github.com/hugorut/terraform@v1.1.3/website/docs/language/modules/develop/index.mdx (about)

     1  ---
     2  page_title: Creating Modules
     3  description: >-
     4    Modules are containers for multiple resources that are used together in a
     5    configuration. Learn when to create modules and about module structure.
     6  ---
     7  
     8  # Creating Modules
     9  
    10  > **Hands-on:** Try the [Reuse Configuration with Modules](https://learn.hashicorp.com/collections/terraform/modules?utm_source=WEBSITE&utm_medium=WEB_IO&utm_offer=ARTICLE_PAGE&utm_content=DOCS) collection on HashiCorp Learn.
    11  
    12  A _module_ is a container for multiple resources that are used together.
    13  Modules can be used to create lightweight abstractions, so that you can
    14  describe your infrastructure in terms of its architecture, rather than
    15  directly in terms of physical objects.
    16  
    17  The `.tf` files in your working directory when you run [`terraform plan`](/cli/commands/plan)
    18  or [`terraform apply`](/cli/commands/apply) together form the _root_
    19  module. That module may [call other modules](/language/modules/syntax#calling-a-child-module)
    20  and connect them together by passing output values from one to input values
    21  of another.
    22  
    23  To learn how to _use_ modules, see [the Modules configuration section](/language/modules).
    24  This section is about _creating_ re-usable modules that other configurations
    25  can include using `module` blocks.
    26  
    27  ## Module structure
    28  
    29  Re-usable modules are defined using all of the same
    30  [configuration language](/language) concepts we use in root modules.
    31  Most commonly, modules use:
    32  
    33  * [Input variables](/language/values/variables) to accept values from
    34    the calling module.
    35  * [Output values](/language/values/outputs) to return results to the
    36    calling module, which it can then use to populate arguments elsewhere.
    37  * [Resources](/language/resources) to define one or more
    38    infrastructure objects that the module will manage.
    39  
    40  To define a module, create a new directory for it and place one or more `.tf`
    41  files inside just as you would do for a root module. Terraform can load modules
    42  either from local relative paths or from remote repositories; if a module will
    43  be re-used by lots of configurations you may wish to place it in its own
    44  version control repository.
    45  
    46  Modules can also call other modules using a `module` block, but we recommend
    47  keeping the module tree relatively flat and using [module composition](/language/modules/develop/composition)
    48  as an alternative to a deeply-nested tree of modules, because this makes
    49  the individual modules easier to re-use in different combinations.
    50  
    51  ## When to write a module
    52  
    53  In principle any combination of resources and other constructs can be factored
    54  out into a module, but over-using modules can make your overall Terraform
    55  configuration harder to understand and maintain, so we recommend moderation.
    56  
    57  A good module should raise the level of abstraction by describing a new concept
    58  in your architecture that is constructed from resource types offered by
    59  providers.
    60  
    61  For example, `aws_instance` and `aws_elb` are both resource types belonging to
    62  the AWS provider. You might use a module to represent the higher-level concept
    63  "[HashiCorp Consul](https://www.consul.io/) cluster running in AWS" which
    64  happens to be constructed from these and other AWS provider resources.
    65  
    66  We _do not_ recommend writing modules that are just thin wrappers around single
    67  other resource types. If you have trouble finding a name for your module that
    68  isn't the same as the main resource type inside it, that may be a sign that
    69  your module is not creating any new abstraction and so the module is
    70  adding unnecessary complexity. Just use the resource type directly in the
    71  calling module instead.
    72  
    73  ## Refactoring module resources
    74  
    75  You can include [refactoring blocks](/language/modules/develop/refactoring) to record how resource
    76  names and module structure have changed from previous module versions.
    77  Terraform uses that information during planning to reinterpret existing objects
    78  as if they had been created at the corresponding new addresses, eliminating a
    79  separate workflow step to replace or migrate existing objects.