206 lines
6.0 KiB
Markdown
206 lines
6.0 KiB
Markdown
---
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layout: "intro"
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page_title: "Input Variables"
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sidebar_current: "gettingstarted-variables"
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description: |-
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You now have enough Terraform knowledge to create useful configurations, but we're still hardcoding access keys, AMIs, etc. To become truly shareable and committable to version control, we need to parameterize the configurations. This page introduces input variables as a way to do this.
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---
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# Input Variables
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You now have enough Terraform knowledge to create useful
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configurations, but we're still hardcoding access keys,
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AMIs, etc. To become truly shareable and committable to version
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control, we need to parameterize the configurations. This page
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introduces input variables as a way to do this.
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## Defining Variables
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Let's first extract our access key, secret key, and region
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into a few variables. Create another file `variables.tf` with
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the following contents. Note that the file can be named anything,
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since Terraform loads all files ending in `.tf` in a directory.
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```
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variable "access_key" {}
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variable "secret_key" {}
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variable "region" {
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default = "us-east-1"
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}
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```
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This defines three variables within your Terraform configuration.
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The first two have empty blocks `{}`. The third sets a default. If
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a default value is set, the variable is optional. Otherwise, the
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variable is required. If you run `terraform plan` now, Terraform will
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error since the required variables are not set.
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## Using Variables in Configuration
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Next, replace the AWS provider configuration with the following:
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```
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provider "aws" {
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access_key = "${var.access_key}"
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secret_key = "${var.secret_key}"
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region = "${var.region}"
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}
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```
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This uses more interpolations, this time prefixed with `var.`. This
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tells Terraform that you're accessing variables. This configures
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the AWS provider with the given variables.
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## Assigning Variables
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There are multiple ways to assign variables. Below is also the order
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in which variable values are chosen. If they're found in an option first
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below, then the options below are ignored.
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**UI Input:** If you execute `terraform plan` or apply without doing
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anything, Terraform will ask you to input the variables interactively.
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These variables are not saved, but provides a nice user experience for
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getting started with Terraform.
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**Command-line flags:** You can set it directly on the command-line with the
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`-var` flag. Any command in Terraform that inspects the configuration
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accepts this flag, such as `apply`, `plan`, and `refresh`:
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```
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$ terraform plan \
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-var 'access_key=foo' \
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-var 'secret_key=bar'
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...
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```
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Once again, setting variables this way will not save them, and they'll
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have to be input repeatedly as commands are executed.
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**From a file:** To persist variable values, create
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a file and assign variables within this file. Create a file named
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"terraform.tfvars" with the following contents:
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```
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access_key = "foo"
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secret_key = "bar"
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```
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If a "terraform.tfvars" file is present in the current directory,
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Terraform automatically loads it to populate variables. If the file is
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named something else, you can use the `-var-file` flag directly to
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specify a file. These files are the same syntax as Terraform configuration
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files. And like Terraform configuration files, these files can also be JSON.
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**From environment variables:** Terraform will read environment variables
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in the form of `TF_VAR_name` to find the value for a variable. For example,
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the `TF_VAR_access_key` variable can be set to set the `access_key` variable.
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We recommend using the "terraform.tfvars" file, and ignoring it from
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version control.
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<a id="mappings"></a>
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## Mappings
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We've replaced our sensitive strings with variables, but we still
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are hardcoding AMIs. Unfortunately, AMIs are specific to the region
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that is in use. One option is to just ask the user to input the proper
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AMI for the region, but Terraform can do better than that with
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_mappings_.
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Mappings are a way to create variables that are lookup tables. An example
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will show this best. Let's extract our AMIs into a mapping and add
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support for the "us-west-2" region as well:
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```
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variable "amis" {
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default = {
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us-east-1 = "ami-aa7ab6c2"
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us-west-2 = "ami-23f78e13"
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}
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}
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```
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A variable becomes a mapping when it has a default value that is a
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map like above. There is no way to create a required map.
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Then, replace the "aws\_instance" with the following:
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```
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resource "aws_instance" "example" {
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ami = "${lookup(var.amis, var.region)}"
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instance_type = "t1.micro"
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}
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```
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This introduces a new type of interpolation: a function call. The
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`lookup` function does a dynamic lookup in a map for a key. The
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key is `var.region`, which specifies that the value of the region
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variables is the key.
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While we don't use it in our example, it is worth noting that you
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can also do a static lookup of a mapping directly with
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`${var.amis.us-east-1}`.
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<a id="assigning-mappings"></a>
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## Assigning Mappings
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We set defaults above, but mappings can also be set using the `-var` and
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`-var-file` values. For example, if the user wanted to specify an alternate AMI
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for us-east-1:
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```
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$ terraform plan -var 'amis.us-east-1=foo'
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...
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```
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**Note**: even if every key will be assigned as input, the variable must be
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established as a mapping by setting its default to `{}`.
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Here is an example of setting a mapping's keys from a file. Starting with these
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variable definitions:
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```
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variable "region" {}
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variable "amis" {
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default = {}
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}
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```
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You can specify keys in a `terraform.tfvars` file:
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```
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amis.us-east-1 = "ami-abc123"
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amis.us-west-2 = "ami-def456"
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```
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And access them via `lookup()`:
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```
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output "ami" {
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value = "${lookup(var.amis, var.region)}
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}
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```
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Like so:
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```
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$ terraform apply -var region=us-west-2
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Apply complete! Resources: 0 added, 0 changed, 0 destroyed.
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Outputs:
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ami = ami-def456
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```
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## Next
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Terraform provides variables for parameterizing your configurations.
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Mappings let you build lookup tables in cases where that makes sense.
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Setting and using variables is uniform throughout your configurations.
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In the next section, we'll take a look at
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[output variables](/intro/getting-started/outputs.html) as a mechanism
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to expose certain values more prominently to the Terraform operator.
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