Move resources to another VPC

[bastiheart]

I have 2 VPCs in the OTC. Now I would like to use Terraform to move the resources from VPC A to VPC B. To do this, I have adjusted the VPC ID for resources from VPC B to the ID from VPC A in my Terraform scripts.
When I want to execute the script, what happens in the background? Are the resources moved completely?
The Terraform plan at least shows that the VPC ID is adjusted.

[anton-sidelnikov]

Hi @bastiheart, migration of the resources not that simple:
Terraform interprets this change as a modification to existing resources. Depending on the resource type, Terraform might do one of the following:

1. Recreate the Resource (Destroy + Create):
   Most network-related resources (like subnets, security groups, etc.) cannot just be “moved” to another VPC. When you change the vpc_id, Terraform will often show a -/+ plan, which means:
   • Destroy the existing resource in VPC A
   • Create a new resource in VPC B
     Important: This can result in downtime or data loss if not handled carefully.
2. Error or Unsupported Change:
   Some resources do not support changing the vpc_id in-place or even via recreation. Terraform may show an error or simply refuse to apply the plan unless you explicitly force it with tainting or create_before_destroy strategies.

Migration can be done through:

1. Create a new set of resources in VPC B manually or via Terraform, instead of modifying the VPC ID directly.
2. Migrate data/configurations (e.g., database contents, server images) from the old resources to the new ones.
3. Test everything in VPC B.
4. Once VPC B is fully operational, decommission the old resources in VPC A.
5. Optionally, refactor your Terraform scripts to reflect the new setup cleanly.