Argument

Q: How deeply does Terraform in Depth: Infrastructure as Code with Terraform and OpenTofu cover argument?

Defines assignment syntax and uniqueness, then distinguishes arguments from repeatable subblocks and exported attributes; defers complex expressions.

As explained in Terraform in Depth: Infrastructure as Code with Terraform and OpenTofu

A Terraform resource argument is a named value in a resource configuration that specifies an attribute of the represented infrastructure object.

To configure an AWS instance, put named values inside its resource block: `ami` selects an image, `subnet_id` identifies a subnet, and `instance_type` sets the instance type. Each is an argument: a `name = value` assignment that changes how the block behaves. The resource’s type determines which arguments it accepts. section 2.5.1 section 2.2.3

Listing 2.12 Terraform resource with arguments

resource "aws_instance" "hello_world" {
  ami           = data.aws_ami.ubuntu.id          #1
  subnet_id     = data.aws_subnets.default.ids[0] #1
  instance_type = var.instance_type               #1
}

The instance’s argument values come from three places: an AMI data source, a subnet data source, and an input variable. An argument value can be a Terraform expression, not just a literal. section 2.2.3

An argument name can appear only once in a block. Do not confuse an object-valued argument, which has an equals sign, with a nested subblock, which does not. Subblocks can normally repeat—for example, a data source can use several `filter` subblocks. section 2.2 section 2.2.3

Arguments also become accessible attributes, so another block can refer to a configured value. A resource may expose additional read-only attributes after a plan or apply; values inside subblocks are not exposed as attributes. Ordinary resource arguments configure infrastructure, while meta arguments tell Terraform how to process a block during planning. Some meta arguments require literal values or values known at plan time. section 2.2.4 section 2.7

How Terraform in Depth: Infrastructure as Code with Terraform and OpenTofu covers it

Cover of Terraform in Depth: Infrastructure as Code with Terraform and OpenTofu

liveBook manning.com

Read Terraform in Depth: Infrastructure as Code with Terraform and OpenTofu on liveBook Get the book at manning.com

Related concepts

local valueused by · A Terraform local value is a module-scoped named expression whose reusable result can be referenced within the configuration without being exposed as an external input or output.
terraform blockpart of · A terraform block is a Terraform configuration block that specifies settings for Terraform itself, including provider dependencies.
blockpart of · A block is a Terraform HCL construct that defines a concrete configuration or infrastructure item and can contain arguments, attributes, and nested blocks.
meta argumentincludes · A meta argument is a built-in Terraform argument that controls how Terraform processes a block rather than configuring the underlying infrastructure.
resource typeconfigures · A resource type is a classification identifying the kind of resource represented and the properties, arguments, or capabilities associated with it.
attributekind of · An attribute is a named property, value, or piece of information associated with an entity, object, or program element.

This explainer was generated by Manning's knowledge graph from the text of Terraform in Depth: Infrastructure as Code with Terraform and OpenTofu. The section links point to the parts of the book it draws on.