Template sections

CloudFormation templates are divided into different sections, and each section is designed to hold a specific type of information. Some sections must be declared in a specific order, and for others, the order doesn't matter. However, as you build your template, it can be helpful to use the logical order shown in the following list because values in one section might refer to values from a previous section.

Important

When authoring templates, do not use duplicate major sections, such as the Resources section. Although CloudFormation might accept the template, it will have an undefined behavior when processing the template, and might incorrectly provision resources, or return inexplicable errors.

Format Version (optional)

The CloudFormation template version that the template conforms to.

Description (optional)

A text string that describes the template. This section must always follow the template format version section.

Metadata (optional)

Objects that provide additional information about the template.

Parameters (optional)

Values to pass to your template at runtime (when you create or update a stack). You can refer to parameters from the Resources and Outputs sections of the template.

Rules (optional)

Validates a parameter or a combination of parameters passed to a template during a stack creation or stack update.

Mappings (optional)

A mapping of keys and associated values that you can use to specify conditional parameter values, similar to a lookup table. You can match a key to a corresponding value by using the Fn::FindInMap intrinsic function in the Resources and Outputs sections.

Conditions (optional)

Conditions that control whether certain resources are created or whether certain resource properties are assigned a value during stack creation or update. For example, you could conditionally create a resource that depends on whether the stack is for a production or test environment.

Transform (optional)

Specifies one or more macros that should be applied during the processing of the template. For serverless applications (also referred to as Lambda applications), specifies the version of the AWS Serverless Application Model (AWS SAM) to use. When you specify a transform, you can use AWS 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 work with template snippets that are stored separately from the main CloudFormation template. You can store your snippet files in an Amazon S3 bucket and then reuse the functions across multiple templates.

Resources (required)

Specifies the stack resources and their properties, such as an Amazon EC2 instance or an Amazon S3 bucket. You can refer to resources in the Resources and Outputs sections of the template.

Outputs (optional)

Describes the values that are returned whenever you view your stack's properties. For example, you can declare an output for an S3 bucket name and then call the describe-stacks AWS CLI command to view the name.