Error: Invalid value for module argument

[jeremywadsack]

When trying to migrate our configuration to 3.0.0, I ran into a syntax/type error. I tested this using the example from the documentation and it produces the same error:

Error: Invalid value for module argument

  on gclb/main.tf line 35, in module "gce-lb-https":
  35:   backends = {
  36:     default = {
  37:       description                     = null
  38:       protocol                        = "HTTP"
  39:       port                            = 443
  40:       port_name                       = "default-https"
  41:       timeout_sec                     = 10
  42:       connection_draining_timeout_sec = null
  43:       enable_cdn                      = false
  45:       health_check = {
  46:         check_interval_sec  = null
  47:         timeout_sec         = null
  48:         healthy_threshold   = null
  49:         unhealthy_threshold = null
  50:         request_path        = "/"
  51:         port                = 443
  52:         host                = null
  53:       }
  55:       groups = [
  56:         {
  57:           # Each node pool instance group should be added to the backend.
  58:           group                        = var.backend
  59:           balancing_mode               = null
  60:           capacity_scaler              = null
  61:           description                  = null
  62:           max_connections              = null
  63:           max_connections_per_instance = null
  64:           max_connections_per_endpoint = null
  65:           max_rate                     = null
  66:           max_rate_per_instance        = null
  67:           max_rate_per_endpoint        = null
  68:           max_utilization              = null
  69:         },
  70:       ]
  71:     }
  72:   }

The given value is not suitable for child module variable "backends" defined
at
.terraform/modules/lb.gce-lb-https/terraform-google-modules-terraform-google-lb-http-d65708d/variables.tf:62,1-20:
element "default": attribute "protocol": string required.

The error message at the end ("element "default": attribute "protocol": string required.") changes from one attribute to another when I re-run terraform apply:

element "default": attribute "protocol": string required.
element "default": attribute "enable_cdn": bool required.
element "default": attribute "timeout_sec": number required.
element "default": attribute "port": number required.

No matter what the message is, the type always is correct. e.g. in the error above, you see protocol is "HTTP", which is a string.

I've got the latest terraform:

$ terraform --version
Terraform v0.12.18

And I've pinned GoogleCloudPlatform/lb-http/google at version 3.0.0 (clearly because when I try 2.0.0 I get "argument "backend_params" is required" error which makes sense because that syntax changed).

Any ideas where to look on this one? I'm kinda stumped.

[jeremywadsack]

I have resolved this.

The errors were not pointing to the correct invalid value. The problem I had was that var.backend was a list(string) rather than a string. My solution was to map this:

       groups = [
         # Each node pool instance group should be added to the backend.
         for backend in var.backend:
         {
           group                        = backend
           balancing_mode               = null
           ...
         }
       ]