How to Import an AWS Transit Gateway Route Table Propagation into Terraform

Import AWS Transit Gateway Route Table Propagation with Terraback (recommended)

Terraback reverse-engineers your live infrastructure: it reads the Amazon VPC Transit Gateway resource with read-only credentials, generates the HCL, and produces the exact import block. Two commands take you from a live AWS Transit Gateway Route Table Propagation 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_ec2_transit_gateway_route_table_propagation.example
  id = "tgw-rtb-12345678_tgw-attach-87654321"
}

Example aws_ec2_transit_gateway_route_table_propagation configuration

Here is a realistic AWS Transit Gateway Route Table Propagation block. Terraback generates a fuller version from your actual resource attributes; this is a minimal, valid starting point.

resource "aws_ec2_transit_gateway_route_table_propagation" "example" {
  transit_gateway_attachment_id  = "tgw-attach-87654321"
  transit_gateway_route_table_id = "tgw-rtb-12345678"
}

Gotchas when importing a AWS Transit Gateway Route Table Propagation

• Propagation makes an attachment's routes appear in a route table; the composite import ID joins the route table ID and attachment ID with an underscore, and both parent resources must already be in state.
• Propagation and association are different concepts and use the same ID shape, so be careful to import each into the correct resource type or routing will look wrong.
• Routes added by propagation are dynamic and must not also be defined as static aws_ec2_transit_gateway_route entries for the same CIDR, or the two will fight.
• transit_gateway_attachment_id and transit_gateway_route_table_id are force-new; editing either re-creates the propagation and momentarily withdraws the propagated routes.

Doing it manually with terraform import

The native approach is to write the aws_ec2_transit_gateway_route_table_propagation block by hand, then run terraform import aws_ec2_transit_gateway_route_table_propagation.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