Add docs for the conditional enabled lifecycle attribute (#3380)

Signed-off-by: Diogenes Fernandes <diofeher@gmail.com>
Co-authored-by: Martin Atkins <mart@degeneration.co.uk>
Co-authored-by: Andrei Ciobanu <andrei.ciobanu@opentofu.org>

website/docs/language/data-sources/index.mdx

@@ -165,8 +165,23 @@ as defined for managed resources, with the same syntax and behavior.
 
 ## Lifecycle Customizations
 
-Data resources do not have any customization settings available
-for their lifecycle. However, the `lifecycle` block is reserved for future versions.
+Data resources support a `lifecycle` block that includes the [`enabled`](../../language/meta-arguments/enabled.mdx) argument to conditionally enable or disable the data resource.
+
+```hcl
+variable "fetch_ami_data" {
+  type    = bool
+  default = true
+}
+
+data "aws_ami" "example" {
+  most_recent = true
+  owners      = ["self"]
+
+  lifecycle {
+    enabled = var.fetch_ami_data
+  }
+}
+```
 
 ## Example
 
@@ -214,9 +229,9 @@ resource "aws_instance" "web" {
 
 ## Meta-Arguments
 
-As data sources are essentially a read only subset of resources, they also
-support the same [meta-arguments](../../language/resources/syntax.mdx#meta-arguments) of resources
-with the exception of the
+As data sources are essentially a read-only subset of resources, they also
+support the same [meta-arguments](../../language/resources/syntax.mdx#meta-arguments) as resources
+with the exception of a slightly simpler version of the
 [`lifecycle` configuration block](../../language/meta-arguments/lifecycle.mdx).
 
 ### Non-Default Provider Configurations

website/docs/language/ephemerality/ephemeral-resources.mdx

@@ -40,7 +40,8 @@ Besides the attributes in the schema of an ephemeral resource, the block support
 * [`for_each`](../../language/meta-arguments/for_each.mdx)
 * [`provider`](../../language/meta-arguments/resource-provider.mdx)
 * [`lifecycle`](../../language/meta-arguments/lifecycle.mdx)
-  * Only [`precondition` and `postcondition`](../../language/expressions/custom-conditions.mdx#preconditions-and-postconditions)
+  * [`enabled`](../../language/meta-arguments/enabled.mdx) for conditional enabling
+  * [`precondition` and `postcondition`](../../language/expressions/custom-conditions.mdx#preconditions-and-postconditions)
 
 ## Deferred opening
 By design, the ephemeral resources cannot be opened if the configuration is not fully known.

website/docs/language/meta-arguments/count.mdx

@@ -7,7 +7,7 @@ description: >-
 # The `count` Meta-Argument
 
 :::note
-A given resource or module block cannot use both `count` and `for_each`.
+A given resource or module block cannot use `count` together with `enabled` or `for_each`.
 :::
 
 By default, a [resource block](../../language/resources/syntax.mdx) configures one real
@@ -45,6 +45,13 @@ resource "aws_instance" "server" {
 }
 ```
 
+:::tip
+If you're using `count = var.enabled ? 1 : 0` to conditionally enable/disable a
+single resource or module, consider using the [the `enabled` argument in a `lifecycle` block](../../language/meta-arguments/enabled.mdx)
+argument instead. It provides cleaner syntax without requiring array indexing and supports
+automatic migration from the `count` pattern.
+:::
+
 ## The `count` Object
 
 In blocks where `count` is set, an additional `count` object is

website/docs/language/meta-arguments/enabled.mdx

@@ -0,0 +1,81 @@
+---
+description: >-
+  The enabled meta-argument allows you to conditionally create or skip a single
+  resource or module instance based on a boolean value.
+---
+
+# The `enabled` Meta-Argument
+
+:::note
+A given resource or module block cannot use `enabled` together with `count` or `for_each`.
+:::
+
+The `enabled` meta-argument in a `lifecycle` block provides a cleaner way to conditionally create or skip a
+single resource or module instance. Unlike the traditional `count = var.enabled ? 1 : 0`
+workaround, which requires array indexing to access single instances, `enabled` allows
+direct access when the resource is created and properly handles the null state when disabled.
+
+## Basic Syntax
+
+`enabled` is a meta-argument that goes inside a `lifecycle` block. It accepts expressions that turn into boolean values to determine whether the resource or module should be created.
+
+```hcl
+variable "create_instance" {
+  type    = bool
+  default = true
+}
+
+resource "aws_instance" "example" {
+  # ...
+  lifecycle {
+    enabled = var.create_instance
+  }
+}
+```
+
+When `enabled` is `true` (or not specified), the resource behaves normally. When `enabled`
+is `false`, the resource is not created and evaluates to `null`.
+
+## Accessing Disabled Resources
+
+When a resource might be disabled, it evaluates to `null` and cannot be accessed directly.
+You must use conditional expressions to handle this safely:
+
+```hcl
+# Using try() - most concise but masks other errors
+output "instance_id" {
+  value = try(aws_instance.example.id, "not-created")
+}
+
+# Using null check - most verbose but clearest intent
+output "instance_id" {
+  value = aws_instance.example != null ? aws_instance.example.id : "not-created"
+}
+```
+
+Attempting to directly access a resource configured with `enabled = false` will result in an error during `plan` or `apply`:
+
+```
+│ Error: Attempt to get attribute from null value
+│
+│   on main.tf line 10, in output "instance_id":
+│   10:     value = aws_instance.example.id
+│     ├────────────────
+│     │ aws_instance.example is null
+│
+│ This value is null, so it does not have any attributes.
+```
+
+## Restrictions
+
+The `enabled` meta-argument cannot be used together with [`count`](../../language/meta-arguments/count.mdx) or [`for_each`](../../language/meta-arguments/for_each.mdx), as these
+meta-arguments serve different purposes. Use `enabled` for conditionally creating
+single-instance resources, [`count`](../../language/meta-arguments/count.mdx) for creating multiple numbered instances, or
+[`for_each`](../../language/meta-arguments/for_each.mdx) for creating multiple named instances.
+
+The `enabled` meta-argument cannot use:
+- Unknown values (values not known until apply)
+- Sensitive values
+- Null values
+- Ephemeral values
+- Non-boolean values

website/docs/language/meta-arguments/for_each.mdx

@@ -20,7 +20,7 @@ a set of strings, OpenTofu creates one instance for each member of
 that map or set.
 
 :::note
-A given resource or module block cannot use both `count` and `for_each`.
+A given resource or module block cannot use `for_each` together with `count` or `enabled`.
 :::
 
 ## Basic Syntax

website/docs/language/meta-arguments/lifecycle.mdx

@@ -26,8 +26,15 @@ resource "azurerm_resource_group" "example" {
 The `lifecycle` block and its contents are meta-arguments, available
 for all `resource` blocks regardless of type.
 
-The arguments available within a `lifecycle` block are `create_before_destroy`,
-`prevent_destroy`, `ignore_changes`, and `replace_triggered_by`.
+The arguments available within a `lifecycle` block are `enabled`,
+`create_before_destroy`, `prevent_destroy`, `ignore_changes`, and `replace_triggered_by`.
+
+* `enabled` (bool) - Controls whether a resource is created and managed by OpenTofu.
+  When set to `false`, the resource is excluded from the configuration as if it didn't exist,
+  and any existing infrastructure object will be destroyed. When set to `true` (the default),
+  the resource operates normally.
+
+  For full details about the `enabled` meta-argument, see [its documentation](../../language/meta-arguments/enabled.mdx).
 
 * `create_before_destroy` (bool) - By default, when OpenTofu must change
   a resource argument that cannot be updated in-place due to

website/docs/language/modules/syntax.mdx

@@ -130,7 +130,32 @@ described in more detail in the following pages:
   [the `depends_on` page](../../language/meta-arguments/depends_on.mdx)
   for details.
 
-OpenTofu does not use the `lifecycle` argument. However, the `lifecycle` block is reserved for future versions.
+- `lifecycle` - Allows lifecycle customizations for modules. Currently only
+  supports the `enabled` argument.
+
+## Module Lifecycle
+
+The `lifecycle` block can be used within a `module` block to customize module behavior.
+Currently, it only supports the `enabled` argument for conditionally enabling or disabling
+entire modules:
+
+```hcl
+variable "enable_monitoring" {
+  type    = bool
+  default = true
+}
+
+module "monitoring" {
+  source = "./monitoring"
+
+  lifecycle {
+    enabled = var.enable_monitoring
+  }
+}
+```
+
+For complete details about the `enabled` argument, including restrictions and migration
+from the `count` workaround, see the [`lifecycle` meta-argument documentation](../../language/meta-arguments/lifecycle.mdx).
 
 ## Accessing Module Output Values
 
@@ -210,4 +235,4 @@ removed {
 ```
 :::note
 In contrast with `resource` blocks removal, `removed` blocks pointing to modules, do not allow usage of `provisioners`.
-:::
+:::

website/docs/language/resources/syntax.mdx

@@ -181,6 +181,7 @@ The `provisioner` block will be executed only when the `removed` block is config
 In any other cases, the execution will be skipped.
 
 For more information about provisioners, you can refer to this [page](./provisioners/syntax.mdx).
+
 ## Meta-Arguments
 
 The OpenTofu language defines several meta-arguments, which can be used with
@@ -189,6 +190,7 @@ any resource type to change the behavior of resources.
 The following meta-arguments are documented on separate pages:
 
 - [`depends_on`, for specifying hidden dependencies](../../language/meta-arguments/depends_on.mdx)
+- [`enabled`, for creating conditionally single-resource instances according to a expression](../../language/meta-arguments/enabled.mdx)
 - [`count`, for creating multiple resource instances according to a count](../../language/meta-arguments/count.mdx)
 - [`for_each`, to create multiple instances according to a map, or set of strings](../../language/meta-arguments/for_each.mdx)
 - [`provider`, for selecting a non-default provider configuration](../../language/meta-arguments/resource-provider.mdx)