github.com/rstandt/terraform@v0.12.32-0.20230710220336-b1063613405c/website/docs/configuration-0-11/locals.html.md (about)

     1  ---
     2  layout: "docs"
     3  page_title: "Local Values - 0.11 Configuration Language"
     4  sidebar_current: "docs-conf-old-locals"
     5  description: |-
     6    Local values assign a name to an expression that can then be used multiple times
     7    within a module.
     8  ---
     9  
    10  # Local Values
    11  
    12  -> **Note:** This page is about Terraform 0.11 and earlier. For Terraform 0.12
    13  and later, see
    14  [Configuration Language: Configuring Local Values](../configuration/locals.html).
    15  
    16  Local values assign a name to an expression, that can then be used multiple
    17  times within a module.
    18  
    19  Comparing modules to functions in a traditional programming language,
    20  if [variables](./variables.html) are analogous to function arguments and
    21  [outputs](./outputs.html) are analogous to function return values then
    22  _local values_ are comparable to a function's local variables.
    23  
    24  This page assumes you're already familiar with
    25  [the configuration syntax](./syntax.html).
    26  
    27  ## Examples
    28  
    29  Local values are defined in `locals` blocks:
    30  
    31  ```hcl
    32  # Ids for multiple sets of EC2 instances, merged together
    33  locals {
    34    instance_ids = "${concat(aws_instance.blue.*.id, aws_instance.green.*.id)}"
    35  }
    36  
    37  # A computed default name prefix
    38  locals {
    39    default_name_prefix = "${var.project_name}-web"
    40    name_prefix         = "${var.name_prefix != "" ? var.name_prefix : local.default_name_prefix}"
    41  }
    42  
    43  # Local values can be interpolated elsewhere using the "local." prefix.
    44  resource "aws_s3_bucket" "files" {
    45    bucket = "${local.name_prefix}-files"
    46    # ...
    47  }
    48  ```
    49  
    50  Named local maps can be merged with local maps to implement common or default
    51  values:
    52  
    53  ```hcl
    54  # Define the common tags for all resources
    55  locals {
    56    common_tags = {
    57      Component   = "awesome-app"
    58      Environment = "production"
    59    }
    60  }
    61  
    62  # Create a resource that blends the common tags with instance-specific tags.
    63  resource "aws_instance" "server" {
    64    ami           = "ami-123456"
    65    instance_type = "t2.micro"
    66  
    67    tags = "${merge(
    68      local.common_tags,
    69      map(
    70        "Name", "awesome-app-server",
    71        "Role", "server"
    72      )
    73    )}"
    74  }
    75  ```
    76  
    77  ## Description
    78  
    79  The `locals` block defines one or more local variables within a module.
    80  Each `locals` block can have as many locals as needed, and there can be any
    81  number of `locals` blocks within a module.
    82  
    83  The names given for the items in the `locals` block must be unique throughout
    84  a module. The given value can be any expression that is valid within
    85  the current module.
    86  
    87  The expression of a local value can refer to other locals, but as usual
    88  reference cycles are not allowed. That is, a local cannot refer to itself
    89  or to a variable that refers (directly or indirectly) back to it.
    90  
    91  It's recommended to group together logically-related local values into
    92  a single block, particularly if they depend on each other. This will help
    93  the reader understand the relationships between variables. Conversely,
    94  prefer to define _unrelated_ local values in _separate_ blocks, and consider
    95  annotating each block with a comment describing any context common to all
    96  of the enclosed locals.