title: Terraform "Error: Unknown root level key"
body: <p>I've been searching for awhile and found posts on the Terraform errors "Unknown root level key" but nothing seems to quite match my scenario. So my first question is what does this error message mean? It sounded to me like maybe a variable was undefined in the root module but that does not appear to be the case.</p>
  
  <p>command and results:</p>
  
  <pre><code>terraform init
  "Error: Unknown root level key"
  </code></pre>
  
  <p>code:</p>
  
  <pre><code>#variables.tf file in the root module
  variable "rds_sg"{}
  #adding the line below leads to the error above
  rds_sg                      = "${module.network.hcs-rds-sg-id}" 
  </code></pre>
  
  <p>I confirmed that this output does exist in the network module. I think maybe I am missing something on how to properly refer to a module output from the root module but after a few hours of investigation I am not sure what it is.</p>