Output local_filename is available _before_ the package is available

[lorengordon]

Description

I was attempting to build the package locally once, and then use it several times in different lambda functions. That ends up looking something like this:

module "test_create_package" {
  source = "git::https://github.com/terraform-aws-modules/terraform-aws-lambda.git?ref=v4.0.2"

  create_function = false
  create_package  = true

  recreate_missing_package = false

  runtime     = "python3.8"
  source_path = "${path.module}/../../lambda/src"
}

module "test_create_function" {
  source = "git::https://github.com/terraform-aws-modules/terraform-aws-lambda.git?ref=v4.0.2"

  function_name = "foo"
  handler       = "index.lambda_handler"
  runtime       = "python3.8"

  create_package = false
  local_existing_package = module.test_create_package.local_filename
}

The problem is that the output local_filename is determined immediately at plan time, but the zip is only created in the apply phase. Which means the terraform graph determines that it is able to use the value immediately in the apply phase to create the lambda function. Which results in errors of the form:

│ Error: unable to load "./builds/4d797a72c1bf2fcf10fcee1ece41ecf3e1ec6c99ea87c4772711bc449c5bad4b.zip": open ./builds/4d797a72c1bf2fcf10fcee1ece41ecf3e1ec6c99ea87c4772711bc449c5bad4b.zip: no such file or directory
│
│   with module.test_create_function.module.lambda.aws_lambda_function.this[0],
│   on .terraform/modules/test_create_function.lambda/main.tf line 22, in resource "aws_lambda_function" "this":
│   22: resource "aws_lambda_function" "this" {

I believe this can be fixed by adding a depends_on statement to the output local_filename for null_resource.archive:

output "local_filename" {
  description = "The filename of zip archive deployed (if deployment was from local)"
  value       = local.filename

  depends_on = [
    null_resource.archive,
  ]
}

I'll be testing that and opening a pull request shortly if it does indeed fix the behavoir.

• [x] ✋ I have searched the open/closed issues and my issue is not listed.

[antonbabenko]

Not sure if depends_on between modules will help with this. Worth trying.

route53 module has such a solution already.

[lorengordon]

Yes, that is also an option, but module-level depends_on does some ugly things to the graph. Forcing the output to wait keeps the graph really clean.

[lorengordon]

And I did just test my fork with this change and it does indeed fix the problem...

[antonbabenko]

This issue has been resolved in version 4.1.1 :tada:

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