Validating the template

Whenever we execute aws cloudformation create-stack (or update-stack), CloudFormation will first validate the template, checking whether it is a valid JSON or YAML file (a syntax check) and whether there are any critical issues, such as circular dependencies.

Although template validation is a necessary step before stack deployment, many things will break stack deployment, even if validation succeeds:

• Missing required resource properties
• Syntax errors and typos in resource property names
• Non-existent resource property values

We could continue with this list, but let’s move from theory to practice.

The command that runs template validation is straightforward:

$ aws cloudformation validate-template --template-body file://path_to_your_template

For example, if we want to validate our core template, we need to run the following command:

$ aws cloudformation validate-template --template-body file://core.yaml

If there is...