Deprecate `name_prefix`

[danawillow]

Right now, a few of our resources support specifying the name in multiple ways:

• A name field, which is for the name explicitly
• A name_prefix field, which specifies a prefix and generates a random string for the rest
• Setting neither, which generates a random string

Because of the existence of the random provider, we don't need to have this logic inside the google resources, and getting rid of it will make the entire provider more consistent (since only some resources support name_prefix anyway).

We can do this safely in two steps:

• Add import capability to the random_id resource to allow setting its output to a user-specified value. This would allow users to transition to the random_id resource without needing to recreate their google resources, allowing them to do that transition on their own time instead of waiting for an opportunity when the resource would need to be recreated to make the change.
• Deprecate the name_prefix field and make it computed so users can remove it from their configs without recreating the resource

@rosbo @paddycarver to make sure this checks out based on our conversation

[rosbo]

👍

[danawillow]

@sl1pm4t here's what I'm thinking about for your scenario:

variable "machine_type" {}

resource "google_container_cluster" "is-1035" {
  name               = "is-1035"
  zone               = "us-central1-a"
  initial_node_count = 1
}

resource "random_id" "np" {
  byte_length = 2
  keepers = {
    machine_type = "${var.machine_type}"
  }
}

resource "google_container_node_pool" "is-1035" {
  name               = "is-1035-${random_id.np.hex}"
  zone               = "us-central1-a"
  cluster            = "${google_container_cluster.is-1035.name}"
  node_count         = 1

  node_config {
    machine_type = "${var.machine_type}"
  }

  lifecycle {
    create_before_destroy = true
  }
}

The keepers parameter in random_id gives a map of values that cause the random id to be regenerated, so by tying it to attributes that you think might change, it'll make sure the random id changes too.

[sl1pm4t]

Yeah, that could be a pretty elegant solution @danawillow.
I'll try it out, thanks!

[paddycarver]

That matches my understanding.

[sl1pm4t]

@danawillow I tried out the alternative and it works well. Thanks!

[danawillow]

I tested this flow out with a build of the random provider with my changes and it works:

resource "google_compute_instance_template" "foobar" {
  # name_prefix = "is-1054-"
  name         = "${random_id.rand.dec}"
  machine_type = "n1-standard-1"

  disk {
    source_image = "debian-8-jessie-v20160803"
    auto_delete  = true
    boot         = true
  }

  network_interface {
    network = "default"
  }
}

resource "random_id" "rand" {
  byte_length = 11
  prefix      = "is-1054-"
}

where originally, name_prefix was filled in and not name.

Imported random_id.rand with the following command:

terraform import random_id.rand is-1054-,ELFZ1rbrAThoeQE

The base64 encoding came from this script: https://play.golang.org/p/9KrkDoxRTOw
The value of "val" in the script came from running terraform show and looking for the value of name:

google_compute_instance_template.foobar:
  ...
  name = is-1054-20180329213336514500000001

[danawillow]

Fixed in #1035