How do I deploy an API gateway proxy properly with configuration_aliases?

[zackproser]

A customer asked:

We're trying to deploy an API gateway proxy with Gruntwork's module. The code we've created looks like this:

terraform {
  source = "git::[email protected]:gruntwork-io/terraform-aws-lambda.git//modules/api-gateway-proxy?ref=v0.21.8"
  }
   
  # Include the `terragrunt.hcl` located in the root of our Reference Architecture's
  # repository because this file contains all the templating required to make our
  # Terraform state and AWS provider DRY.
  include {
  path = find_in_parent_folders()
  }
   
  inputs = {
    api_name = "test-api"
    lambda_functions = {
    "" = "ingest-test"
  }
}

---

Tracked in ticket #110135

[zackproser]

Gruntwork's API Proxy module has a configuration_aliases config that requires a provider explicitly aliased to us_east_1 to be passed in.

Here's an example in pure Terraform of how you would pass in such an alias:

# ---------------------------------------------------------------------------------------------------------------------
# USE API GATEWAY TO EXPOSE LAMBDA FUNCTION
# ---------------------------------------------------------------------------------------------------------------------

module "api_gateway" {
  # When using these modules in your own templates, you will need to use a Git URL with a ref attribute that pins you
  # to a specific version of the modules, such as the following example:
  # source = "git::[email protected]:gruntwork-io/terraform-aws-lambda.git//modules/api-gateway-proxy?ref=v1.0.8"
  source = "../../../modules/api-gateway-proxy"
  providers = {
    aws = aws

    # NOTE: this is only necessary if you are configuring an EDGE domain (globally optimized API Gateway endpoint using
    # CloudFront). For other cases, this can be configured to the base `aws` provider.
    aws.us_east_1 = aws.us_east_1
  }

  api_name = var.name
  lambda_functions = {
    # Empty string key means proxy everything
    "" = module.lambda.function_name
  }
... truncated for brevity ...

However, when working with Terragrunt code, we use generate blocks to create the provider blocks we need. By default, with the Reference Architecture, we only generate a single such provider block and it has no alias.

Conversely, for multi-region modules, we generate a bunch of provider blocks, each with an alias.

To make this one API proxy module work, for example, you'd need to generate a single provider block:

generate "providers" {
  path      = "providers-custom.tf"
  if_exists = "overwrite"
  contents  = <<EOF
provider "aws" {
  region = "us-east-1"
  alias = "us_east_1"
}
EOF
}