main.tf

data "aws_caller_identity" "current" {}
data "aws_region" "current" {}

resource "random_pet" "random" {
  length = 2
}

resource "aws_api_gateway_rest_api" "api" {
  name = random_pet.random.id
}

resource "aws_api_gateway_resource" "resource" {
  path_part   = "cors"
  parent_id   = aws_api_gateway_rest_api.api.root_resource_id
  rest_api_id = aws_api_gateway_rest_api.api.id
}

resource "aws_api_gateway_method" "method" {
  rest_api_id   = aws_api_gateway_rest_api.api.id
  resource_id   = aws_api_gateway_resource.resource.id
  http_method   = "POST"
  authorization = "NONE"
}

resource "aws_api_gateway_integration" "integration" {
  rest_api_id             = aws_api_gateway_rest_api.api.id
  resource_id             = aws_api_gateway_resource.resource.id
  http_method             = aws_api_gateway_method.method.http_method
  integration_http_method = "POST"
  type                    = "AWS_PROXY"
  uri                     = "arn:aws:apigateway:${data.aws_region.current.name}:lambda:path/2015-03-31/functions/${aws_lambda_function.lambda.arn}/invocations"
}

resource "aws_api_gateway_deployment" "deployment" {
  rest_api_id = aws_api_gateway_rest_api.api.id
  stage_name  = "dev"

  triggers = {
    # NOTE: The configuration below will satisfy ordering considerations,
    #       but not pick up all future REST API changes. More advanced patterns
    #       are possible, such as using the filesha1() function against the
    #       Terraform configuration file(s) or removing the .id references to
    #       calculate a hash against whole resources. Be aware that using whole
    #       resources will show a difference after the initial implementation.
    #       It will stabilize to only change when resources change afterwards.
    redeployment = sha1(jsonencode([
      aws_api_gateway_resource.resource.id,
      aws_api_gateway_method.method.id,
      aws_api_gateway_integration.integration.id,
    ]))
  }

  lifecycle {
    create_before_destroy = true
  }
}

resource "aws_lambda_permission" "apigw_lambda" {
  statement_id  = "AllowExecutionFromAPIGateway"
  action        = "lambda:InvokeFunction"
  function_name = aws_lambda_function.lambda.arn
  principal     = "apigateway.amazonaws.com"
  source_arn    = "${aws_api_gateway_rest_api.api.execution_arn}/*/*/*"
}

resource "aws_iam_role" "role" {
  name = random_pet.random.id

  assume_role_policy = <<POLICY
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Action": "sts:AssumeRole",
      "Principal": {
        "Service": "lambda.amazonaws.com"
      },
      "Effect": "Allow",
      "Sid": ""
    }
  ]
}
POLICY
}

resource "aws_lambda_function" "lambda" {
  filename      = "lambda.zip"
  function_name = random_pet.random.id
  role          = aws_iam_role.role.arn
  handler       = "lambda.handler"

  source_code_hash = filebase64sha256("lambda.zip")

  runtime = "nodejs16.x"

  environment {
    variables = {
      foo = "bar"
    }
  }
}

output "api_url" {
  value = aws_api_gateway_deployment.deployment.invoke_url
}