137 lines
4.5 KiB
Markdown
137 lines
4.5 KiB
Markdown
---
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layout: "docs"
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page_title: "Using Modules"
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sidebar_current: "docs-modules-usage"
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description: Using modules in Terraform is very similar to defining resources.
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---
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# Module Usage
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Using modules in Terraform is very similar to defining resources:
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```
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module "consul" {
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source = "github.com/hashicorp/consul/terraform/aws"
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servers = 3
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}
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```
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You can view the full documentation for the syntax of configuring
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modules [here](/docs/configuration/modules.html).
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As you can see, it is very similar to defining resources, with the exception
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that we don't specify a type, and just a name. This name can be used elsewhere
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in the configuration to reference the module and its variables.
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The existence of the above configuration will tell Terraform to create
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the resources in the "consul" module which can be found on GitHub with the
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given URL. Just like a resource, the module configuration can be deleted
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to remove the module.
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## Source
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The only required configuration key is the `source` parameter. The value of
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this tells Terraform where the module can be downloaded, updated, etc.
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Terraform comes with support for a variety of module sources. These
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are documented on a [separate page](/docs/modules/sources.html).
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Prior to running any command such as `plan` with a configuration that
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uses modules, you'll have to [get](/docs/commands/get.html) the modules.
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This is done using the [get command](/docs/commands/get.html).
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```
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$ terraform get
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...
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```
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This command will download the modules if they haven't been already.
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By default, the command will not check for updates, so it is safe (and fast)
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to run multiple times. You can use the `-update` flag to check and download
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updates.
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## Configuration
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The parameters used to configure modules, such as the `servers` parameter
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above, map directly to [variables](/docs/configuration/variables.html) within
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the module itself. Therefore, you can quickly discover all the configuration
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for a module by inspecting the source of it very easily.
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Additionally, because these map directly to variables, they're always simple
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key/value pairs. Modules can't have complex variable inputs.
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## Dealing with parameters of the list type
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Variables are currently unable to hold the list type. Sometimes, though, it's
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desirable to parameterize a module's resource with an attribute that is of the
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list type, for example `aws_instance.security_groups`.
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Until a future release broadens the functionality of variables to include list
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types, the way to work around this limitation is to pass a delimited string as
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a module parameter, and then "unpack" that parameter using
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[`split`](/docs/configuration/interpolation.html) interpolation function within
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the module definition.
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Depending on the resource parameter in question, you may have to
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indicate that the unpacked string is actually a list by using list notation.
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For example:
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```
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resource_param = ["${split(",", var.CSV_STRING)}"]
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```
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## Outputs
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Modules can also specify their own [outputs](/docs/configuration/outputs.html).
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These outputs can be referenced in other places in your configuration.
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For example:
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```
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resource "aws_instance" "client" {
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ami = "ami-408c7f28"
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instance_type = "t1.micro"
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availability_zone = "${module.consul.server_availability_zone}"
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}
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```
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This purposely is very similar to accessing resource attributes. But instead
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of mapping to a resource, the variable in this case maps to an output of
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a module.
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Just like resources, this will create a dependency from the `aws_instance.client`
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resource to the module, so the module will be built first.
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## Plans and Graphs
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With modules, commands such as the [plan command](/docs/commands/plan.html)
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and
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[graph command](/docs/commands/graph.html) will expand modules by default. You
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can use the `-module-depth` parameter to limit the graph.
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For example, with a configuration similar to what we've built above, here
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is what the graph output looks like by default:
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<div class="center">
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</div>
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But if we set `-module-depth=0`, the graph will look like this:
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<div class="center">
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</div>
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Other commands work similarly with modules. Note that the `-module-depth`
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flag is purely a formatting flag; it doesn't affect what modules are created
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or not.
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## Tainting resources within a module
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The [taint command](/docs/commands/taint.html) can be used to _taint_
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specific resources within a module:
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```
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terraform taint -module=salt_master aws_instance.salt_master
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```
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It is not (yet) possible to taint an entire module.
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