github.com/bengesoff/terraform@v0.3.1-0.20141018223233-b25a53629922/website/source/docs/modules/create.html.markdown (about)

     1  ---
     2  layout: "docs"
     3  page_title: "Creating Modules"
     4  sidebar_current: "docs-modules-create"
     5  ---
     6  
     7  # Creating Modules
     8  
     9  Creating modules in Terraform is easy. You may want to do this to better
    10  organize your code, to make a reusable component, or just to learn more about
    11  Terraform. For any reason, if you already know the basics of Terraform,
    12  creating a module is a piece of cake.
    13  
    14  Modules in Terraform are just folders with Terraform files. In fact,
    15  when you run `terraform apply`, the current working directory holding
    16  the Terraform files you're applying comprise what is called the
    17  _root module_. It itself is a valid module.
    18  
    19  Therefore, you can enter the source of any module, run `terraform apply`,
    20  and expect it to work (assuming you satisfy the required variables, if any).
    21  
    22  ## An Example
    23  
    24  Within a folder containing Terraform configurations, create a subfolder
    25  "child". In this subfolder, make one empty "main.tf" file. Then, back in
    26  the root folder containing the "child" folder, add this to one of the
    27  Terraform files:
    28  
    29  ```
    30  module "child" {
    31  	source = "./child"
    32  }
    33  ```
    34  
    35  This will work. You've created your first module! You can add resources
    36  to the child module to see how that interaction works.
    37  
    38  ## Inputs/Outputs
    39  
    40  To make modules more useful than simple isolated containers of Terraform
    41  configurations, modules can be configured and also have outputs that can be
    42  consumed by the configuration using the module.
    43  
    44  Inputs of a module are [variables](/docs/configuration/variables.html)
    45  and outputs are [outputs](/docs/configuration/outputs.html). There is no
    46  special syntax to define these, they're defined just like any other
    47  variables or outputs.
    48  
    49  In the "child" module we created above, add the following:
    50  
    51  ```
    52  variable "memory" {}
    53  
    54  output "received" {
    55  	value = "${var.memory}"
    56  }
    57  ```
    58  
    59  This will create a required variable "memory" and then an output "received"
    60  that will simply be the value of the memory variable.
    61  
    62  You can then configure the module and use the output like so:
    63  
    64  ```
    65  module "child" {
    66  	source = "./child"
    67  
    68  	memory = "1G"
    69  }
    70  
    71  output "child_memory" {
    72  	value = "${module.child.received}"
    73  }
    74  ```
    75  
    76  If you run `apply`, you'll again see that this works.
    77  
    78  And that is all there is to it. Variables and outputs are used to configure
    79  modules and provide results. Resources within a module are isolated,
    80  and the whole thing is managed as a single unit.
    81  
    82  ## Paths and Embedded Files
    83  
    84  It is sometimes useful to embed files within the module that aren't
    85  Terraform configuration files, such as a script to provision a resource
    86  or a file to upload.
    87  
    88  In these cases, you can't use a relative path, since paths in Terraform
    89  are generally relative to the working directory that Terraform was executed
    90  from. Instead, you want to use a module-relative path. To do this, use
    91  the [path interpolated variables](/docs/configuration/interpolation.html).
    92  
    93  An example is shown below:
    94  
    95  ```
    96  resource "aws_instance" "server" {
    97  	...
    98  
    99  	provisioner "remote-exec" {
   100  		script = "${path.module}/script.sh"
   101  	}
   102  }
   103  ```
   104  
   105  In the above, we use `${path.module}` to get a module-relative path. This
   106  is usually what you'll want in any case.
   107  
   108  ## Nested Modules
   109  
   110  You can use a module within a module just like you would anywhere else.
   111  This module will be hidden from the root user, so you'll have re-expose any
   112  variables if you need to, as well as outputs.
   113  
   114  The [get command](/docs/commands/get.html) will automatically get all
   115  nested modules as well.
   116  
   117  You don't have to worry about conflicting versions of modules, since
   118  Terraform builds isolated subtrees of all dependencies. For example,
   119  one module might use version 1.0 of module "foo" and another module
   120  might use version 2.0 of module "foo", and this would all work fine
   121  within Terraform since the modules are created separately.