Error "Unable to check for presence of an existing transit gateway attachment" when creating an HVN attachment using Terraform

Introduction

Customers can choose to create HVN and TGW attachments using Terraform Provider. For additional details, check Terraform Provider (hcp_aws_transit_gateway_attachment (Resource). 

Problem

When trying to create resources such as HVN and TGW attachments, using Terraform Provider, the following error appears:

Error: unable to check for presence of an existing transit gateway attachment (example-tgw-attachment): [GET /network/2020-09-07/organizations/{hvn.location.organizationid}/projects/{hvn.location.projectid}/networks/{hvn.id}/transit-gateway-attachments/{id}][500] GetTGWAttachment default &{Code:13 Details:[] Error: Message:}
│
│ with hcpawstransitgatewayattachment.example,
│ on main.tf line 51, in resource "hcpawstransitgatewayattachment" "example":
│ 51: resource "hcpawstransitgatewayattachment" "example" {

Cause

The error appears due to using the same project_id & transit_gateway_attachment_idin the Terraform Plan for the subsequent creation of resources under the same HCP Project, since the TGW attachment ID is being created in the below format:

"id": "/project/<PROJECT_ID>/hashicorp.network.tgw-attachment/<transit_gateway_attachment_id>",

Solution

There are a couple of solutions, which are outlined below:

1. Change the TGW attachment ID (transit_gateway_attachment_id) to not overlap with an existing one in the project.

2. Deploy resources in a different HCP Project altogether. When choosing this option, it's not necessary to change the attachment_id as mentioned in the solution above.