Setting instance_count = 0 leads to error with Terrafrom 0.12

[dermyrddin]

In my setup I have modules with instance_count = 0 for some environments.
Upgrading to Terraform 0.12 breaks this setup:

Error: Error in function call

  on .terraform/modules/file_rating_mongo_4/terraform-aws-modules-terraform-aws-ec2-instance-6557b76/outputs.tf line 10, in locals:
  10:   this_placement_group              = compact(concat(coalescelist(aws_instance.this.*.placement_group, aws_instance.this_t2.*.placement_group), [""]))
    |----------------
    | aws_instance.this is empty tuple
    | aws_instance.this_t2 is empty tuple

Call to function "coalescelist" failed: no non-null arguments.

This happens because behaviour of coalescelist function used in outputs.tf has been changed in Terraform 0.12: hashicorp/terraform#21370

[hieuhtr]

Hmm, this issue is unpredictable, as far as I know.
I'm facing the same issue when setting instance_count = "1" or instance_count = 1

I don't have any workaround here, but after some terraform plan, this issue is bypassed
You may try to not define instance_count in your module section.

[butson]

I don't understand why the setting of thisi_placement_group is different than the other variables.

Shouldn't

this_placement_group = compact(concat(coalescelist(aws_instance.this..placement_group, aws_instance.this_t2..placement_group), [""]))

be

this_placement_group = compact(coalescelist(aws_instance.this..placement_group, aws_instance.this_t2..placement_group, [""]))

or something similiar, that is add an a list of one empty string if others are null

[antonbabenko]

Thanks for opening this issue. This has been just fixed and v2.5.0 has been released.

[github-actions]

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