How do I see object values when debugging terraform

Question

When writing a terraform module I often run in errors like this:

Error: Invalid index

  on ../../../modules/host/main.tf line 7, in resource "aws_network_interface" "host":
   7:   subnet_id = data.aws_subnet_ids.current[each.key].ids[0]
    |----------------
    | data.aws_subnet_ids.current is object with 2 attributes
    | each.key is "lab"

There are all kinds of reasons why this happens. Usually it is because what I think a certain object will contain is incorrect.

In order to help debugging this it would be usefull to at least see what the object contains. "Object with 2 attributes" is rather vague. I would like to know what attribtues it has, so I can add the necessary transformations to end up with the string I need here.

So is there a way? Can you in some way run "terraform plan" in such that the contents of those objects are actually displayed when the plan runs in to an error?

Answer 1

You can run "terraform console" command and put directly your expressions. eg. Suppose for given map in variable file you want to see flattened list.

variable "podmap" {
   type  = "map"
   default = {
       dev = ["pod1", "pod6"]
       qa =  ["pod5"]
       uat = ["pod5"]
       testenv = []
  }
}

Run terraform console:

$ terraform console
> flatten([for podtype, podlist in var.podmap : [for podname in podlist : { name = podname, type = podtype }]])flatten([for podtype, podlist in var.podmap : [for podname in podlist : { name = podname, type = podtype }]])

Based on your expression/statement it will give you output accordingly.

for above flatten function you will get below output list which you cannot see while you do terraform plan.

[
  {
    "name" = "pod5"
    "type" = "dev"
  },
  {
    "name" = "pod6"
    "type" = "dev"
  },
  {
    "name" = "pod5"
    "type" = "qa"
  },
  {
    "name" = "pod5"
    "type" = "uat"
  },
]

Answer 2

**** Warning: this could potentially write sensitive data to disk, use with caution ****

To see the contents of an object create a temporary local_file resource and set it's content property to the object converted to json. It will then be displayed in the plan. Once you are done remove the resource. For example:

resource "local_file" "this" {
    content  = jsonencode(your object)
    filename = "a valid file path"
}