128 lines
3.4 KiB
Markdown
128 lines
3.4 KiB
Markdown
---
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layout: "docs"
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page_title: "Internals: Resource Address"
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sidebar_current: "docs-internals-resource-addressing"
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description: |-
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Resource addressing is used to target specific resources in a larger
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infrastructure.
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---
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# Resource Addressing
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A __Resource Address__ is a string that references a specific resource in a
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larger infrastructure. An address is made up of two parts:
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```
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[module path][resource spec]
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```
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## Module path
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A module path addresses a module within the tree of modules. It takes the form:
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```
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module.module_name[module index]
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```
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* `module` - Module keyword indicating a child module (non-root). Multiple `module`
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keywords in a path indicate nesting.
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* `module_name` - User-defined name of the module.
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* `[module index]` - (Optional) [Index](#index-values-for-modules-and-resources) into a
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module with multiple instances, surrounded by square brace characters (`[` and `]`).
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An address without a resource spec, i.e. `module.foo` applies to every resource within
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the module if a single module, or all instances of a module if a module has multiple instances.
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To address all resources of a particular module instance, include the module index in the address,
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such as `module.foo[0]`.
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If the module path is omitted, the address applies to the root module.
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An example of the `module` keyword delineating between two modules that have multiple instances:
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```
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module.foo[0].module.bar["a"]
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```
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-> Module index only applies to modules in Terraform v0.13 or later, as in earlier
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versions of Terraform, a module could not have multiple instances.
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## Resource spec
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A resource spec addresses a specific resource in the config. It takes the form:
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```
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resource_type.resource_name[resource index]
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```
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* `resource_type` - Type of the resource being addressed.
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* `resource_name` - User-defined name of the resource.
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* `[resource index]` - (Optional) [Index](#index-values-for-modules-and-resources)
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into a resource with multiple instances, surrounded by square brace characters (`[` and `]`).
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-> In Terraform v0.12 and later, a resource spec without a module path prefix
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matches only resources in the root module. In earlier versions, a resource spec
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without a module path prefix will match resources with the same type and name
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in any descendent module.
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## Index values for Modules and Resources
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The following specifications apply to index values on modules and resources with multiple instances:
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* `[N]` where `N` is a `0`-based numerical index into a resource with multiple
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instances specified by the `count` meta-argument. Omitting an index when
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addressing a resource where `count > 1` means that the address references
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all instances.
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* `["INDEX"]` where `INDEX` is a alphanumerical key index into a resource with
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multiple instances specified by the `for_each` meta-argument.
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## Examples
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### count Example
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Given a Terraform config that includes:
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```hcl
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resource "aws_instance" "web" {
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# ...
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count = 4
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}
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```
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An address like this:
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```
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aws_instance.web[3]
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```
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Refers to only the last instance in the config, and an address like this:
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```
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aws_instance.web
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```
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Refers to all four "web" instances.
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### for_each Example
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Given a Terraform config that includes:
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```hcl
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resource "aws_instance" "web" {
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# ...
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for_each = {
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"terraform": "value1",
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"resource": "value2",
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"indexing": "value3",
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"example": "value4",
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}
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}
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```
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An address like this:
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```
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aws_instance.web["example"]
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```
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Refers to only the "example" instance in the config.
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