[Bug]: Route table updating all the time whenever applying Terraform configuration changes

[krishanshamod]

Terraform Core Version

1.3.7

AWS Provider Version

4.38.0

Affected Resource(s)

aws_route_table

Expected Behavior

I'm using a NAT instance instead of a NAT gateway and I configured the route in the private route table using Terraform. All works fine.

Actual Behavior

But when I'm applying any kind of Terraform change, it's suggesting route table updates.

Relevant Error/Panic Output Snippet

# aws_route_table.private_route_table will be updated in-place
  ~ resource "aws_route_table" "private_route_table" {
        id               = "rtb-xxxxxxxxxxxx"
      ~ route            = [
          + {
              + carrier_gateway_id         = ""
              + cidr_block                 = "0.0.0.0/0"
              + core_network_arn           = ""
              + destination_prefix_list_id = ""
              + egress_only_gateway_id     = ""
              + gateway_id                 = ""
              + instance_id                = ""
              + ipv6_cidr_block            = ""
              + local_gateway_id           = ""
              + nat_gateway_id             = ""
              + network_interface_id       = "eni-xxxxxxxxxxxx"
              + transit_gateway_id         = ""
              + vpc_endpoint_id            = ""
              + vpc_peering_connection_id  = ""
            },
          - {
              - carrier_gateway_id         = ""
              - cidr_block                 = "0.0.0.0/0"
              - core_network_arn           = ""
              - destination_prefix_list_id = ""
              - egress_only_gateway_id     = ""
              - gateway_id                 = ""
              - instance_id                = "i-xxxxxxxxxxxx"
              - ipv6_cidr_block            = ""
              - local_gateway_id           = ""
              - nat_gateway_id             = ""
              - network_interface_id       = "eni-xxxxxxxxxxxx"
              - transit_gateway_id         = ""
              - vpc_endpoint_id            = ""
              - vpc_peering_connection_id  = ""
            },
        ]
        tags             = {
            "Name" = "private_route_table"
        }
        # (5 unchanged attributes hidden)
    }

Terraform Configuration Files

resource "aws_route_table" "private_route_table" {
  vpc_id = aws_vpc.main.id

  route {
    cidr_block           = "0.0.0.0/0"
    network_interface_id = aws_instance.nat_vm.primary_network_interface_id
  }

  tags = {
    Name = "private_route_table"
  }
}

Steps to Reproduce

That problem will be fixed when I add instance_id to the route but that attribute is a deprecated one.

Here's the code after I added that attribute.

resource "aws_route_table" "private_route_table" {
  vpc_id = aws_vpc.main.id

  route {
    cidr_block           = "0.0.0.0/0"
    instance_id          = aws_instance.nat_vm.id
    network_interface_id = aws_instance.nat_vm.primary_network_interface_id
  }

  tags = {
    Name = "private_route_table"
  }
}

Debug Output

No response

Panic Output

No response

Important Factoids

No response

References

No response

Would you like to implement a fix?

None

[github-actions[bot]]

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[ssadler]

Any update on this? Is there a workaround?

[jrandall]

I believe this was fixed in https://github.com/hashicorp/terraform-provider-aws/pull/30804 and release in v5 of the provider.