# Deploy VPC Connection

## Application Scenario

Enterprise Router (ER) is a high-performance, highly available enterprise-grade router service provided by Huawei Cloud, supporting enterprise-level network functions such as multi-VPC interconnection, dedicated line access, and VPN connections. ER service provides flexible routing policies and rich network connectivity capabilities, meeting complex enterprise network architecture requirements.

ER VPC connections are a core function of the ER service, used to connect VPC networks to enterprise routers, implementing VPC interconnection and traffic routing. Through VPC connections, enterprises can build cross-VPC network architectures, implementing advanced network functions such as resource sharing, load balancing, and failover. This best practice will introduce how to use Terraform to automatically deploy VPC connections, including VPC creation, ER instance creation, and VPC connection configuration.

## Related Resources/Data Sources

This best practice involves the following main resources and data sources:

### Data Sources

* [ER Availability Zones Query Data Source (data.huaweicloud\_er\_availability\_zones)](https://registry.terraform.io/providers/huaweicloud/huaweicloud/latest/docs/data-sources/er_availability_zones)

### Resources

* [VPC Resource (huaweicloud\_vpc)](https://registry.terraform.io/providers/huaweicloud/huaweicloud/latest/docs/resources/vpc)
* [VPC Subnet Resource (huaweicloud\_vpc\_subnet)](https://registry.terraform.io/providers/huaweicloud/huaweicloud/latest/docs/resources/vpc_subnet)
* [ER Instance Resource (huaweicloud\_er\_instance)](https://registry.terraform.io/providers/huaweicloud/huaweicloud/latest/docs/resources/er_instance)
* [ER VPC Connection Resource (huaweicloud\_er\_vpc\_attachment)](https://registry.terraform.io/providers/huaweicloud/huaweicloud/latest/docs/resources/er_vpc_attachment)

### Resource/Data Source Dependencies

```
data.huaweicloud_er_availability_zones.test
    └── huaweicloud_er_instance.test

huaweicloud_vpc.test
    ├── huaweicloud_vpc_subnet.test
    │   └── huaweicloud_er_vpc_attachment.test
    └── huaweicloud_er_vpc_attachment.test

huaweicloud_er_instance.test
    └── huaweicloud_er_vpc_attachment.test
```

## Operation Steps

### 1. Script Preparation

Prepare the TF file (e.g., main.tf) in the specified workspace for writing the current best practice script, ensuring that it (or other TF files in the same directory) contains the provider version declaration and Huawei Cloud authentication information required for deploying resources. Refer to the "Preparation Before Deploying Huawei Cloud Resources" document for configuration introduction.

### 2. Query ER Availability Zone Information Through Data Source

Add the following script to the TF file (e.g., main.tf) to instruct Terraform to perform a data source query, the results of which are used to create ER instances:

```hcl
# Get all ER availability zone information under the specified region (if the region parameter is omitted, it defaults to the region specified in the current provider block), used to create ER instances
data "huaweicloud_er_availability_zones" "test" {}
```

**Parameter Description**:

* No additional parameters required, the data source will automatically get all ER availability zone information in the current region

### 3. Create VPC

Add the following script to the TF file (e.g., main.tf) to instruct Terraform to create a VPC resource:

```hcl
variable "vpc_name" {
  description = "VPC name"
  type        = string
}

variable "vpc_cidr" {
  description = "VPC CIDR block"
  type        = string
  default     = "192.168.0.0/16"
}

# Create a VPC resource under the specified region (if the region parameter is omitted, it defaults to the region specified in the current provider block)
resource "huaweicloud_vpc" "test" {
  name = var.vpc_name
  cidr = var.vpc_cidr
}
```

**Parameter Description**:

* **name**: VPC name, assigned by referencing the input variable vpc\_name
* **cidr**: VPC CIDR block, assigned by referencing the input variable vpc\_cidr

### 4. Create VPC Subnet

Add the following script to the TF file (e.g., main.tf) to instruct Terraform to create a VPC subnet resource:

```hcl
variable "subnet_name" {
  description = "VPC subnet name"
  type        = string
}

variable "subnet_cidr" {
  description = "VPC subnet CIDR block"
  type        = string
  default     = ""
}

variable "subnet_gateway_ip" {
  description = "VPC subnet gateway IP"
  type        = string
  default     = ""
}

# Create a VPC subnet resource under the specified region (if the region parameter is omitted, it defaults to the region specified in the current provider block)
resource "huaweicloud_vpc_subnet" "test" {
  vpc_id     = huaweicloud_vpc.test.id
  name       = var.subnet_name
  cidr       = var.subnet_cidr == "" ? cidrsubnet(huaweicloud_vpc.test.cidr, 8, 0) : var.subnet_cidr
  gateway_ip = var.subnet_gateway_ip == "" ? cidrhost(cidrsubnet(huaweicloud_vpc.test.cidr, 8, 0), 1) : var.subnet_gateway_ip
}
```

**Parameter Description**:

* **vpc\_id**: VPC ID, assigned by referencing the VPC resource (huaweicloud\_vpc.test) ID
* **name**: Subnet name, assigned by referencing the input variable subnet\_name
* **cidr**: Subnet CIDR block, prioritizes using input variable, calculates using cidrsubnet function if empty
* **gateway\_ip**: Gateway IP, prioritizes using input variable, calculates using cidrhost function if empty

### 5. Create ER Instance

Add the following script to the TF file (e.g., main.tf) to instruct Terraform to create an ER instance resource:

```hcl
variable "er_instance_name" {
  description = "ER instance name"
  type        = string
}

variable "er_instance_asn" {
  description = "ER instance ASN number"
  type        = number
}

# Create an ER instance resource under the specified region (if the region parameter is omitted, it defaults to the region specified in the current provider block)
resource "huaweicloud_er_instance" "test" {
  availability_zones = slice(data.huaweicloud_er_availability_zones.test.names, 0, 1)
  name               = var.er_instance_name
  asn                = var.er_instance_asn
}
```

**Parameter Description**:

* **availability\_zones**: Availability zone list, using the first result from ER availability zone list query data source
* **name**: Instance name, assigned by referencing the input variable er\_instance\_name
* **asn**: ASN number, assigned by referencing the input variable er\_instance\_asn

### 6. Create ER VPC Connection

Add the following script to the TF file (e.g., main.tf) to instruct Terraform to create an ER VPC connection resource:

```hcl
variable "er_vpc_attachment_name" {
  description = "ER VPC connection name"
  type        = string
}

variable "er_vpc_attachment_auto_create_vpc_routes" {
  description = "Whether to automatically create VPC routes"
  type        = bool
  default     = true
}

# Create an ER VPC connection resource under the specified region (if the region parameter is omitted, it defaults to the region specified in the current provider block)
resource "huaweicloud_er_vpc_attachment" "test" {
  instance_id = huaweicloud_er_instance.test.id
  vpc_id      = huaweicloud_vpc.test.id
  subnet_id   = huaweicloud_vpc_subnet.test.id

  name                   = var.er_vpc_attachment_name
  auto_create_vpc_routes = var.er_vpc_attachment_auto_create_vpc_routes
}
```

**Parameter Description**:

* **instance\_id**: ER instance ID, assigned by referencing the ER instance resource (huaweicloud\_er\_instance.test) ID
* **vpc\_id**: VPC ID, assigned by referencing the VPC resource (huaweicloud\_vpc.test) ID
* **subnet\_id**: Subnet ID, assigned by referencing the VPC subnet resource (huaweicloud\_vpc\_subnet.test) ID
* **name**: Connection name, assigned by referencing the input variable er\_vpc\_attachment\_name
* **auto\_create\_vpc\_routes**: Auto create VPC routes, assigned by referencing the input variable er\_vpc\_attachment\_auto\_create\_vpc\_routes

### 7. Preset Input Parameters Required for Resource Deployment (Optional)

In this practice, some resources and data sources use input variables to assign values to configuration content. These input parameters need to be manually entered during subsequent deployments. At the same time, Terraform provides a method to preset these configurations through `tfvars` files, which can avoid repeated input during each execution.

Create a `terraform.tfvars` file in the working directory with the following example content:

```hcl
# Authentication information
region_name = "cn-north-4"
access_key  = "your-access-key"
secret_key  = "your-secret-key"

# Network configuration
vpc_name    = "tf_test_er_instance_vpc"
vpc_cidr    = "192.168.0.0/16"
subnet_name = "tf_test_er_instance_subnet"

# ER instance configuration
er_instance_name = "tf_test_er_instance"
er_instance_asn  = 64512

# ER VPC connection configuration
er_vpc_attachment_name = "tf_test_er_vpc_attachment"
```

**Usage**:

1. Save the above content as `terraform.tfvars` file in the working directory (this file name allows users to automatically import the content of this `tfvars` file when executing terraform commands; for other names, `.auto` needs to be added before tfvars, such as `variables.auto.tfvars`)
2. Modify parameter values as needed
3. When executing `terraform plan` or `terraform apply`, Terraform will automatically read the variable values from this file

In addition to using `terraform.tfvars` file, variable values can also be set in the following ways:

1. Command line parameters: `terraform apply -var="vpc_name=my-vpc" -var="er_instance_name=my-er"`
2. Environment variables: `export TF_VAR_vpc_name=my-vpc`
3. Custom named variable files: `terraform apply -var-file="custom.tfvars"`

> Note: If the same variable is set in multiple ways, Terraform will use the variable value according to the following priority: command line parameters > variable files > environment variables > default values.

### 8. Initialize and Apply Terraform Configuration

After completing the above script configuration, execute the following steps to create resources:

1. Run `terraform init` to initialize the environment
2. Run `terraform plan` to view the resource creation plan
3. After confirming the resource plan is correct, run `terraform apply` to start creating VPC connections
4. Run `terraform show` to view the created VPC connections

## Reference Information

* [Huawei Cloud ER Product Documentation](https://support.huaweicloud.com/er/index.html)
* [Huawei Cloud Provider Documentation](https://registry.terraform.io/providers/huaweicloud/huaweicloud/latest/docs)
* [Best Practice Source Code Reference For ER VPC Connection](https://github.com/huaweicloud/terraform-provider-huaweicloud/tree/master/examples/er/vpc-attachment)