Terraform 0.11 - Add NAT Gateway to Database route table

[KyleMartin901]

This commit corrects the configuration of the create_database_nat_gateway_route feature where it adds a route to allow the databse subnets access to the internet.

Previously this feature would add the NAT gateway to the private subnet route table and not the database route table causing a conlict in configuration as both aws_route.private_nat_gateway and aws_route.database_nat_gateway would both want to add a route for destination_cidr_block = "0.0.0.0/0" which will cause the following error

Error: Error applying plan:

3 errors occurred:
        * module.vpc.aws_route.database_nat_gateway[0]: 1 error occurred:
        * aws_route.database_nat_gateway.0: Error creating route: RouteAlreadyExists: The route identified by 0.0.0.0/0 already exists.
        status code: 400, request id: f64ae1fb-e56d-4eed-9117-97d392f0e8c4

        * module.vpc.aws_route.database_nat_gateway[1]: 1 error occurred:
        * aws_route.database_nat_gateway.1: Error creating route: RouteAlreadyExists: The route identified by 0.0.0.0/0 already exists.
        status code: 400, request id: f5ac8726-ea1c-46b1-9a76-794efc95542b

        * module.vpc.aws_route.database_nat_gateway[2]: 1 error occurred:
        * aws_route.database_nat_gateway.2: Error creating route: RouteAlreadyExists: The route identified by 0.0.0.0/0 already exists.
        status code: 400, request id: 9edbe494-2407-4552-88bd-498379da7dc8

Because there is only a single route table for the Database subnets even if they are multi AZ enabled I have selected to follow the standard that is in the aws_route.database_internet_gateway resource where the association is done for the first route table and NAT gateway.

[pnduati]

@antonbabenko Hey! Can this be merged, I did a VPC design, where we are launching ec2 resources in the DB subnet and we have to add the nat to the route table, it would be awesome if all this is handled by the VPC module instead of having to build a custom resource in the module to update the route table.

[bryantbiggs]

hi all, this is fixed in #518 for the current versions supported. unfortunately, we are not supporting Terraform 0.11.x anymore

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