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Over time the discussion about "lifecycle" blocks in the documentation became confusing because the docs originally written for managed resource lifecycle got partially generalized for resources of other modes and for module calls, even though each of those has a completely different lifecycle and thus a different set of lifecycle settings. This is a first pass at trying to reorganize that so that the "lifecycle" page is really just an index of all of the different kinds of lifecycle block that exist in the language, while the main documentation for each use of that block type now belongs with the documentation of the block it's nested within. While working on this I also found that there was some duplication inside the "data sources" page where the same information was described multiple times, and a few other cases where things had become inconsistent over time. This also includes a little extra content to try to clarify the difference between managed, data, and ephemeral resources and to make it explicit that the "Resources" section is focused only on managed resources because that is the primary resource mode. As usual there's lots more that could be done here -- this documentation has gradually evolved over time and is full of weird quirks due to that evolution -- but I decided to draw a line here so that the diff wouldn't get too large. Signed-off-by: Martin Atkins <mart@degeneration.co.uk>
83 lines
3.0 KiB
Plaintext
83 lines
3.0 KiB
Plaintext
---
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description: >-
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Retrieves the root module output values from an OpenTofu state snapshot stored
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in a remote backend.
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---
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# The `terraform_data` Managed Resource Type
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The `terraform_data` implements the standard resource lifecycle, but does not directly take any other actions.
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You can use the `terraform_data` resource without requiring or configuring a provider. It is always available through a built-in provider with the [source address](../../language/providers/requirements.mdx#source-addresses) `terraform.io/builtin/terraform`.
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The `terraform_data` resource is useful for storing values which need to follow a manage resource lifecycle, and for triggering provisioners when there is no other logical managed resource in which to place them.
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## Example Usage (data for `replace_triggered_by`)
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[The `replace_triggered_by` lifecycle argument](behavior.mdx#replace_triggered_by) requires all of the given addresses to be for resources, because the decision to force replacement is based on the planned actions for all of the mentioned resources.
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Plain data values such as [Local Values](../../language/values/locals.mdx) and [Input Variables](../../language/values/variables.mdx) don't have any side-effects to plan against and so they aren't valid in `replace_triggered_by`. You can use `terraform_data`'s behavior of planning an action each time `input` changes to _indirectly_ use a plain value to trigger replacement.
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```hcl
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variable "revision" {
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default = 1
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}
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resource "terraform_data" "replacement" {
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input = var.revision
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}
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# This resource has no convenient attribute which forces replacement,
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# but can now be replaced by any change to the revision variable value.
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resource "example_database" "test" {
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lifecycle {
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replace_triggered_by = [terraform_data.replacement]
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}
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}
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```
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## Example Usage (`null_resource` replacement)
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```hcl
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resource "aws_instance" "web" {
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# ...
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}
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resource "aws_instance" "database" {
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# ...
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}
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# A use-case for terraform_data is as a do-nothing container
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# for arbitrary actions taken by a provisioner.
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resource "terraform_data" "bootstrap" {
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triggers_replace = [
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aws_instance.web.id,
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aws_instance.database.id
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]
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provisioner "local-exec" {
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command = "bootstrap-hosts.sh"
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}
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}
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```
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`moved` block can be used to migrate from the `null_resource` to the `terraform_data` resource. [Migration guide](https://search.opentofu.org/provider/hashicorp/null/latest/docs/guides/terraform-migration)
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## Argument Reference
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The following arguments are supported:
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* `input` - (Optional) A value which will be stored in the instance state, and reflected in the `output` attribute after apply.
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* `triggers_replace` - (Optional) A value which is stored in the instance state, and will force replacement when the value changes.
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## Attributes Reference
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In addition to the above, the following attributes are exported:
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* `id` - A string value unique to the resource instance.
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* `output` - The computed value derived from the `input` argument. During a plan where `output` is unknown, it will still be of the same type as `input`.
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