You can chuck any "low level" code that calls AWS SDK into this gem that might be useful in more than one gem/module.

This command-line util is a wrapper over the cfndsl API.

Given a cfndsl definition, it will create the stack if it does not exist, or call UpdateStack if the stack already does exist i.e. "converge".

Additionally, this util has an option to force a failure if a call to UpdateStack would cause any changes to resources marked as "immutable".

The way this feature works is to use the AWS API to create a "change set" is called before calling UpdateStack.

If any resources are returned in the changeset and that resource has a tag immutable=true then the convergence will fail. Currently, the resource is parsed right out of the JSON of the Clouformation template to see if it is tagged.

Usage:

 cfndsl_converge --path-to-stack resource_cfndsl.rb \
                 --stack-name stack1234 \
                 --path-to-yaml anyparameters.yml \
                 --fail-on-changes-to-immutable-resource true    

• The path-to-yaml is optional (if there are no open bindings in the cfndsl)
• the default value for fail-on-changes-to-immutable-resource is false to maintain backward compatiblity

This command-line util can be mildly useful in writing bash scripts where values stored in YAML need to be consulted by logic in the bash script. With the YAML input/output to cfndsl, this can come in handy as long as you don't need to do anything elaborate with the YAML - i.e. it only reads the keys off the "top-level".

Usage:

 yaml_get <path to YAML file> <key>