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Routing through a NAT instance using Terraform

Written by
Updated at May 7, 2025

To set up routing through a NAT instance using Terraform:

  1. Get your cloud ready.
  2. Create an infrastructure.
  3. Test the NAT instance.

If you no longer need the resources you created, delete them.

Getting started

Sign up in Yandex Cloud and create a billing account:

  1. Navigate to the management console and log in to Yandex Cloud or register a new account.
  2. On the Yandex Cloud Billing page, make sure you have a billing account linked and it has the ACTIVE or TRIAL_ACTIVE status. If you do not have a billing account, create one and link a cloud to it.

If you have an active billing account, you can navigate to the cloud page to create or select a folder for your infrastructure to operate in.

Learn more about clouds and folders.

The cost of NAT instance support includes:

Create an infrastructure

With Terraform, you can quickly create a cloud infrastructure in Yandex Cloud and manage it using configuration files. These files store the infrastructure description written in HashiCorp Configuration Language (HCL). If you change the configuration files, Terraform automatically detects which part of your configuration is already deployed, and what should be added or removed.

Terraform is distributed under the Business Source License. The Yandex Cloud provider for Terraform is distributed under the MPL-2.0 license.

For more information about the provider resources, see the documentation on the Terraform website or mirror website.

To create an infrastructure using Terraform:

  1. Install Terraform, get the authentication credentials, and specify the source for installing the Yandex Cloud provider (see Configure a provider, step 1).

  2. Prepare the infrastructure description file:

    1. Clone the repository with configuration files:

      git clone https://github.com/yandex-cloud-examples/yc-compute-nat-instance.git

    2. Navigate to the repository directory. Make sure it contains the following files:

      • nat-instance.tf: New infrastructure configuration.
      • nat-instance.auto.tfvars: User data.

    1. Create a folder for the infrastructure description file.

    2. Create a configuration file named nat-instance.tf in the folder:

      nat-instance.tf
      # Declaring variables for custom parameters

variable "folder_id" {
  type = string
}

variable "vm_user" {
  type = string
}

variable "vm_user_nat" {
  type = string
}

variable "ssh_key_path" {
  type = string
}

# Adding other variables

locals {
  network_name     = "my-vpc"
  subnet_name1     = "public-subnet"
  subnet_name2     = "private-subnet"
  sg_nat_name      = "nat-instance-sg"
  vm_test_name     = "test-vm"
  vm_nat_name      = "nat-instance"
  route_table_name = "nat-instance-route"
}

# Configuring a provider

terraform {
  required_providers {
    yandex = {
      source  = "yandex-cloud/yandex"
      version = ">= 0.47.0"
    }
  }
}

provider "yandex" {
  folder_id = var.folder_id
}

# Creating a cloud network

resource "yandex_vpc_network" "my-vpc" {
  name = local.network_name
}

# Creating subnets

resource "yandex_vpc_subnet" "public-subnet" {
  name           = local.subnet_name1
  zone           = "ru-central1-a"
  network_id     = yandex_vpc_network.my-vpc.id
  v4_cidr_blocks = ["192.168.1.0/24"]
}

resource "yandex_vpc_subnet" "private-subnet" {
  name           = local.subnet_name2
  zone           = "ru-central1-a"
  network_id     = yandex_vpc_network.my-vpc.id
  v4_cidr_blocks = ["192.168.2.0/24"]
  route_table_id = yandex_vpc_route_table.nat-instance-route.id
}

# Creating a security group

resource "yandex_vpc_security_group" "nat-instance-sg" {
  name       = local.sg_nat_name
  network_id = yandex_vpc_network.my-vpc.id

  egress {
    protocol       = "ANY"
    description    = "any"
    v4_cidr_blocks = ["0.0.0.0/0"]
  }

  ingress {
    protocol       = "TCP"
    description    = "ssh"
    v4_cidr_blocks = ["0.0.0.0/0"]
    port           = 22
  }

  ingress {
    protocol       = "TCP"
    description    = "ext-http"
    v4_cidr_blocks = ["0.0.0.0/0"]
    port           = 80
  }

  ingress {
    protocol       = "TCP"
    description    = "ext-https"
    v4_cidr_blocks = ["0.0.0.0/0"]
    port           = 443
  }
}

# Adding a prebuilt VM image

resource "yandex_compute_image" "ubuntu-1804-lts" {
  source_family = "ubuntu-1804-lts"
}

resource "yandex_compute_image" "nat-instance-ubuntu" {
  source_family = "nat-instance-ubuntu"
}

# Creating boot disks

resource "yandex_compute_disk" "boot-disk-ubuntu" {
  name     = "boot-disk-ubuntu"
  type     = "network-hdd"
  zone     = "ru-central1-a"
  size     = "20"
  image_id = yandex_compute_image.ubuntu-1804-lts.id
}

resource "yandex_compute_disk" "boot-disk-nat" {
  name     = "boot-disk-nat"
  type     = "network-hdd"
  zone     = "ru-central1-a"
  size     = "20"
  image_id = yandex_compute_image.nat-instance-ubuntu.id
}

# Creating a VM instance

resource "yandex_compute_instance" "test-vm" {
  name        = local.vm_test_name
  platform_id = "standard-v3"
  zone        = "ru-central1-a"

  resources {
    core_fraction = 20
    cores         = 2
    memory        = 2
  }

  boot_disk {
    disk_id = yandex_compute_disk.boot-disk-ubuntu.id
  }

  network_interface {
    subnet_id          = yandex_vpc_subnet.private-subnet.id
    security_group_ids = [yandex_vpc_security_group.nat-instance-sg.id]
  }

  metadata = {
    user-data = "#cloud-config\nusers:\n  - name: ${var.vm_user}\n    groups: sudo\n    shell: /bin/bash\n    sudo: 'ALL=(ALL) NOPASSWD:ALL'\n    ssh_authorized_keys:\n      - ${file("${var.ssh_key_path}")}"
  }
}

# Creating an NAT instance

resource "yandex_compute_instance" "nat-instance" {
  name        = local.vm_nat_name
  platform_id = "standard-v3"
  zone        = "ru-central1-a"

  resources {
    core_fraction = 20
    cores         = 2
    memory        = 2
  }

  boot_disk {
    disk_id = yandex_compute_disk.boot-disk-nat.id
  }

  network_interface {
    subnet_id          = yandex_vpc_subnet.public-subnet.id
    security_group_ids = [yandex_vpc_security_group.nat-instance-sg.id]
    nat                = true
  }

  metadata = {
    user-data = "#cloud-config\nusers:\n  - name: ${var.vm_user_nat}\n    groups: sudo\n    shell: /bin/bash\n    sudo: 'ALL=(ALL) NOPASSWD:ALL'\n    ssh_authorized_keys:\n      - ${file("${var.ssh_key_path}")}"
  }
}

# Creating a route table and static route

resource "yandex_vpc_route_table" "nat-instance-route" {
  name       = "nat-instance-route"
  network_id = yandex_vpc_network.my-vpc.id
  static_route {
    destination_prefix = "0.0.0.0/0"
    next_hop_address   = yandex_compute_instance.nat-instance.network_interface.0.ip_address
  }
}

    3. In the folder, create a user data file named nat-instance.auto.tfvars:

      nat-instance.auto.tfvars
      folder_id    = "<folder_ID>"
vm_user      = "<VM_username>"
vm_user_nat  = "<NAT_instance_username>"
ssh_key_path = "<path_to_public_SSH_key>"

    Learn more about the properties of Terraform resources in the provider documentation:

  3. In the nat-instance.auto.tfvars file, set the following user-defined properties:

    • folder_id: Folder ID.
    • vm_user: VM user name.
    • vm_user_nat: NAT instance user name.
    • ssh_key_path: Path to the file with a public SSH key to authenticate the user on the VM. For more information, see Creating an SSH key pair.

  4. Create resources:

    1. In the terminal, change to the folder where you edited the configuration file.

    2. Make sure the configuration file is correct using the command:

      terraform validate

      If the configuration is correct, the following message is returned:

      Success! The configuration is valid.

    3. Run the command:

      terraform plan

      The terminal will display a list of resources with parameters. No changes are made at this step. If the configuration contains errors, Terraform will point them out.

    4. Apply the configuration changes:

      terraform apply

    5. Confirm the changes: type yes in the terminal and press Enter.

Test the NAT instance

  1. Connect to the VM via a private IP address, using the NAT instance as a jump host:

    ssh -J <NAT_instance_username>@<NAT_instance_public_IP_address> \
  <VM_user_name>@<VM_internal_IP_address>

    You can also connect to the test VM using the standard input/output redirection (-W flag) to forward the connection through a NAT instance:

    ssh -o ProxyCommand="ssh -i <NAT_key_file_path/name> -W %h:%p <NAT_username>@<NAT_public_IP_address>" \
  -i <VM_key_file_path/name> <VM_user_name>@<VM_internal_IP_address>

    Use this command for connection in the following cases:

    • Your VM is running an OpenSSH version below 7.3.
    • Your SSH keys are stored outside the default directory or have non-standard names.

  2. Type yes to connect to the NAT instance and re-enter yes to connect to the test VM.

    Note

    When you type yes, the command may not be displayed in the terminal, but it will run anyway.

  3. Make sure the test VM is connected to the internet via the public IP address of the NAT instance. Run this command:

    curl ifconfig.co

    If it returns the public IP address of the NAT instance, the configuration is correct.

How to delete the resources you created

To shut down the NAT instance and stop paying for the created resources:

  1. Open the nat-instance.tf configuration file and delete the description of the new infrastructure from it.

  2. Apply the changes:

    1. In the terminal, change to the folder where you edited the configuration file.

    2. Make sure the configuration file is correct using the command:

      terraform validate

      If the configuration is correct, the following message is returned:

      Success! The configuration is valid.

    3. Run the command:

      terraform plan

      The terminal will display a list of resources with parameters. No changes are made at this step. If the configuration contains errors, Terraform will point them out.

    4. Apply the configuration changes:

      terraform apply

    5. Confirm the changes: type yes in the terminal and press Enter.

See also

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