Cannot use complex input variable types (lists)

[karelorigin]

# image.pkr.hcl
variable "foo" {
  type = list(string)
}

# main.tf
resource "packer_image" "image" {
  file             = data.packer_files.image.file
  force            = false
  keep_environment = true

  variables = {
    foo = ["bar"]
  }
}

results in

Inappropriate value for attribute "variables": element "foo": string required.

[simaotwx]

Unfortunately there is currently no support for complex data types – only strings. You could convert it to a JSON in Terraform using jsonencode and decode it in Packer using jsondecode.

I might implement this in the future, though.

[karelorigin]

Ah, I see. I figured it was due to some kind of type conversion limitation. The jsonencode/decode solution should do the trick for now :)

[simaotwx]

Just for the record: Currently variables are passed to Packer using the -var command line parameter. I'm considering changing this and implement it the following way:

1. A temporary JSON file is created in a temporary location (e. g. /tmp or %USERPROFILE%/AppData/Local/Tmp) with all variables
2. Packer is passed the -var-file parameter to use that JSON file
3. When done, the temporary file is deleted

This has multiple advantages:

• No command line length limit
• Arbitrary, even binary values could be passed from a purely technical perspective without mangling any of the data
• Any type can be passed through (not just strings)

[karelorigin]

Hi @simaotwx,

Thanks for the update. I always thought this provider simply imported Packer as a library rather than calling it externally. Is that not possible? And if so, wouldn't that make temporary files unnecessary?

[simaotwx]

Hi @karelorigin it does import Packer, however currently it only invokes the Main function, passing the command line parameters as an array to said Main function. To isolate the address space (heap and stack) as well as the environment, the provider is invoked as a program in "Packer mode", effectively acting as if it was the Packer binary itself. That was the easiest and most straightforward way to embed Packer without many modifications, however, I'd be happy to explore better options.

[karelorigin]

Personally, I'm relying on Terraform Cloud to manage TF state and it doesn't seem very fond of files on disk (even in the tmp directory). I've even created my own provider to work around it, so I think anything relying on too many local sources is likely to break.

[simaotwx]

That's a good point. We use Terraform Cloud, too, and I don't know how /tmp behaves there. Complex data types can also be passed on the command line but I fear that it would cause issues related to the command line length and encoding.

[nwmcsween]

Could this not be implemented using the https://github.com/hashicorp/terraform-plugin-sdk/issues/248 DynamicPseudoType and then just quote the var passed to packer e.g. -var 'list=["foo". "bar"]'

[simaotwx]

Will attempt to implement this using DynamicPseudoType in the next round of updates.

[simaotwx]

I have implemented partial support for this in the 0.16.0 release. Please let me know if it's enough to support your use case.

[simaotwx]

Version 0.16.0 supports string lists as this issue asks for. I'm going to close this issue for that reason.