aws-cloudformation
A way to validate min length for List types
Name of the resource
Other
Resource name
ListAWS::EC2::AvailabilityZone::Name
Description
Hey All, I've looked everywhere in the documentation and examples in GitHub, but somehow I don't see this kind of validation anywhere. There are some use cases in which we want a user to choose a list of subnets with a min size of 2 for example, I can't see a way to validate that. Not with rules (which is less ideal) and not with a dedicated property.
It is possible to validate that the List<Resource> is not empty (with AllowedPattern) but not a min size of the list.
So the request is to add MinLength / MinSize to the List types (e.g. ListAWS::EC2::AvailabilityZone::Name). If someone got a workaround for the time being it would be greatly appreciated.
P.S. MinLength somehow works to validate non-empty lists but does not validate length for Lists.
Other Details
No response
@chkp-dmitrytc Thank you very much for your feedback! Since this repository is focused on resource coverage, I'm transferring this issue over to a new GitHub repository dedicated to CloudFormation template language issues.
I haven't tested this, but have you tried using an AllowedPattern?
AllowedPattern: '.*,.*'
I believe I did, and I've also tried to play with length-dependent regex, without success.
I tried:
AllowedPattern: '.{27,}' (27 because each item in the list is 26 characters long)
This did not work as well.
I found out that:
AllowedPattern: '.{26}'
Matched when one item was selected and multiple items were selected.
meaning, the system checks one item's pattern, even if multiple are selected.
I don't want to transform this into a regex discussion, but ^.{26}$ should match exact 26 characters.
If you want to make the ,-based regex a bit more robust, you could use:
^([^,]{26},)+[^,]{26}$
Which translates to: From the start of the string (^), have at least one (+) group of 26 characters that are not a comma followed by a comma(([^,]{26},)). Right before the end of the string ($) have another group of 26 non-comma characters ([^,]{26}).
Or shorter: at least 2 times a group of 26 characters
I forgot to write in the comment the ^ and $ but if I recall correctly that's how I've tested it :)
I used the '.{27,}' to test if there was a string longer than 26 characters (27 and above), I purposely did not use , as a character to make it more generic.
So '.{27,}' always did not match, no matter how many items were selected. So my conclusion was that the pattern that is examined is of a single item (there was no string greater than 26 characters long no matter the selection).
I see what you're saying, thanks for the clarification. A more hacky workaround is to use a String as parameter type, and use Fn::Split to convert it to a list in the Resources section