# CloudFormation template sections
<a name="template-anatomy"></a>

Every CloudFormation template consists of one or more sections, each serving a specific purpose. 

The **Resources** section is required in every CloudFormation template and forms the core of the template. This section specifies the stack resources and their properties, such as an Amazon EC2 instance or an Amazon S3 bucket. Each resource is defined with a unique logical ID, type, and specific configuration details. 

The **Parameters** section, while optional, plays an important role in making templates more flexible. It allows users to pass values at runtime when creating or updating a stack. These parameters can be referenced in the `Resources` and `Outputs` sections, enabling customization without altering the template itself. For instance, you might use parameters to specify instance types or environment settings that vary between deployments.

The **Outputs** section, also optional, defines the values that are returned when viewing a stack’s properties. Outputs provide useful information such as resource identifiers or URLs, which can be leveraged for operational purposes or for integration with other stacks. This section helps users retrieve and use important details about the resources created by the template.

Other optional sections include **Mappings**, which function like lookup tables to manage conditional values. With mappings, you define key-value pairs and use them with the `Fn::FindInMap` intrinsic function in the `Resources` and `Outputs` sections. This is useful for scenarios where you need to adjust configurations based on conditions such as Amazon Web Services Region or environment.

**Metadata** and **Rules** sections, though less commonly used, provide additional functionality. `Metadata` can include additional information about the template, while `Rules` validates a parameter or a combination of parameters during stack creation or updates, ensuring they meet specific criteria. The **Conditions** section further enhances flexibility by controlling whether certain resources are created or properties are assigned a value based on conditions like environment type.

Lastly, the **Transform** section is used to apply macros during the processing of the template. For serverless applications (also referred to as Lambda applications), it specifies the version of the [Amazon Serverless Application Model (Amazon SAM)](https://github.com/awslabs/serverless-application-specification) to use. When you specify a transform, you can use Amazon SAM syntax to declare resources in your template. The model defines the syntax that you can use and how it's processed. You can also use the `AWS::Include` transform to include template snippets that are stored separately from the main CloudFormation template. 

The following topics provide more information and examples for using each section.

**Topics**
+ [Resources](resources-section-structure.md)
+ [Parameters](parameters-section-structure.md)
+ [Outputs](outputs-section-structure.md)
+ [Mappings](mappings-section-structure.md)
+ [Metadata](metadata-section-structure.md)
+ [Rules](rules-section-structure.md)
+ [Conditions](conditions-section-structure.md)
+ [Transform](transform-section-structure.md)
+ [Format version](format-version-structure.md)
+ [Description](template-description-structure.md)