119 lines
4.1 KiB
Markdown
119 lines
4.1 KiB
Markdown
---
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layout: "language"
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page_title: "Overview - Configuration Language"
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---
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# Terraform Language Documentation
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This is the documentation for Terraform's configuration language. It is relevant
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to users of [Terraform CLI](/docs/cli/index.html),
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[Terraform Cloud](/docs/cloud/index.html), and
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[Terraform Enterprise](/docs/enterprise/index.html).
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> **Hands-on:** Try the [Terraform: Get Started](https://learn.hashicorp.com/collections/terraform/aws-get-started?utm_source=WEBSITE&utm_medium=WEB_IO&utm_offer=ARTICLE_PAGE&utm_content=DOCS) collection on HashiCorp Learn.
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_The Terraform language is Terraform's primary user interface._ In every edition
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of Terraform, a configuration written in the Terraform language is always at the
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heart of the workflow.
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## About the Terraform Language
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The main purpose of the Terraform language is declaring
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[resources](/docs/language/resources/index.html), which represent infrastructure objects. All other
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language features exist only to make the definition of resources more flexible
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and convenient.
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A _Terraform configuration_ is a complete document in the Terraform language
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that tells Terraform how to manage a given collection of infrastructure. A
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configuration can consist of multiple files and directories.
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The syntax of the Terraform language consists of only a few basic elements:
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```hcl
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resource "aws_vpc" "main" {
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cidr_block = var.base_cidr_block
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}
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<BLOCK TYPE> "<BLOCK LABEL>" "<BLOCK LABEL>" {
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# Block body
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<IDENTIFIER> = <EXPRESSION> # Argument
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}
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```
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- _Blocks_ are containers for other content and usually represent the
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configuration of some kind of object, like a resource. Blocks have a
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_block type,_ can have zero or more _labels,_ and have a _body_ that contains
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any number of arguments and nested blocks. Most of Terraform's features are
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controlled by top-level blocks in a configuration file.
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- _Arguments_ assign a value to a name. They appear within blocks.
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- _Expressions_ represent a value, either literally or by referencing and
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combining other values. They appear as values for arguments, or within other
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expressions.
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The Terraform language is declarative, describing an intended goal rather than
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the steps to reach that goal. The ordering of blocks and the files they are
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organized into are generally not significant; Terraform only considers implicit
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and explicit relationships between resources when determining an order of
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operations.
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### Example
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The following example describes a simple network topology for Amazon Web
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Services, just to give a sense of the overall structure and syntax of the
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Terraform language. Similar configurations can be created for other virtual
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network services, using resource types defined by other providers, and a
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practical network configuration will often contain additional elements not
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shown here.
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```hcl
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terraform {
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required_providers {
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aws = {
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source = "hashicorp/aws"
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version = "~> 1.0.4"
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}
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}
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}
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variable "aws_region" {}
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variable "base_cidr_block" {
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description = "A /16 CIDR range definition, such as 10.1.0.0/16, that the VPC will use"
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default = "10.1.0.0/16"
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}
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variable "availability_zones" {
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description = "A list of availability zones in which to create subnets"
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type = list(string)
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}
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provider "aws" {
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region = var.aws_region
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}
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resource "aws_vpc" "main" {
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# Referencing the base_cidr_block variable allows the network address
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# to be changed without modifying the configuration.
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cidr_block = var.base_cidr_block
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}
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resource "aws_subnet" "az" {
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# Create one subnet for each given availability zone.
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count = length(var.availability_zones)
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# For each subnet, use one of the specified availability zones.
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availability_zone = var.availability_zones[count.index]
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# By referencing the aws_vpc.main object, Terraform knows that the subnet
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# must be created only after the VPC is created.
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vpc_id = aws_vpc.main.id
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# Built-in functions and operators can be used for simple transformations of
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# values, such as computing a subnet address. Here we create a /20 prefix for
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# each subnet, using consecutive addresses for each availability zone,
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# such as 10.1.16.0/20 .
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cidr_block = cidrsubnet(aws_vpc.main.cidr_block, 4, count.index+1)
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}
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```
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