RandomString validation failure in provider template

[Tomas Sedovic]

Passing OS::Heat::RandomString as a property to a provider template fails validation, if the nested parameter has a length constraint.

Running (templates attached to launchpad) `heat stack-create test -f ~/main.yaml` shows this error:

ERROR: Failed to validate: Parameter 'random_string' is invalid: length (0) is out of range (min: 8, max: 10)

If I change `{get_attr: [rs, value]}` to `{get_resource: rs}` (these should be equivalent according to the documentation), the error is similar but with a different length value:

ERROR: Failed to validate: Parameter 'random_string' is invalid: length (2) is out of range (min: 8, max: 10)

This error was introduced with the "Do static template validation for nested stacks" commit: c31c34f8dfd0919bf46a975701c139073115debc.

[Tomas Sedovic (tsedovic)]

This affects the "without-mergepy" templates in TripleO. See the f20 job failure here:

https://review.openstack.org/#/c/140375/

[Steven Hardy (shardy)]

I think this is a duplicate of the following bugs:

https://bugs.launchpad.net/heat/+bug/1407392
https://bugs.launchpad.net/heat/+bug/1407100
https://bugs.launchpad.net/heat/+bug/1407877
https://bugs.launchpad.net/heat/+bug/1401317

I've posted some patches which fix the problem in heat, they're not yet merged:

https://review.openstack.org/#/c/144766/

The problem is we introduced validation which checks the nested template is valid, but we don't want to validate the values at validation (pre-create) time, because indirect references to resources which haven't yet been created may provide invalid values.

A workaround would be to move the RandomString resource inside the nested template, but we should merge the fix to heat soon.