128 lines
4.1 KiB
Markdown
128 lines
4.1 KiB
Markdown
---
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layout: "docs"
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page_title: "Creating Modules"
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sidebar_current: "docs-modules-create"
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description: |-
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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, creating a module is a piece of cake.
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---
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# Creating Modules
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Creating modules in Terraform is easy. You may want to do this to better
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organize your code, to make a reusable component, or just to learn more about
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Terraform. For any reason, if you already know the basics of Terraform,
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creating a module is a piece of cake.
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Modules in Terraform are just folders with Terraform files. In fact,
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when you run `terraform apply`, the current working directory holding
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the Terraform files you're applying comprise what is called the
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_root module_. It itself is a valid module.
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Therefore, you can enter the source of any module, run `terraform apply`,
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and expect it to work (assuming you satisfy the required variables, if any).
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## An Example
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Within a folder containing Terraform configurations, create a subfolder
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"child". In this subfolder, make one empty "main.tf" file. Then, back in
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the root folder containing the "child" folder, add this to one of the
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Terraform files:
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```
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module "child" {
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source = "./child"
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}
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```
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This will work. You've created your first module! You can add resources
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to the child module to see how that interaction works.
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Note: Prior to running the above, you'll have to run
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[the get command](/docs/commands/get.html) for Terraform to sync
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your modules. This should be instant since the module is just a local path.
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## Inputs/Outputs
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To make modules more useful than simple isolated containers of Terraform
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configurations, modules can be configured and also have outputs that can be
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consumed by the configuration using the module.
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Inputs of a module are [variables](/docs/configuration/variables.html)
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and outputs are [outputs](/docs/configuration/outputs.html). There is no
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special syntax to define these, they're defined just like any other
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variables or outputs.
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In the "child" module we created above, add the following:
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```
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variable "memory" {}
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output "received" {
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value = "${var.memory}"
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}
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```
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This will create a required variable "memory" and then an output "received"
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that will simply be the value of the memory variable.
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You can then configure the module and use the output like so:
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```
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module "child" {
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source = "./child"
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memory = "1G"
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}
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output "child_memory" {
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value = "${module.child.received}"
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}
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```
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If you run `apply`, you'll again see that this works.
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And that is all there is to it. Variables and outputs are used to configure
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modules and provide results. Resources within a module are isolated,
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and the whole thing is managed as a single unit.
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## Paths and Embedded Files
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It is sometimes useful to embed files within the module that aren't
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Terraform configuration files, such as a script to provision a resource
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or a file to upload.
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In these cases, you can't use a relative path, since paths in Terraform
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are generally relative to the working directory that Terraform was executed
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from. Instead, you want to use a module-relative path. To do this, use
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the [path interpolated variables](/docs/configuration/interpolation.html).
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An example is shown below:
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```
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resource "aws_instance" "server" {
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...
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provisioner "remote-exec" {
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script = "${path.module}/script.sh"
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}
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}
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```
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In the above, we use `${path.module}` to get a module-relative path. This
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is usually what you'll want in any case.
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## Nested Modules
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You can use a module within a module just like you would anywhere else.
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This module will be hidden from the root user, so you'll have re-expose any
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variables if you need to, as well as outputs.
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The [get command](/docs/commands/get.html) will automatically get all
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nested modules as well.
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You don't have to worry about conflicting versions of modules, since
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Terraform builds isolated subtrees of all dependencies. For example,
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one module might use version 1.0 of module "foo" and another module
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might use version 2.0 of module "foo", and this would all work fine
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within Terraform since the modules are created separately.
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