Azure VPN Gateway OpenVPN

main.tf

resource "random_string" "random" {
  length = 8
  special = false
  upper = false
  number = false
}

resource "azurerm_public_ip" "vpn_ip" {
  name                = "vpn-ip"
  location            = var.region
  resource_group_name = var.resource_group_name

  domain_name_label = random_string.random.result
  

  allocation_method = "Dynamic"
  tags     = var.tags
}


resource "tls_private_key" "example" {
  algorithm = "RSA"
  rsa_bits  = "2048"
}

# Create the root certificate
resource "tls_self_signed_cert" "ca" {
  key_algorithm   = tls_private_key.example.algorithm
  private_key_pem = tls_private_key.example.private_key_pem

  # Certificate expires after 1 year
  validity_period_hours = 8766 

  # Generate a new certificate if Terraform is run within three
  # hours of the certificate's expiration time.
  early_renewal_hours = 200

  # Allow to be used as a CA
  is_ca_certificate = true

  allowed_uses = [
    "key_encipherment",
    "digital_signature",
    "server_auth",
    "client_auth",
    "cert_signing"
  ]

  dns_names = [ azurerm_public_ip.vpn_ip.domain_name_label ]

  subject {
      common_name  = "CAOpenVPN"
      organization = "dev env"
  }
}

resource "local_file" "ca_pem" {
  filename = "caCert.pem"
  content  = tls_self_signed_cert.ca.cert_pem
}

resource "null_resource" "cert_encode" {
  provisioner "local-exec" {
    # Bootstrap script called with private_ip of each node in the clutser
    command = "openssl x509 -in caCert.pem -outform der | base64 -w0 > caCert.der"
  }

  depends_on =  [ local_file.ca_pem ]
}

data "local_file" "ca_der" {
  filename = "caCert.der"

  depends_on = [
    null_resource.cert_encode
  ]
}

resource "tls_private_key" "client_cert" {
  algorithm = "RSA"
  rsa_bits  = "2048"
}

resource "tls_cert_request" "client_cert" {
  key_algorithm = tls_private_key.client_cert.algorithm
  private_key_pem = tls_private_key.client_cert.private_key_pem

  # dns_names = [ azurerm_public_ip.vpn_ip.domain_name_label ]

  subject {
      common_name  = "ClientOpenVPN"
      organization = "dev env"
  }
}

resource "tls_locally_signed_cert" "client_cert" {
  cert_request_pem = tls_cert_request.client_cert.cert_request_pem

  ca_key_algorithm = tls_private_key.client_cert.algorithm
  ca_private_key_pem = tls_private_key.client_cert.private_key_pem
  ca_cert_pem = tls_self_signed_cert.ca.cert_pem

  validity_period_hours = 43800

  allowed_uses = [
    "key_encipherment",
    "digital_signature",
    "server_auth",
    "key_encipherment",
    "client_auth",
  ]
}

resource "azurerm_virtual_network_gateway" "vpn-gateway" {
  name                = "vpn-gateway"
  location            = var.region
  resource_group_name = var.resource_group_name

  type = "Vpn"

  active_active = false
  enable_bgp    = false
  sku           = "VpnGw1"

  ip_configuration {
    name                          = "vnetGatewayConfig"
    public_ip_address_id          = azurerm_public_ip.vpn_ip.id
    private_ip_address_allocation = "Dynamic"
    subnet_id                     = azurerm_subnet.yoursubnethere.id
  }

  vpn_client_configuration {
    address_space = ["10.1.0.0/16"]

    vpn_client_protocols = ["OpenVPN"]
        root_certificate {
            name = "terraformselfsignedder"

            public_cert_data = data.local_file.ca_der.content
        }
  }


}

output "client_cert" {
  value = tls_locally_signed_cert.client_cert.cert_pem
}


output "client_key" {
  value = tls_private_key.client_cert.private_key_pem
}

output "vpn_id" {
  value = azurerm_virtual_network_gateway.vpn-gateway.id
}

openvpn_gen.sh

#!/bin/bash
set -e

# Get vars from TF State
VPN_ID=`terraform output vpn_id`
VPN_CLIENT_CERT=`terraform output client_cert`
VPN_CLIENT_KEY=`terraform output client_key`

# Replace newlines with \n so sed doesn't break
VPN_CLIENT_CERT="${VPN_CLIENT_CERT//$'\n'/\\n}"
VPN_CLIENT_KEY="${VPN_CLIENT_KEY//$'\n'/\\n}"

CONFIG_URL=`az network vnet-gateway vpn-client generate --ids $VPN_ID -o tsv`
wget $CONFIG_URL -O "vpnconfig.zip"
# Ignore complaint about backslash in filepaths
unzip -o "vpnconfig.zip" -d "./vpnconftemp"|| true
OPENVPN_CONFIG_FILE="./vpnconftemp/OpenVPN/vpnconfig.ovpn"

echo "Updating file $OPENVPN_CONFIG_FILE"

sed -i "s~\$CLIENTCERTIFICATE~$VPN_CLIENT_CERT~" $OPENVPN_CONFIG_FILE
sed -i "s~\$PRIVATEKEY~$VPN_CLIENT_KEY~g" $OPENVPN_CONFIG_FILE

cp $OPENVPN_CONFIG_FILE openvpn.ovpn

rm -r ./vpnconftemp
rm vpnconfig.zip