null_resource and templatefile using with deposed elements raise cycle error

[okgolove]

Terraform Version

Terraform v0.12.20

Terraform Configuration Files

resource "digitalocean_droplet" "test" {
  count  = 5
  image  = 57114112
  name   = "test-${format("%03d", count.index + 1)}"
  region = "ams3"
  private_networking = true
  monitoring = true
  size       = "s-2vcpu-2gb"
  tags       = ["test"]

  lifecycle {
    create_before_destroy = true
  }

  connection {
    host        = self.ipv4_address
    type        = "ssh"
    user        = "developer"
    private_key = file(pathexpand(var.private_key_path))
    certificate = file(pathexpand(var.certificate_key_path))
  }
}

resource "digitalocean_droplet" "haproxy_test" {
  count  = 1
  image  = 57065468
  name   = "haproxy-test-${format("%03d", count.index + 1)}"
  region = "ams3"
  private_networking = true
  monitoring         = true
  size = "s-2vcpu-2gb"
  tags = ["haproxy-test"]

  lifecycle {
    create_before_destroy = true
  }

  connection {
    host        = self.ipv4_address
    type        = "ssh"
    user        = "developer"
    private_key = file(pathexpand(var.private_key_path))
    certificate = file(pathexpand(var.certificate_key_path))
  }
}

resource "null_resource" "haproxy_test_config" {
  count = 1

  triggers = {
    droplets = templatefile("${path.module}/templates/haproxy/test.tpl", {droplets = digitalocean_droplet.test})
    haproxy  = digitalocean_droplet.haproxy_test[count.index].id
  }

  lifecycle {
    create_before_destroy = true
  }

  connection {
    host        = digitalocean_droplet.haproxy_test[count.index].ipv4_address
    user        = "developer"
    private_key = file(pathexpand(var.private_key_path))
    certificate = file(pathexpand(var.certificate_key_path))
  }

  provisioner "file" {
    content     = templatefile("${path.module}/templates/haproxy/test.tpl", {droplets = digitalocean_droplet.test})
    destination = "/tmp/haproxy"
  }

  provisioner "remote-exec" {
    inline = [
      "sudo cp /tmp/haproxy /etc/haproxy/haproxy.cfg",
      "sudo systemctl reload haproxy",
    ]
  }
}

test.tpl:

backend torg
    mode http
    http-check expect status 200
    option httpchk GET /health-check
    balance roundrobin
    %{ for test in droplets ~}
server ${test.name} ${test.ipv4_address_private}:8080 check fall 3 rise 2
    %{ endfor }

Debug Output

https://gist.github.com/okgolove/2a126205e8bf92871c5dbc1cbdccd069

Crash Output

Expected Behavior

test droplet has been destroyed, null_resource has been reprovisioned

Actual Behavior

Error: Cycle: null_resource.haproxy_test_config[0], null_resource.haproxy_test_config[0] (destroy deposed bca85ac3), digitalocean_droplet.test[2] (destroy)

Steps to Reproduce

1. terraform init
2. terraform apply
3. Reduce test's count to 4
4. terraform apply

Additional Context

References

[ghost]

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