Allow module to depend on another module

[Raviadonis]

Current Terraform Version

Terraform v0.11.6

Use-cases

I have two different files. (ie., module.tf and resource.tf)

Have written two modules in a single module.tf. The second module should run once after the first module ran successfully. Each module has to run a provisioner within the null_resource with a different set of variables appropriate to the modules. So thought of making one module is dependent on another module.

Attempted Solutions

RESOURCE.TF:

resource "aws_instance" "testapp" {
  count                                = "${var.count}"
  ami                                   = "${var.ami_id}"
  key_name                         = "${var.key_name}"
  subnet_id                          = "${var.aws_subnet}"
  private_ip                          = "${var.private_ip}"
  instance_type                   = "${var.instance_type}"
  security_groups                = ["${var.security_groups}"]
  availability_zone               = "${var.availability_zone}"

  root_block_device {
  volume_type                      = "gp2"
  volume_size                       = "${var.root_volume}"
  delete_on_termination      = "true"
  }

  tags {
  Name                                 = "${var.name}${format("%02d", count.index + var.name_suffix)}"
  Owner                                = "${var.owner}"
  Project                                = "${var.project}"
     }
  }


resource "null_resource" "cluster" {

 provisioner "file" {
  source                                 = "${template_dir.scripts.destination_dir}"
  destination                          = "/home/user1/"
   }

 connection {
   host                                = "${element(aws_instance.testapp.*.private_ip, count.index)}"
   type                                = "ssh"
   user                                = "user1"
   private_key                     = "${file("/tmp/cluster/test_key_pair.pem")}"
   }

  provisioner "remote-exec" {
   inline                              = ["sh -x /home/user1/${var.destination}"]
   }
}

output "instance_id" {
  value = "${aws_instance.testapp.id}"
}

MODULE.TF:

module "node_1" {
  source                               = "../../resources/compute"
  ami_id                               = "${var.ami_id}"
  key_name                          = "${var.key_name}"
  private_ip                          = "${var.private_ip}"
  aws_subnet                       = "${var.aws_subnet}"
  name_suffix                          = "${var.name_suffix_dc}"
  destination                          = "${var.destination}"
  root_volume                          = "${var.root_volume}"
  instance_type                        = "${var.instance_type}"
  security_groups                      = ["${var.security_groups}"]
  availability_zone                    = "${var.availability_zone}"

  ### Tag variables ###
  os                                       = "${var.os}"
  name                                 = "${var.hostname}"
  owner                                = "${var.owner}"
  project                              = "${var.project}"
  additional_volume_size    = "${var.additional_volume_size}"
  }


module "node_2" {
  depends_on                           = ["${module.node_1.instance_id}"]
  source                               = "../../resources/compute"
  ami_id                               = "${var.ami_id}"
  key_name                             = "${var.key_name}"
  private_ip                           = "${var.private_ip}"
  aws_subnet                           = "${var.aws_subnet}"
  destination                          = "${var.destination}"
  name_suffix                          = "${var.name_suffix_hc}"
  root_volume                          = "${var.root_volume}"
  instance_type                        = "${var.instance_type}"
  security_groups                      = ["${var.security_groups}"]
  availability_zone                    = "${var.availability_zone}"
  
    ### Tag variables ###
  os                                           = "${var.os}"
  name                                      = "${var.hostname}"
  owner                                     = "${var.owner}"
  project                                    = "${var.project}"
  additional_volume_size          = "${var.additional_volume_size}"
  }

**Note:**Both module using the same resource.tf file

Output

module root: module node_2: depends_on is not a valid argument

References

#10462

[Prabhakar-cg]

This is something really necessary while launching multiple applications with same resources. Does anyone have any inputs or suggestions for this issue?.

[Raviadonis]

Prior to 0.8.0, we have to trick Terraform to do it with a combination of outputs and other trickery. But Terraform still doesn't allow a module to depend on another module directly via depends_on -- this attribute is not available for modules whatsoever.

[jbardin]

Hi @Raviadonis,

Thanks for filing this. We're tracking this feature in the referenced issue #10462. Modules can already be the target of depends_on, so the remaining issue is that depends_on cannot be used in a module itself. That issue is still outstanding because it's dependent on major changes in how terraform operates, for example data sources are going to require something along the lines of #17034 first. Once that can be implemented, there would be nothing else needed for this to work.

Thanks!

[ghost]

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