Terraform bug

The template

resource "aws_route_table" "private" {
  vpc_id = "${aws_vpc.default.id}"
  route {
    cidr_block = "0.0.0.0/0"
    instance_id = "${aws_instance.nat.id}"
  }
  route {
    cidr_block = "10.0.0.0/16"
    gateway_id = "pcx-abcd"
  }
  tags { Name = "${concat(\"rtb-private-\",var.region_name)}" }
}

Apply

$ terraform apply

Updates terraform.tfstate with the below:

"aws_route_table.private": {
    "type": "aws_route_table",
    "depends_on": [
        "aws_vpc.default",
        "aws_instance.nat"
    ],
    "primary": {
        "id": "rtb-cfd9b9aa",
        "attributes": {
            "id": "rtb-cfd9b9aa",
            "route.#": "2",
            "route.1790308496.cidr_block": "10.0.0.0/16",
            "route.3119882668.cidr_block": "0.0.0.0/0",
            "route.3119882668.instance_id": "i-460975aa",
            "tags.Name": "rtb-private-virginia",
            "vpc_id": "vpc-abc"
        }
    }
}

Refresh

  $ terraform refresh

No Updates terraform.tfstate, it remains:

  "aws_route_table.private": {
      "type": "aws_route_table",
      "depends_on": [
          "aws_vpc.default",
          "aws_instance.nat"
      ],
      "primary": {
          "id": "rtb-cfd9b9aa",
          "attributes": {
              "id": "rtb-cfd9b9aa",
              "route.#": "2",
              "route.1790308496.cidr_block": "10.0.0.0/16",
              "route.3119882668.cidr_block": "0.0.0.0/0",
              "route.3119882668.instance_id": "i-460975aa",
              "tags.Name": "rtb-private-virginia",
              "vpc_id": "vpc-abc"
          }
      }
  },

Plan

Plan suggests modifications, even though there are no modifications

$ terraform plan -module-depth=1

...
~ module.primary-services.aws_route_table.private
route.3810732900.cidr_block:  "" => "0.0.0.0/0"
route.3810732900.gateway_id:  "" => ""
route.3810732900.instance_id: "" => "i-460975aa"
route.3996912366.cidr_block:  "" => "10.0.0.0/16"
route.3996912366.gateway_id:  "" => "pcx-abcd"
route.3996912366.instance_id: "" => ""

The state file remains the same

Apply

Apply makes the updates

$ terraform apply

...
module.primary-services.aws_route_table.private: Modifying...
  route.3810732900.cidr_block:  "" => "0.0.0.0/0"
  route.3810732900.gateway_id:  "" => ""
  route.3810732900.instance_id: "" => "i-460975aa"
  route.3996912366.cidr_block:  "" => "10.0.0.0/16"
  route.3996912366.gateway_id:  "" => "pcx-abcd"
  route.3996912366.instance_id: "" => ""
module.primary-services.aws_route_table.private: Modifications complete
...

terraform.tfstate updated with below:

"aws_route_table.private": {
    "type": "aws_route_table",
    "depends_on": [
        "aws_vpc.default",
        "aws_instance.nat"
    ],
    "primary": {
        "id": "rtb-cfd9b9aa",
        "attributes": {
            "id": "rtb-cfd9b9aa",
            "route.#": "4",
            "route.1790308496.cidr_block": "10.0.0.0/16",
            "route.3119882668.cidr_block": "0.0.0.0/0",
            "route.3119882668.instance_id": "i-460975aa",
            "route.3810732900.cidr_block": "0.0.0.0/0",
            "route.3810732900.gateway_id": "",
            "route.3810732900.instance_id": "i-460975aa",
            "route.3996912366.cidr_block": "10.0.0.0/16",
            "route.3996912366.gateway_id": "pcx-abcd",
            "route.3996912366.instance_id": "",
            "tags.Name": "rtb-private-virginia",
            "vpc_id": "vpc-abc"
        }
    }
}