» Resource Addressing

A resource address is a string that identifies zero or more resource instances in your overall configuration.

An address is made up of two parts:

[module path][resource spec]

In some contexts Terraform might allow for an incomplete resource address that only refers to a module as a whole, or that omits the index for a multi-instance resource. In those cases, the meaning depends on the context, so you'll need to refer to the documentation for the specific feature you are using which parses resource addresses.

» Module path

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

module.module_name[module index]

module - Module keyword indicating a child module (non-root). Multiple module keywords in a path indicate nesting.
module_name - User-defined name of the module.
[module index] - (Optional) Index to select an instance from a module call that has multiple instances, surrounded by square bracket characters ([ and ]).

An address without a resource spec, i.e. module.foo applies to every resource within the module if a single module, or all instances of a module if a module has multiple instances. To address all resources of a particular module instance, include the module index in the address, such as module.foo[0].

If the module path is omitted, the address applies to the root module.

An example of the module keyword delineating between two modules that have multiple instances:

module.foo[0].module.bar["a"]

Module index only applies to modules in Terraform v0.13 or later. In earlier versions of Terraform, a module could not have multiple instances.

» Resource spec

A resource spec addresses a specific resource instance in the selected module. It has the following syntax:

resource_type.resource_name[instance index]

resource_type - Type of the resource being addressed.
resource_name - User-defined name of the resource.
[instance index] - (Optional) Index to select an instance from a resource that has multiple instances, surrounded by square bracket 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 would match resources with the same type and name in any descendent module.

» Index values for Modules and Resources

The following specifications apply to index values on modules and resources with multiple instances:

[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