aws_route resource generates constant diff in terraform plan when specifying only the network_interface_id as a route target

[ttcl19]

Terraform Version

Terraform v0.13.5
AWS Provider version v3.22.0

Terraform Configuration Files

resource "aws_route_table" "aws_rtb" {
  vpc_id = module.foo_vpc.vpc_id
  tags = {
    Name = "rtb"
  }

  dynamic "route" {
    for_each = local.dhcp_route
    content {
      cidr_block                = route.key // This is a CIDR string
      egress_only_gateway_id    = ""
      gateway_id                = ""
      local_gateway_id          = ""
      ipv6_cidr_block           = ""
      nat_gateway_id            = ""
      network_interface_id      = route.value[1] // This is a string in a list
      transit_gateway_id        = ""
      vpc_peering_connection_id = ""
      vpc_endpoint_id           = ""
    }
  }

Debug Output

      + {
          + cidr_block                = "172.30.92.0/24"
          + egress_only_gateway_id    = ""
          + gateway_id                = ""
          + instance_id               = ""
          + ipv6_cidr_block           = ""
          + local_gateway_id          = ""
          + nat_gateway_id            = ""
          + network_interface_id      = "eni-1234"
          + transit_gateway_id        = ""
          + vpc_endpoint_id           = ""
          + vpc_peering_connection_id = ""
        },
      - {
          - cidr_block                = "172.30.92.0/24"
          - egress_only_gateway_id    = ""
          - gateway_id                = ""
          - instance_id               = "i-5678"
          - ipv6_cidr_block           = ""
          - local_gateway_id          = ""
          - nat_gateway_id            = ""
          - network_interface_id      = "eni-1234"
          - transit_gateway_id        = ""
          - vpc_endpoint_id           = ""
          - vpc_peering_connection_id = ""
        },

Expected Behavior

No diff for existing routes.

And being able to push a new route with network_interface_id as a target, either by specifying both the instance_id AND the network_interface_id, or only the network_interface_id but without it creating diffs afterwards in terraform plan (due to not specifying instance_id)

Actual Behavior

We see a permanent diff for existing routes because the instance ID isn't in the configuration, but we can't explicitly set the instance_id because only one of instance_id or network_interface_id can be set for terraform apply.

Steps to Reproduce

Create an aws_route resource with route config blocks.

[ghost]

This issue has been automatically migrated to hashicorp/terraform-provider-aws#16999 because it looks like an issue with that provider. If you believe this is not an issue with the provider, please reply to hashicorp/terraform-provider-aws#16999.

[ghost]

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