How to Import an AWS Subnet into Terraform

Import AWS Subnet with Terraback (recommended)

Terraback reverse-engineers your live infrastructure: it reads the Amazon VPC resource with read-only credentials, generates the HCL, and produces the exact import block. Two commands take you from a live AWS Subnet to managed Terraform.

terraback scan all aws --region us-east-1

terraback aws import --method bulk

The Terraform import block

Terraback emits a Terraform 1.5+ import block like the one below. Because the block lives in your configuration, the import is reviewable in a pull request and repeatable across environments.

import {
  to = aws_subnet.public_a
  id = "subnet-0bb1c79de3a1b2c3d"
}

Example aws_subnet configuration

Here is a realistic AWS Subnet block. Terraback generates a fuller version from your actual resource attributes; this is a minimal, valid starting point.

resource "aws_subnet" "public_a" {
  vpc_id            = "vpc-0a1b2c3d4e5f6a7b8"
  cidr_block        = "10.0.1.0/24"
  availability_zone = "us-east-1a"

  tags = {
    Name = "public-a"
  }
}

Gotchas when importing a AWS Subnet

• map_public_ip_on_launch defaults to false in Terraform but may be true in the console; set it explicitly to avoid a diff.
• Route table associations are a separate aws_route_table_association resource and are not imported with the subnet.
• For IPv6 subnets, copy ipv6_cidr_block and assign_ipv6_address_on_creation exactly.

Doing it manually with terraform import

The native approach is to write the aws_subnet block by hand, then run terraform import aws_subnet.example <import-id> for every resource, one at a time. That works for a handful of resources, but it does not scale: you author all the HCL yourself and repeat the command for each item. Terraback generates the HCL and the import blocks for your whole account in one pass.

Import other AWS resources