Comment 0 for bug 1420196

Nested stacks currently (Heat Template Version 2014-10-16) support the following data types for nested stacks' parameters (or generally stack parameters for that matter):

  string, number, boolean, comma_delimited_list, json

The latter two look like they could theoretically be used for more complex data
structures such as

  * The `networks` attribute of OS::Nova::Server (a list of maps)
  * The `allocation_pools` attribute of OS::Neutron::Subnet (a list of maps)

Hence I tried creating a stack that invoked the attached nested stack as follows:

  network:
    type: networks-wrapper.yaml
    properties:
      cidr: 10.10.10.0/24
      allocation_pools:
        - {start: 10.10.10.10, end: 10.10.10.150}
      name:
        list_join:
          - '_'
          - [ heat, { get_param: 'OS::stack_name' } ]

This resulted in a CREATE_FAILED status with the following stack_status_reason:

| stack_status_reason | Resource CREATE failed: StackValidationFailed: Property |
| | error : subnet: allocation_pools Property error : |
| | allocation_pools: 0 ".member.0.start=10.10.10.10" is |
| | not a map |

Note, that it seems to have passed template validation (if the parameter type
for the allocation_pools parameter in networks-wrapper.yaml is `json`, for
instance, validation simply fails). Apparently the data structure was not
recognized as such. Instead, some kind of serialized representation was passed
to OS::Neutron::Subnet which tripped it up.

Another observation: The problem seems to lie with parameters actually passed
to the template. If the parameter is not being passed, causing the default
value for allocation_pools in networks-wrapper.yaml to be used, the stack will
be created without any problems.