# Use modules from the CloudFormation private registry
<a name="modules-using"></a>

This topic explains how to use modules in CloudFormation templates. Think of modules as pre-made bundles of resources that you can add to your templates.

To use a module, the steps are as follows:
+ **Register the module** – You register modules in the CloudFormation registry as private extensions. Make sure it's registered in the AWS account and Region you’re working in. For more information, see [CloudFormation registry concepts](registry-concepts.md).
+ **Include it in your template** – Add the module to the [Resources](resources-section-structure.md) section of your CloudFormation template, just like you would with other resources. You'll also need to provide any required properties for the module.
+ **Create or update the stack** – When you initiate a stack operation, CloudFormation generates a processed template that resolves any included modules into the appropriate resources. 
+ **Preview changes** – Before making changes, you can use a change set to see what resources will be added or changed. For more information, see [Update CloudFormation stacks using change sets](using-cfn-updating-stacks-changesets.md).

Consider the following example: you have a template that contains both resources and modules. The template contains one individual resource, `ResourceA`, as well as a module, `ModuleParent`. That module contains two resources, `ResourceB` and `ResourceC`, as well as a nested module, `ModuleChild`. `ModuleChild` contains a single resource, `ResourceD`. If you create a stack from this template, CloudFormation processes the template and resolves the modules to the appropriate resources. The resulting stack has four resources: `ResourceA`, `ResourceB`, `ResourceC`, and `ResourceD`.

![\[During a stack operation, CloudFormation resolves the two modules included in the stack template into the appropriate four resources.\]](http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/images/modules-resource-inclusion.png)


CloudFormation keeps track of which resources in a stack were created from modules. You can view this information on the **Events**, **Resources**, and **Drifts** tabs for a given stack, and it's also included in change set previews.

Modules are distinguishable from resources in a template because they adhere to the following four-part naming convention, as opposed to the typical three-part convention used by resources:

```
organization::service::use-case::MODULE
```