Template sections
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 AWS 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 AWS Serverless Application Model (AWS SAM)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.
