terraform/website/docs/internals/resource-addressing.html.markdown

layout	page_title	sidebar_current	description
docs	Internals: Resource Address	docs-internals-resource-addressing	Resource addressing is used to target specific resources in a larger infrastructure.

Resource Addressing

A Resource Address is a string that references a specific resource in a larger infrastructure. An address is made up of two parts:

[module path][resource spec]

Module path:

A module path addresses a module within the tree of modules. It takes the form:

module.A.module.B.module.C...

Multiple modules in a path indicate nesting. If a module path is specified without a resource spec, the address applies to every resource within the module. If the module path is omitted, this addresses the root module.

Resource spec:

A resource spec addresses a specific resource in the config. It takes the form:

resource_type.resource_name[resource index]

• resource_type - Type of the resource being addressed.
• resource_name - User-defined name of the resource.
• [resource index] - an optional index into a resource with multiple instances, surrounded by square brace characters ([ and ]).

-> In Terraform v0.12 and later, a resource spec without a module path prefix matches only resources in the root module. In earlier versions, a resource spec without a module path prefix will match resources with the same type and name in any descendent module.

Resource index:

• [N] where N is a 0-based numerical index into a resource with multiple instances specified by the count meta-argument. Omitting an index when addressing a resource where count > 1 means that the address references all instances.
• ["INDEX"] where INDEX is a alphanumerical key index into a resource with multiple instances specified by the for_each meta-argument.

Examples

count Example

Given a Terraform config that includes:

resource "aws_instance" "web" {
  # ...
  count = 4
}

An address like this:

aws_instance.web[3]

Refers to only the last instance in the config, and an address like this:

aws_instance.web

Refers to all four "web" instances.

for_each Example

Given a Terraform config that includes:

resource "aws_instance" "web" {
  # ...
  for_each = {
    "terraform": "value1",
    "resource":  "value2",
    "indexing":  "value3",
    "example":   "value4",
  }
}

An address like this:

aws_instance.web["example"]

Refers to only the "example" instance in the config, and an address like this:

aws_instance.web[*]

Refers to all four "web" instances.