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layout	page_title	sidebar_current	description
docs	Creating Modules	docs-modules-create	How to create modules.

Creating Modules

Creating modules in Terraform is easy. You may want to do this to better organize your code, to make a reusable component, or just to learn more about Terraform. For any reason, if you already know the basics of Terraform, then creating a module is a piece of cake.

Modules in Terraform are folders with Terraform files. In fact, when you run terraform apply, the current working directory holding the Terraform files you're applying comprise what is called the root module. This itself is a valid module.

Therefore, you can enter the source of any module, satisfy any required variables, run terraform apply, and expect it to work.

An Example Module

Within a folder containing Terraform configurations, create a subfolder called child. In this subfolder, make one empty main.tf file. Then, back in the root folder containing the child folder, add this to one of your Terraform configuration files:

module "child" {
  source = "./child"
}

You've now created your first module! You can now add resources to the child module.

Note: Prior to running the above, you'll have to run the get command for Terraform to sync your modules. This should be instant since the module is a local path.

Inputs/Outputs

To make modules more useful than simple isolated containers of Terraform configurations, modules can be configured and also have outputs that can be consumed by your Terraform configuration.

Inputs of a module are variables and outputs are outputs. There is no special syntax to define these, they're defined just like any other variables or outputs. You can think about these variables and outputs as the API interface to your module.

Let's add a variable and an output to our child module.

variable "memory" {}

output "received" {
  value = "${var.memory}"
}

This will create a required variable, memory, and then an output, received, that will be the value of the memory variable.

You can then configure the module and use the output like so:

module "child" {
  source = "./child"

  memory = "1G"
}

output "child_memory" {
  value = "${module.child.received}"
}

If you now run terraform apply, you see how this works.

Paths and Embedded Files

It is sometimes useful to embed files within the module that aren't Terraform configuration files, such as a script to provision a resource or a file to upload.

In these cases, you can't use a relative path, since paths in Terraform are generally relative to the working directory from which Terraform was executed. Instead, you want to use a module-relative path. To do this, you should use the path interpolated variables.

resource "aws_instance" "server" {
  # ...

  provisioner "remote-exec" {
    script = "${path.module}/script.sh"
  }
}

Here we use ${path.module} to get a module-relative path.

Nested Modules

You can nest a module within another module. This module will be hidden from your root configuration, so you'll have to re-expose any variables and outputs you require.

The get command will automatically get all nested modules.

You don't have to worry about conflicting versions of modules, since Terraform builds isolated subtrees of all dependencies. For example, one module might use version 1.0 of module foo and another module might use version 2.0, and this will all work fine within Terraform since the modules are created separately.

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