Output resource not committed to tfstate file

[packplusplus]

If an output references a resource attribute that doesn't exist, the output fails silently and doesn't show up in the tfstate file.

In my case, a subnet didn't have auto assign ip turned on, and when an instance was launched there, no output showed up. Here's a simplified test case. You need to disable auto-assign ip in the default subnets for this test case to work. I assume it applies to all calculated attributes / values.

FWIW: referencing variables that don't exist errors on compile. Maybe calculated variables / attributes should dereference as "false" or "" if the data doesn't exist.

provider "aws" {
  region = "us-west-2"
}

resource "aws_instance" "test" {
  #centos6 community
  ami = "ami-81d092b1"
  instance_type = "t2.micro"

  associate_public_ip_address = false
}

output "test" {
  value = "echo ${aws_instance.test.public_ip}"
}

output

$ terraform apply
aws_instance.test: Creating...
  ami:                         "" => "ami-81d092b1"
  associate_public_ip_address: "" => "0"
  availability_zone:           "" => "<computed>"
  ebs_block_device.#:          "" => "<computed>"
  ephemeral_block_device.#:    "" => "<computed>"
  instance_type:               "" => "t2.micro"
  key_name:                    "" => "<computed>"
  placement_group:             "" => "<computed>"
  private_dns:                 "" => "<computed>"
  private_ip:                  "" => "<computed>"
  public_dns:                  "" => "<computed>"
  public_ip:                   "" => "<computed>"
  root_block_device.#:         "" => "<computed>"
  security_groups.#:           "" => "<computed>"
  source_dest_check:           "" => "1"
  subnet_id:                   "" => "<computed>"
  tenancy:                     "" => "<computed>"
  vpc_security_group_ids.#:    "" => "<computed>"
aws_instance.test: Creation complete

Apply complete! Resources: 1 added, 0 changed, 0 destroyed.

The state of your infrastructure has been saved to the path
below. This state is required to modify and destroy your
infrastructure, so keep it safe. To inspect the complete state
use the `terraform show` command.

State path: terraform.tfstate
$ terraform show
aws_instance.test:
  id = i-6ff3b6b6
  ami = ami-81d092b1
  associate_public_ip_address = false
  availability_zone = us-west-2b
  ebs_block_device.# = 0
  ebs_optimized = false
  ephemeral_block_device.# = 0
  iam_instance_profile = 
  instance_type = t2.micro
  monitoring = false
  private_dns = ip-172-31-25-150.us-west-2.compute.internal
  private_ip = 172.31.25.150
  public_dns = 
  root_block_device.# = 1
  root_block_device.0.delete_on_termination = false
  root_block_device.0.iops = 24
  root_block_device.0.volume_size = 8
  root_block_device.0.volume_type = gp2
  security_groups.# = 0
  source_dest_check = true
  subnet_id = subnet-b3aa40c4
  tags.# = 0
  tenancy = default
  vpc_security_group_ids.# = 1
  vpc_security_group_ids.434905629 = sg-2462e741

$ terraform output
The state file has no outputs defined. Define an output
in your configuration with the `output` directive and re-run
`terraform apply` for it to become available.

[stack72]

@packplusplus you don't need the echo

output "test" {
  value = "${aws_instance.test.public_ip}"
}

[mitchellh]

Going to centralize on other dups of this, see #5334

[ghost]

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