terraform/website/source/intro/getting-started/modules.html.md

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intro	Modules	gettingstarted-modules

Modules

Up to this point, we've been configuring Terraform by editing Terraform configurations directly. As our infrastructure grows, this practice has a few key problems: a lack of organization, a lack of reusability, and difficulties in management for teams.

Modules in Terraform are self-contained packages of Terraform configurations that are managed as a group. Modules are used to create reusable components, improve organization, and to treat pieces of infrastructure as a black box.

This section of the getting started will cover the basics of using modules. Writing modules is covered in more detail in the modules documentation.

Warning: The examples on this page are not eligible for the AWS free-tier. Do not execute the examples on this page unless you're willing to spend a small amount of money.

Using Modules

If you have any instances running from prior steps in the getting started guide, use terraform destroy to destroy them, and remove all configuration files.

As an example, we're going to use the Consul Terraform module which will setup a complete Consul cluster for us.

Create a configuration file with the following contents:

module "consul" {
	source = "github.com/hashicorp/consul/terraform/aws"

	key_name = "AWS SSH KEY NAME"
	key_path = "PATH TO ABOVE PRIVATE KEY"
	region = "AWS REGION"
	servers = "3"
}

The module block tells Terraform to create and manage a module. It is very similar to the resource block. It has a logical name -- in this case "consul" -- and a set of configurations.

The source configuration is the only mandatory key for modules. It tells Terraform where the module can be retrieved. Terraform automatically downloads and manages modules for you. For our example, we're getting the module directly from GitHub. Terraform can retrieve modules from a variety of sources including Git, Mercurial, HTTP, and file paths.

The other configurations are parameters to our module. Please fill them in with the proper values.

Planning and Apply Modules

With the modules downloaded, we can now plan and apply it. If you run terraform plan, you should see output similar to below:

$ terraform plan
TODO

As you can see, the module is treated like a black box. In the plan, Terraform shows the module managed as a whole. It does not show what resources within the module will be created. If you care, you can see that by specifying a -module-depth=-1 flag.

Next, run terraform apply to create the module. Note that as we warned above, the resources this module creates are outside of the AWS free tier, so this will have some cost associated with it.

$ terraform apply
TODO

After a few minutes, you'll have a three server Consul cluster up and running! Without any knowledge of how Consul works, how to install Consul, or how to configure Consul into a cluster, you've created a real cluster in just minutes.

Module Outputs

Just as we parameterized the module with configurations such as servers above, modules can also output information (just like a resource).

You'll have to reference the module's code or documentation to know what outputs it supports for now, but for this guide we'll just tell you that the Consul module has an output named server_address that has the address of one of the Consul servers that was setup.

To reference this, we'll just put it into our own output variable. But this value could be used anywhere: in another resource, to configure another provider, etc.

output "consul_address" {
	value = "${module.consul.server_address}"
}

The syntax for referencing module outputs should be very familiar. The syntax is ${module.NAME.ATTRIBUTE}. The NAME is the logical name we assigned earlier, and the ATTRIBUTE is the output attribute.

If you run terraform apply again, Terraform should make no changes, but you'll now see the "consul_address" output with the address of our Consul server.

Next

For more information on modules, the types of sources supported, how to write modules, and more, read the in depth module documentation.

We've now concluded the getting started guide, however there are a number of next steps to get started with Terraform.