vpc/route_table: Allow local inline routes

.changelog/32794.txt

@@ -0,0 +1,3 @@
+```release-note:enhancement
+resource/aws_route_table: Allow an existing local route to be adopted or imported and the target to be updated
+```

internal/service/ec2/vpc_route_data_source_test.go

@@ -280,7 +280,7 @@ resource "aws_instance" "test" {
 resource "aws_route" "instance" {
   route_table_id         = aws_route_table.test.id
   destination_cidr_block = "10.0.1.0/24"
-  instance_id            = aws_instance.test.id
+  network_interface_id   = aws_instance.test.primary_network_interface_id
 }
 
 data "aws_route" "by_peering_connection_id" {

internal/service/ec2/vpc_route_table.go

@@ -243,7 +243,7 @@ func resourceRouteTableRead(ctx context.Context, d *schema.ResourceData, meta in
 	if err := d.Set("propagating_vgws", propagatingVGWs); err != nil {
 		return sdkdiag.AppendErrorf(diags, "setting propagating_vgws: %s", err)
 	}
-	if err := d.Set("route", flattenRoutes(ctx, conn, routeTable.Routes)); err != nil {
+	if err := d.Set("route", flattenRoutes(ctx, conn, d, routeTable.Routes)); err != nil {
 		return sdkdiag.AppendErrorf(diags, "setting route: %s", err)
 	}
 	d.Set("vpc_id", routeTable.VpcId)
@@ -480,6 +480,25 @@ func routeTableAddRoute(ctx context.Context, conn *ec2.EC2, routeTableID string,
 
 	input.RouteTableId = aws.String(routeTableID)
 
+	_, target := routeTableRouteTargetAttribute(tfMap)
+
+	if target == gatewayIDLocal {
+		// created by AWS so probably doesn't need a retry but just to be sure
+		// we provide a small one
+		_, err := tfresource.RetryWhenAWSErrCodeEquals(ctx, time.Second*15,
+			func() (interface{}, error) {
+				return routeFinder(ctx, conn, routeTableID, destination)
+			},
+			errCodeInvalidRouteNotFound,
+		)
+
+		if tfresource.NotFound(err) {
+			return fmt.Errorf("local route cannot be created but must exist to be adopted, %s %s does not exist", target, destination)
+		}
+
+		return nil
+	}
+
 	_, err := tfresource.RetryWhenAWSErrCodeEquals(ctx, timeout,
 		func() (interface{}, error) {
 			return conn.CreateRouteWithContext(ctx, input)
@@ -719,7 +738,11 @@ func expandReplaceRouteInput(tfMap map[string]interface{}) *ec2.ReplaceRouteInpu
 	}
 
 	if v, ok := tfMap["gateway_id"].(string); ok && v != "" {
-		apiObject.GatewayId = aws.String(v)
+		if v == gatewayIDLocal {
+			apiObject.LocalTarget = aws.Bool(true)
+		} else {
+			apiObject.GatewayId = aws.String(v)
+		}
 	}
 
 	if v, ok := tfMap["local_gateway_id"].(string); ok && v != "" {
@@ -811,7 +834,7 @@ func flattenRoute(apiObject *ec2.Route) map[string]interface{} {
 	return tfMap
 }
 
-func flattenRoutes(ctx context.Context, conn *ec2.EC2, apiObjects []*ec2.Route) []interface{} {
+func flattenRoutes(ctx context.Context, conn *ec2.EC2, d *schema.ResourceData, apiObjects []*ec2.Route) []interface{} {
 	if len(apiObjects) == 0 {
 		return nil
 	}
@@ -823,7 +846,13 @@ func flattenRoutes(ctx context.Context, conn *ec2.EC2, apiObjects []*ec2.Route)
 			continue
 		}
 
-		if gatewayID := aws.StringValue(apiObject.GatewayId); gatewayID == gatewayIDLocal || gatewayID == gatewayIDVPCLattice {
+		if gatewayID := aws.StringValue(apiObject.GatewayId); gatewayID == gatewayIDVPCLattice {
+			continue
+		}
+
+		// local routes from config need to be included but not default local routes, as determined by hasLocalConfig
+		// see local route tests
+		if gatewayID := aws.StringValue(apiObject.GatewayId); gatewayID == gatewayIDLocal && !hasLocalConfig(d, apiObject) {
 			continue
 		}
 
@@ -854,6 +883,35 @@ func flattenRoutes(ctx context.Context, conn *ec2.EC2, apiObjects []*ec2.Route)
 	return tfList
 }
 
+// hasLocalConfig along with flattenRoutes prevents default local routes from
+// being stored in state but allows configured local routes to be stored in
+// state. hasLocalConfig checks the ResourceData and flattenRoutes skips or
+// includes the route. Normally, you can't count on ResourceData to represent
+// config. However, in this case, a local gateway route in ResourceData must
+// come from config because of the gatekeeping done by hasLocalConfig and
+// flattenRoutes.
+func hasLocalConfig(d *schema.ResourceData, apiObject *ec2.Route) bool {
+	if apiObject.GatewayId == nil {
+		return false
+	}
+	if v, ok := d.GetOk("route"); ok && v.(*schema.Set).Len() > 0 {
+		for _, v := range v.(*schema.Set).List() {
+			v := v.(map[string]interface{})
+			if v["cidr_block"].(string) != aws.StringValue(apiObject.DestinationCidrBlock) &&
+				v["destination_prefix_list_id"] != aws.StringValue(apiObject.DestinationPrefixListId) &&
+				v["ipv6_cidr_block"] != aws.StringValue(apiObject.DestinationIpv6CidrBlock) {
+				continue
+			}
+
+			if v["gateway_id"].(string) == gatewayIDLocal {
+				return true
+			}
+		}
+	}
+
+	return false
+}
+
 // routeTableRouteDestinationAttribute returns the attribute key and value of the route table route's destination.
 func routeTableRouteDestinationAttribute(m map[string]interface{}) (string, string) {
 	for _, key := range routeTableValidDestinations {