github.com/iaas-resource-provision/iaas-rpc@v1.0.7-0.20211021023331-ed21f798c408/website/docs/language/meta-arguments/lifecycle.html.md (about)

     1  ---
     2  layout: "language"
     3  page_title: "The lifecycle Meta-Argument - Configuration Language"
     4  description: "The meta-arguments in a lifecycle block allow you to customize resource behavior."
     5  ---
     6  
     7  # The `lifecycle` Meta-Argument
     8  
     9  The general lifecycle for resources is described in the
    10  [Resource Behavior](/docs/language/resources/behavior.html) page. Some details of
    11  that behavior can be customized using the special nested `lifecycle` block
    12  within a resource block body:
    13  
    14  ```hcl
    15  resource "azurerm_resource_group" "example" {
    16    # ...
    17  
    18    lifecycle {
    19      create_before_destroy = true
    20    }
    21  }
    22  ```
    23  
    24  ## Syntax and Arguments
    25  
    26  `lifecycle` is a nested block that can appear within a resource block.
    27  The `lifecycle` block and its contents are meta-arguments, available
    28  for all `resource` blocks regardless of type.
    29  
    30  The following arguments can be used within a `lifecycle` block:
    31  
    32  * `create_before_destroy` (bool) - By default, when Terraform must change
    33    a resource argument that cannot be updated in-place due to
    34    remote API limitations, Terraform will instead destroy the existing object
    35    and then create a new replacement object with the new configured arguments.
    36  
    37      The `create_before_destroy` meta-argument changes this behavior so that
    38      the new replacement object is created _first,_ and the prior object
    39      is destroyed after the replacement is created.
    40  
    41      This is an opt-in behavior because many remote object types have unique
    42      name requirements or other constraints that must be accommodated for
    43      both a new and an old object to exist concurrently. Some resource types
    44      offer special options to append a random suffix onto each object name to
    45      avoid collisions, for example. Terraform CLI cannot automatically activate
    46      such features, so you must understand the constraints for each resource
    47      type before using `create_before_destroy` with it.
    48  
    49  * `prevent_destroy` (bool) - This meta-argument, when set to `true`, will
    50    cause Terraform to reject with an error any plan that would destroy the
    51    infrastructure object associated with the resource, as long as the argument
    52    remains present in the configuration.
    53  
    54      This can be used as a measure of safety against the accidental replacement
    55      of objects that may be costly to reproduce, such as database instances.
    56      However, it will make certain configuration changes impossible to apply,
    57      and will prevent the use of the `iaas-rpc.destroy` command once such
    58      objects are created, and so this option should be used sparingly.
    59  
    60      Since this argument must be present in configuration for the protection to
    61      apply, note that this setting does not prevent the remote object from
    62      being destroyed if the `resource` block were removed from configuration
    63      entirely: in that case, the `prevent_destroy` setting is removed along
    64      with it, and so Terraform will allow the destroy operation to succeed.
    65  
    66  * `ignore_changes` (list of attribute names) - By default, Terraform detects
    67    any difference in the current settings of a real infrastructure object
    68    and plans to update the remote object to match configuration.
    69  
    70      The `ignore_changes` feature is intended to be used when a resource is
    71      created with references to data that may change in the future, but should
    72      not affect said resource after its creation. In some rare cases, settings
    73      of a remote object are modified by processes outside of Terraform, which
    74      Terraform would then attempt to "fix" on the next run. In order to make
    75      Terraform share management responsibilities of a single object with a
    76      separate process, the `ignore_changes` meta-argument specifies resource
    77      attributes that Terraform should ignore when planning updates to the
    78      associated remote object.
    79  
    80      The arguments corresponding to the given attribute names are considered
    81      when planning a _create_ operation, but are ignored when planning an
    82      _update_. The arguments are the relative address of the attributes in the
    83      resource. Map and list elements can be referenced using index notation,
    84      like `tags["Name"]` and `list[0]` respectively.
    85  
    86      ```hcl
    87      resource "aws_instance" "example" {
    88        # ...
    89  
    90        lifecycle {
    91          ignore_changes = [
    92            # Ignore changes to tags, e.g. because a management agent
    93            # updates these based on some ruleset managed elsewhere.
    94            tags,
    95          ]
    96        }
    97      }
    98      ```
    99  
   100      Instead of a list, the special keyword `all` may be used to instruct
   101      Terraform to ignore _all_ attributes, which means that Terraform can
   102      create and destroy the remote object but will never propose updates to it.
   103  
   104      Only attributes defined by the resource type can be ignored.
   105      `ignore_changes` cannot be applied to itself or to any other meta-arguments.
   106  
   107  ## Literal Values Only
   108  
   109  The `lifecycle` settings all affect how Terraform constructs and traverses
   110  the dependency graph. As a result, only literal values can be used because
   111  the processing happens too early for arbitrary expression evaluation.