output dependency not being read by input

[fraz78]

Hi folks,

I have a security group module that has the below output

output "id" {
  value = aws_security_group.main.id
}

when i run terragrunt output against the security group module it returns the following output value

arn = "arn:aws:ec2:eu-west-2:83160456789:security-group/sg-095f26bc2025abcde"
id = "sg-095f26bc2025abcde"

however, when i try to call the above output in my rds module using a dependency in my terragrunt.hcl file, i get the following

│ Error: Variables not allowed
│ 
│   on <value for var.vpc_security_group_ids> line 1:
│   (source code not available)
│ 
│ Variables may not be used here.

the variable in my rds module is setup as follows

variable "vpc_security_group_ids" {
  description = "List of VPC security groups to associate"
  type        = list(string)
  default     = []
}

my terragrunt.hcl file is setup as follows. Please note that i have been able to pass the hard coded security group value (commented out below) and get it to deploy successfully, but as soon as i attempt to use the dependency.sg.outputs.id it fails with the above error. For the record, i have tried wrapping it as ["dependency.sg.outputs.id"] but this is then read in as a string and not a dynamic value.

dependency "sg" {
  config_path = "../sg/rds"
}

dependency "subnet" {
  config_path = "../subnet/mft-subnet"
}

inputs = {

  # vpc_security_group_ids  = ["sg-095f26bc2025abcde"] 
  vpc_security_group_ids     = dependency.sg.outputs.id
  subnet_ids                 = dependency.subnet.outputs.aws_subnets.main.ids

Any idea of what may be causing this???????

For the record, the subnet_ids in the above example in contrast works fine. It's output and variable are defined below for reference purposes only:

aws_subnets = {
  "main" = {
    "ids" = [
      "subnet-02132b73acfeabcderr",
      "subnet-050d63659cd5abcdedf",
    ]
  }
}
module = {}


variable "subnet_ids" {
  description = "A list of VPC subnet IDs"
  type        = list(string)
  default     = []
}

---

Tracked in ticket #110257

[james00012]

Hey @fraz78, is it possible that the variable is expecting a list and you are passing in a string?
Based on your output, it seems like dependency.sg.outputs.id would be a string, rather than a list.

[fraz78]

I did think of that, and tried changing the variable type from list(string) to string but it didn't seem to make a difference.

[denis256]

Hi, the variable can be wrapped in [] to convert it to a list...

inputs = {
  vpc_security_group_ids     = [ dependency.dep.outputs.id ]
}

Simplified example in:
https://github.com/denis256/terragrunt-tests/tree/master/discussion-738

[fraz78]

@denis256
Thanks this resolved the issue.

[fraz78]

@denis256 I have noticed that if i move the input vpc_security_group_ids = [ dependency.dep.outputs.id ] into another file called config.hcl and then merge the input into the terragrunt.hcl file it fails to read the dependency. Does the dependency block also need to be added to the config.hcl file?

[denis256]

Hi,
depends on how is intended to be used included file, usually approach with merge_strategy = "deep" works fine:

include "inputs" {
  path   = "inputs.hcl"
  merge_strategy = "deep"
}