270 lines
11 KiB
Markdown
270 lines
11 KiB
Markdown
---
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layout: "intro"
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page_title: "Modules"
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sidebar_current: "gettingstarted-modules"
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description: |-
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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.
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---
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# Modules
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Up to this point, we've been configuring Terraform by editing Terraform
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configurations directly. As our infrastructure grows, this practice has a few
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key problems: a lack of organization, a lack of reusability, and difficulties
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in management for teams.
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_Modules_ in Terraform are self-contained packages of Terraform configurations
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that are managed as a group. Modules are used to create reusable components,
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improve organization, and to treat pieces of infrastructure as a black box.
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This section of the getting started will cover the basics of using modules.
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Writing modules is covered in more detail in the
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[modules documentation](/docs/modules/index.html).
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~> **Warning!** The examples on this page are _**not** eligible_ for
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[the AWS free tier](https://aws.amazon.com/free/). Do not try the examples
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on this page unless you're willing to spend a small amount of money.
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## Using Modules
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If you have any instances running from prior steps in the getting
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started guide, use `terraform destroy` to destroy them, and remove all
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configuration files.
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The [Terraform Registry](https://registry.terraform.io/) includes a directory
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of ready-to-use modules for various common purposes, which can serve as
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larger building-blocks for your infrastructure.
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In this example, we're going to use
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[the Consul Terraform module for AWS](https://registry.terraform.io/modules/hashicorp/consul/aws),
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which will set up a complete [Consul](https://www.consul.io) cluster.
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This and other modules can be found via the search feature on the Terraform
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Registry site.
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Create a configuration file with the following contents:
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```hcl
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provider "aws" {
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access_key = "AWS ACCESS KEY"
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secret_key = "AWS SECRET KEY"
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region = "us-east-1"
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}
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module "consul" {
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source = "hashicorp/consul/aws"
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num_servers = "3"
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}
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```
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The `module` block begins with the example given on the Terraform Registry
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page for this module, telling Terraform to create and manage this module.
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This is similar to a `resource` block: it has a name used within this
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configuration -- in this case, `"consul"` -- and a set of input values
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that are listed in
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[the module's "Inputs" documentation](https://registry.terraform.io/modules/hashicorp/consul/aws?tab=inputs).
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(Note that the `provider` block can be omitted in favor of environment
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variables. See the [AWS Provider docs](/docs/providers/aws/index.html)
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for details. This module requires that your AWS account has a default VPC.)
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The `source` attribute is the only mandatory argument for modules. It tells
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Terraform where the module can be retrieved. Terraform automatically
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downloads and manages modules for you.
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In this case, the module is retrieved from the official Terraform Registry.
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Terraform can also retrieve modules from a variety of sources, including
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private module registries or directly from Git, Mercurial, HTTP, and local
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files.
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The other attributes shown are inputs to our module. This module supports many
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additional inputs, but all are optional and have reasonable values for
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experimentation.
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After adding a new module to configuration, it is necessary to run (or re-run)
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`terraform init` to obtain and install the new module's source code:
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```
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$ terraform init
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# ...
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```
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By default, this command does not check for new module versions that may be
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available, so it is safe to run multiple times. The `-upgrade` option will
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additionally check for any newer versions of existing modules and providers
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that may be available.
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## Apply Changes
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With the Consul module (and its dependencies) installed, we can now apply
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these changes to create the resources described within.
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If you run `terraform apply`, you will see a large list of all of the
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resources encapsulated in the module. The output is similar to what we
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saw when using resources directly, but the resource names now have
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module paths prefixed to their names, like in the following example:
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```
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+ module.consul.module.consul_clients.aws_autoscaling_group.autoscaling_group
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id: <computed>
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arn: <computed>
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default_cooldown: <computed>
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desired_capacity: "6"
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force_delete: "false"
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health_check_grace_period: "300"
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health_check_type: "EC2"
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launch_configuration: "${aws_launch_configuration.launch_configuration.name}"
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max_size: "6"
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metrics_granularity: "1Minute"
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min_size: "6"
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name: <computed>
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protect_from_scale_in: "false"
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tag.#: "2"
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tag.2151078592.key: "consul-clients"
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tag.2151078592.propagate_at_launch: "true"
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tag.2151078592.value: "consul-example"
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tag.462896764.key: "Name"
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tag.462896764.propagate_at_launch: "true"
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tag.462896764.value: "consul-example-client"
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termination_policies.#: "1"
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termination_policies.0: "Default"
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vpc_zone_identifier.#: "6"
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vpc_zone_identifier.1880739334: "subnet-5ce4282a"
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vpc_zone_identifier.3458061785: "subnet-16600f73"
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vpc_zone_identifier.4176925006: "subnet-485abd10"
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vpc_zone_identifier.4226228233: "subnet-40a9b86b"
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vpc_zone_identifier.595613151: "subnet-5131b95d"
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vpc_zone_identifier.765942872: "subnet-595ae164"
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wait_for_capacity_timeout: "10m"
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```
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The `module.consul.module.consul_clients` prefix shown above indicates
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not only that the resource is from the `module "consul"` block we wrote,
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but in fact that this module has its own `module "consul_clients"` block
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within it. Modules can be nested to decompose complex systems into
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manageable components.
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The full set of resources created by this module includes an autoscaling group,
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security groups, IAM roles and other individual resources that all support
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the Consul cluster that will be created.
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Note that as we warned above, the resources created by this module are
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not eligible for the AWS free tier and so proceeding further will have some
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cost associated. To proceed with the creation of the Consul cluster, type
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`yes` at the confirmation prompt.
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```
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# ...
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module.consul.module.consul_clients.aws_security_group.lc_security_group: Creating...
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description: "" => "Security group for the consul-example-client launch configuration"
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egress.#: "" => "<computed>"
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ingress.#: "" => "<computed>"
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name: "" => "<computed>"
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name_prefix: "" => "consul-example-client"
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owner_id: "" => "<computed>"
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revoke_rules_on_delete: "" => "false"
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vpc_id: "" => "vpc-22099946"
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# ...
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Apply complete! Resources: 34 added, 0 changed, 0 destroyed.
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```
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After several minutes and many log messages about all of the resources
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being created, you'll have a three-server Consul cluster up and running.
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Without needing any knowledge of how Consul works, how to install Consul,
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or how to form a Consul cluster, you've created a working cluster in just
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a few minutes.
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## Module Outputs
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Just as the module instance had input arguments such as `num_servers` above,
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module can also produce _output_ values, similar to resource attributes.
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[The module's outputs reference](https://registry.terraform.io/modules/hashicorp/consul/aws?tab=outputs)
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describes all of the different values it produces. Overall, it exposes the
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id of each of the resources it creates, as well as echoing back some of the
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input values.
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One of the supported outputs is called `asg_name_servers`, and its value
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is the name of the auto-scaling group that was created to manage the Consul
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servers.
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To reference this, we'll just put it into our _own_ output value. This
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value could actually be used anywhere: in another resource, to configure
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another provider, etc.
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Add the following to the end of the existing configuration file created
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above:
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```hcl
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output "consul_server_asg_name" {
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value = "${module.consul.asg_name_servers}"
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}
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```
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The syntax for referencing module outputs is `${module.NAME.OUTPUT}`, where
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`NAME` is the module name given in the header of the `module` configuration
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block and `OUTPUT` is the name of the output to reference.
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If you run `terraform apply` again, Terraform will make no changes to
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infrastructure, but you'll now see the "consul\_server\_asg\_name" output with
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the name of the created auto-scaling group:
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```
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# ...
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Apply complete! Resources: 0 added, 0 changed, 0 destroyed.
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Outputs:
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consul_server_asg_name = tf-asg-2017103123350991200000000a
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```
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If you look in the Auto-scaling Groups section of the EC2 console you should
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find an autoscaling group of this name, and from there find the three
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Consul servers it is running. (If you can't find it, make sure you're looking
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in the right region!)
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## Destroy
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Just as with top-level resources, we can destroy the resources created by
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the Consul module to avoid ongoing costs:
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```
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$ terraform destroy
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# ...
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Terraform will perform the following actions:
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- module.consul.module.consul_clients.aws_autoscaling_group.autoscaling_group
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- module.consul.module.consul_clients.aws_iam_instance_profile.instance_profile
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- module.consul.module.consul_clients.aws_iam_role.instance_role
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# ...
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```
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As usual, Terraform describes all of the actions it will take. In this case,
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it plans to destroy all of the resources that were created by the module.
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Type `yes` to confirm and, after a few minutes and even more log output,
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all of the resources should be destroyed:
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```
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Destroy complete! Resources: 34 destroyed.
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```
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With all of the resources destroyed, you can delete the configuration file
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we created above. We will not make any further use of it, and so this avoids
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the risk of accidentally re-creating the Consul cluster.
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## Next
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For more information on modules, the types of sources supported, how
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to write modules, and more, read the in-depth
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[module documentation](/docs/modules/index.html).
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Next, we learn about [Terraform's remote collaboration features](/intro/getting-started/remote.html).
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