Using a linter for best practices on templates

Let's describe a linter again. This is how Wikipedia defines a linter:

"Lint, or a linter, is a tool that analyzes source code to flag programming errors, bugs, stylistic errors, and suspicious constructs."

CloudFormation's linter, known as a cfn-lint, is a command-line tool that inspects your template and compares the declared resources against a wide range of written rules.

Unlike the template validator, cfn-lint can detect tricky issues such as missing resource properties or arguments in an intrinsic function.

CloudFormation's linter is an external tool that can be installed using pip:

$ pip install cfn-lint

It will automatically appear in $PATH, so we can run it right away:

$ cfn-lint core.yaml

If the template meets all the rule requirements, we will see nothing on the output (and the return code of the command will be 0). However, if there is an error, the linter will notify us immediately...