
  description = <<DESC
The Google Cloud project in which the setup is created. This should be the same project as
the one that the Cloud SQL instance belongs to.
DESC
}

variable "region" {
  type        = string
  description = "The Google Cloud region in which you create the Private Service Connect
regional resources."
}

variable "zone" {
  type        = string
  description = <<DESC
The Google Cloud zone in which you create the Private Service Connect zonal resources
(should be in the same region as the one specified in the "region" variable).
DESC
}

variable "cloud_sql_instance_name" {
  type        = string
  description = "The Cloud SQL instance name."
}

variable "port" {
  type        = string
  description = "The port that the bastion will use to expose the underlying database."
  default     = "5432"
}

variable "cloud_sql_instance_network" {
  type        = string
  description = <<DESC
The VPC to which the Cloud SQL instance is peered. This is where the bastion will
forward connections to (the destination database needs to be accessible in this VPC).
DESC
}

/* To execute the call:
terraform apply
-var="project_id=PROJECT_ID"
-var="region=REGION"
-var="zone=ZONE"
-var="cloud_sql_instance_name=CLOUD_SQL_INSTANCE_NAME"
-var="port=PORT"
-var="cloud_sql_instance_network=CLOUD_SQL_INSTANCE_NETWORK" */

locals {
  cloud_sql_instance_connection_name = "${var.project_id}:${var.region}:${var.cloud_sql_instance_name}"
}

# Needed for getting the private IP address of the Cloud SQL instance.
data "google_sql_database_instance" "csql_instance" {
  name    = var.cloud_sql_instance_name
  project = var.project_id
}

# Needed for getting the IPv4 gateway of the subnetwork for the database.
data "google_compute_subnetwork" "db_network_subnet" {
  name    = var.cloud_sql_instance_network
  project = var.project_id
  region  = var.region
}

resource "google_compute_network" "psc_sp_network" {
  name                    = "dms-psc-network"
  project                 = var.project_id
  auto_create_subnetworks = false
}

resource "google_compute_subnetwork" "psc_sp_subnetwork" {
  name    = "dms-psc-subnet"
  region  = var.region
  project = var.project_id

  network = google_compute_network.psc_sp_network.id
  # CIDR range can be lower.
  ip_cidr_range = "10.0.0.0/16"
}

resource "google_compute_subnetwork" "psc_sp_nat" {
  provider = google-beta
  name     = "dms-psc-nat"
  region   = var.region
  project  = var.project_id

  network = google_compute_network.psc_sp_network.id
  purpose = "PRIVATE_SERVICE_CONNECT"
  # CIDR range can be lower.
  ip_cidr_range = "10.1.0.0/16"
}

resource "google_compute_service_attachment" "psc_sp_service_attachment" {
  provider = google-beta
  name     = "dms-psc-svc-att"
  region   = var.region
  project  = var.project_id

  enable_proxy_protocol = false
  connection_preference = "ACCEPT_MANUAL"
  nat_subnets           = [google_compute_subnetwork.psc_sp_nat.id]
  target_service        = google_compute_forwarding_rule.psc_sp_target_direct_rule.id
}

resource "google_compute_forwarding_rule" "psc_sp_target_direct_rule" {
  name       = "dms-psc-fr"
  region     = var.region
  project    = var.project_id
  network    = google_compute_network.psc_sp_network.id
  subnetwork = google_compute_subnetwork.psc_sp_subnetwork.id

  load_balancing_scheme = "INTERNAL"
  ip_protocol           = "TCP"
  all_ports             = true

  target = google_compute_target_instance.psc_sp_target.id

}

resource "google_compute_target_instance" "psc_sp_target" {
  provider = google-beta
  name     = "dms-psc-fr-target"
  zone     = var.zone
  instance = google_compute_instance.psc_sp_bastion.id
  network  = google_compute_network.psc_sp_network.id
}

resource "google_compute_instance" "psc_sp_bastion" {
  name           = "dms-psc-cloud-sql-bastion"
  project        = var.project_id
  machine_type   = "e2-medium"
  zone           = var.zone
  can_ip_forward = true

  boot_disk {
    initialize_params {
      image = "debian-cloud/debian-11"
    }
  }

  # The incoming NIC defines the default gateway which must be the Private Service Connect subnet.
  network_interface {
    network    = google_compute_network.psc_sp_network.id
    subnetwork = google_compute_subnetwork.psc_sp_subnetwork.id
  }

  # The outgoing NIC which is on the same network as the Cloud SQL instance.
  network_interface {
    network = data.google_compute_subnetwork.db_network_subnet.network
  }

  metadata_startup_script = <<SCRIPT

#!/bin/bash

# Route the private IP address of the database using the gateway of the database subnetwork.
# To find the gateway for the relevant subnetwork, go to the VPC network page
# in the Google Cloud console. Click VPC networks, and select the database VPC
# to see the details.
ip route add ${data.google_sql_database_instance.csql_instance.private_ip_address} \
via ${data.google_compute_subnetwork.db_network_subnet.gateway_address}

# Install Dante SOCKS server.
apt-get install -y dante-server

# Create the Dante configuration file.
touch /etc/danted.conf

# Create a proxy.log file.
touch proxy.log

# Add the following configuration for Dante:
cat > /etc/danted.conf << EOF
logoutput: /proxy.log
user.privileged: proxy
user.unprivileged: nobody

internal: 0.0.0.0 port = ${var.port}
external: ens5

clientmethod: none
socksmethod: none

client pass {
        from: 0.0.0.0/0
        to: 0.0.0.0/0
        log: connect error disconnect
}
client block {
        from: 0.0.0.0/0
        to: 0.0.0.0/0
        log: connect error
}
socks pass {
        from: 0.0.0.0/0
        to: ${data.google_sql_database_instance.csql_instance.private_ip_address}/32
        protocol: tcp
        log: connect error disconnect
}
socks block {
        from: 0.0.0.0/0
        to: 0.0.0.0/0
        log: connect error
}
EOF

# Start the Dante server.
systemctl restart danted

tail -f proxy.log

SCRIPT
}

# Required firewall rules:

/* Firewall rule allowing the Private Service Connect NAT subnet to access
the Private Service Connect subnet. */
resource "google_compute_firewall" "psc_sp_in_fw" {
  name    = "dms-psc-ingress-nat-fw"
  project = var.project_id
  network = google_compute_network.psc_sp_network.id

  log_config {
    metadata = "INCLUDE_ALL_METADATA"
  }

  allow {
    protocol = "all"
  }

  priority  = 1000
  direction = "INGRESS"
  source_ranges = [google_compute_subnetwork.psc_sp_nat.ip_cidr_range]
}

/* The router that the bastion VM uses to install external packages
(for example, Dante SOCKS server). */

resource "google_compute_router" "psc_sp_ex_router" {
  name    = "dms-psc-external-router"
  project = var.project_id
  region  = var.region
  network = google_compute_network.psc_sp_network.id
}

resource "google_compute_router_nat" "psc_sp_ex_router_nat" {
  name    = "dms-psc-external-router-nat"
  project = var.project_id
  region  = var.region
  router  = google_compute_router.psc_sp_ex_router.name

  nat_ip_allocate_option             = "AUTO_ONLY"
  source_subnetwork_ip_ranges_to_nat = "ALL_SUBNETWORKS_ALL_IP_RANGES"

  log_config {
    enable = true
    filter = "ERRORS_ONLY"
  }
}

# The Private Service Connect service attachment.
output "service_attachment" {
  value = google_compute_service_attachment.psc_sp_service_attachment.id
}