AWS CloudFormation Linter Custom Rules
June 30, 2021 #aws #cloudformation
While diving deep on AWS CloudFormation Linter (cfn-lint), I discovered Custom Rules support.
The linter supports the creation of custom one-line rules which compare any resource with a property using pre-defined operators.
To give it a try, I created a simple rule that enforced a naming standard for my Python Lambda functions by creating
cfn_custom_rules.txt containing my custom rule.
AWS::Lambda::Function Handler EQUALS "app.lambda_handler" WARN "Lambda function handler should be app.lambda_handler"
Then when I run
cfn-lint, I can include evaluation of this custom rule file.
$ cfn-lint template.yaml --custom-rules cfn_custom_rules.txt
Of course, I need this in my
buildspec.yml so AWS CodePipeline and AWS CodeBuild would enforce this.
pre_build: commands: - cfn-lint template.yaml --custom-rules cfn_custom_rules.txt - status=$? - | if [ $status -ne 0 ]; then exit 1; fi
An alternative to the
--custom-rules CLI option is to add a section to my
.cfnlintrc.yaml to automatically enable this option and allows for easy integration with the Visual Studio Code vscode-cfn-lint extension.
# https://github.com/aws-cloudformation/cfn-lint#configuration custom_rules: cfn_custom_rules.txt