Add var.create_origin_bucket

[alexjurkiewicz]

This adjustment allows for a slight improvement in functionality -- it's now possible to have this module create the origin bucket, but manually specify the name to use.

This change works around a problem where it's not possible to use a computed value for the origin bucket value. For example, if you create an S3 bucket using the Cloudposse S3 bucket module, you'll see an error like:

Error: Invalid count argument

on .terraform/modules/my_cdn/main.tf line 312, in data "aws_s3_bucket" "origin": 312: count = local.enabled && (var.origin_bucket != null) ? 1 : 0

The "count" value depends on resource attributes that cannot be determined until apply, so Terraform cannot predict how many instances will be created. To work around this, use the -target argument to first apply only the resources that the count depends on.

Unfortunately this fix just moves the corner case, rather than eliminating it. If a user specifies an existing bucket for var.origin_bucket, they must set create_origin_bucket to false or a spurious bucket will be created.

---

what

I ran into this problem while deploying a simple CDN as follows:

module "label" {
  source    = "git::https://github.com/cloudposse/terraform-null-label.git?ref=0.24.1"
  # ...
}
module "origin_bucket" {
  source  = "cloudposse/s3-bucket/aws"
  context = module.label.context
  # ...
}
module "cdn" {
  source  = "cloudposse/cloudfront-s3-cdn/aws"
  context = module.label.context
  origin_bucket = module.origin_bucket.bucket_id
  # ...
}

why

• It's sad Terraform has no ability to completely squash this corner case. But it's good to eliminate the possibility of accidentally building non-reproducible Terraform configurations

[mergify[bot]]

This pull request is now in conflict. Could you fix it @alexjurkiewicz? 🙏

[nitrocode]

just wondering if you set origin_bucket = module.label.id and set a depends_on, would this work without this pr change?

module "cdn" {
  source        = "cloudposse/cloudfront-s3-cdn/aws"
  context       = module.label.context
  origin_bucket = module.label.id
  # ...
  depends_on = [module.origin_bucket]
}

[mergify[bot]]

This pull request is now in conflict. Could you fix it @alexjurkiewicz? 🙏

[sebastianmacarescu]

I also think this is very useful in case we want to override the origin bucket name while still allowing this module to create it.