resource/aws_default_route_table: Fixes for creation and recreation b…

…ehavior when Default Route Table is missing (#10981)

Reference: #398
Reference: #3551
Reference: #9009

Previously on creation, if the Default Route Table was incorrectly configured or non-existent, the resource would unexpectedly attempt to remove itself from the Terraform state and propose recreation immediately. Prior to Terraform 0.12, this behavior was errantly acceptable. In Terraform 0.12, resources are required to return Terraform state about themselves during creation or throw an error explaining why the creation failed.

Previously on read, if the Default Route Table was missing (e.g. due to the VPC being deleted outside Terraform), the resource would return an error and require operators to manually perform a `terraform state rm` command instead of proposing resource recreation.

Output from new acceptance testing before code updates:

```
--- FAIL: TestAccAWSDefaultRouteTable_basic (20.02s)
    testing.go:628: Step 0, expected error:

        errors during apply: Provider produced inconsistent result after apply: When applying changes to aws_default_route_table.foo, provider "aws" produced an unexpected new value for was present, but now absent.

        This is a bug in the provider, which should be reported in the provider's own issue tracker.

        To match:

        TBD

--- FAIL: TestAccAWSDefaultRouteTable_disappears_Vpc (20.27s)
    testing.go:635: Step 0 error: errors during follow-up refresh:

        Error: Default Route table not found

    testing.go:696: Error destroying resource! WARNING: Dangling resources
        may exist. The full state and error is shown below.

        Error: errors during refresh: Default Route table not found

        State: <nil>
```

Output from acceptance testing after code updates:

```
--- PASS: TestAccAWSDefaultRouteTable_disappears_Vpc (20.46s)
--- PASS: TestAccAWSDefaultRouteTable_basic (40.99s)
--- PASS: TestAccAWSDefaultRouteTable_vpc_endpoint (49.71s)
--- PASS: TestAccAWSDefaultRouteTable_swap (73.89s)
--- PASS: TestAccAWSDefaultRouteTable_Route (87.09s)
--- PASS: TestAccAWSDefaultRouteTable_Route_TransitGatewayID (374.87s)
```

aws/resource_aws_default_route_table.go

@@ -107,12 +107,10 @@ func resourceAwsDefaultRouteTableCreate(d *schema.ResourceData, meta interface{}
 	conn := meta.(*AWSClient).ec2conn
 	rtRaw, _, err := resourceAwsRouteTableStateRefreshFunc(conn, d.Id())()
 	if err != nil {
-		return err
+		return fmt.Errorf("error reading EC2 Default Route Table (%s): %s", d.Id(), err)
 	}
 	if rtRaw == nil {
-		log.Printf("[WARN] Default Route Table not found")
-		d.SetId("")
-		return nil
+		return fmt.Errorf("error reading EC2 Default Route Table (%s): not found", d.Id())
 	}
 
 	rt := rtRaw.(*ec2.RouteTable)
@@ -151,7 +149,9 @@ func resourceAwsDefaultRouteTableRead(d *schema.ResourceData, meta interface{})
 	}
 
 	if len(resp.RouteTables) < 1 || resp.RouteTables[0] == nil {
-		return fmt.Errorf("Default Route table not found")
+		log.Printf("[WARN] EC2 Default Route Table (%s) not found, removing from state", d.Id())
+		d.SetId("")
+		return nil
 	}
 
 	rt := resp.RouteTables[0]

aws/resource_aws_default_route_table_test.go

@@ -2,6 +2,7 @@ package aws
 
 import (
 	"fmt"
+	"regexp"
 	"testing"
 
 	"github.com/aws/aws-sdk-go/aws"
@@ -12,6 +13,65 @@ import (
 )
 
 func TestAccAWSDefaultRouteTable_basic(t *testing.T) {
+	var routeTable1 ec2.RouteTable
+	resourceName := "aws_default_route_table.test"
+	vpcResourceName := "aws_vpc.test"
+
+	resource.ParallelTest(t, resource.TestCase{
+		PreCheck:     func() { testAccPreCheck(t) },
+		Providers:    testAccProviders,
+		CheckDestroy: testAccCheckRouteTableDestroy,
+		Steps: []resource.TestStep{
+			// Verify non-existent Route Table ID behavior
+			{
+				Config:      testAccDefaultRouteTableConfigDefaultRouteTableId("rtb-00000000"),
+				ExpectError: regexp.MustCompile(`EC2 Default Route Table \(rtb-00000000\): not found`),
+			},
+			// Verify invalid Route Table ID behavior
+			{
+				Config:      testAccDefaultRouteTableConfigDefaultRouteTableId("vpc-00000000"),
+				ExpectError: regexp.MustCompile(`EC2 Default Route Table \(vpc-00000000\): not found`),
+			},
+			{
+				Config: testAccDefaultRouteTableConfigRequired(),
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckRouteTableExists(resourceName, &routeTable1),
+					testAccCheckResourceAttrAccountID(resourceName, "owner_id"),
+					resource.TestCheckResourceAttr(resourceName, "propagating_vgws.#", "0"),
+					resource.TestCheckResourceAttr(resourceName, "route.#", "0"),
+					resource.TestCheckResourceAttr(resourceName, "tags.%", "0"),
+					resource.TestCheckResourceAttrPair(resourceName, "vpc_id", vpcResourceName, "id"),
+				),
+			},
+		},
+	})
+}
+
+func TestAccAWSDefaultRouteTable_disappears_Vpc(t *testing.T) {
+	var routeTable1 ec2.RouteTable
+	var vpc1 ec2.Vpc
+	resourceName := "aws_default_route_table.test"
+	vpcResourceName := "aws_vpc.test"
+
+	resource.ParallelTest(t, resource.TestCase{
+		PreCheck:     func() { testAccPreCheck(t) },
+		Providers:    testAccProviders,
+		CheckDestroy: testAccCheckRouteTableDestroy,
+		Steps: []resource.TestStep{
+			{
+				Config: testAccDefaultRouteTableConfigRequired(),
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckRouteTableExists(resourceName, &routeTable1),
+					testAccCheckVpcExists(vpcResourceName, &vpc1),
+					testAccCheckVpcDisappears(&vpc1),
+				),
+				ExpectNonEmptyPlan: true,
+			},
+		},
+	})
+}
+
+func TestAccAWSDefaultRouteTable_Route(t *testing.T) {
 	var v ec2.RouteTable
 
 	resource.ParallelTest(t, resource.TestCase{
@@ -153,6 +213,26 @@ func testAccCheckDefaultRouteTableDestroy(s *terraform.State) error {
 	return nil
 }
 
+func testAccDefaultRouteTableConfigDefaultRouteTableId(defaultRouteTableId string) string {
+	return fmt.Sprintf(`
+resource "aws_default_route_table" "test" {
+  default_route_table_id = %[1]q
+}
+`, defaultRouteTableId)
+}
+
+func testAccDefaultRouteTableConfigRequired() string {
+	return fmt.Sprintf(`
+resource "aws_vpc" "test" {
+  cidr_block = "10.1.0.0/16"
+}
+
+resource "aws_default_route_table" "test" {
+  default_route_table_id = aws_vpc.test.default_route_table_id
+}
+`)
+}
+
 const testAccDefaultRouteTableConfig = `
 resource "aws_vpc" "foo" {
   cidr_block           = "10.1.0.0/16"