Custom names for resources in cluster created using HEAT templates in Openstack

I am trying to create a cluster using Heat Templates of Openstack. I have following template defining my resource group.

cluster:
    type: OS::Heat::ResourceGroup
    properties:
        count: { get_param: instance_count }
        resource_def:
            type: ../templates/vm.yaml
            properties:
                image: { get_param: image }
                flavor: { get_param: flavor }
                private_network : { get_attr : [network, name] }

This works, but the name of all these servers is very cryptic. I was wondering if it would be possible to provide a prefix to name to each of the instances.

Or another way could be is I can str_replace a template value with the current index of the cluster count.

Is there a way to achieve this?

Nevermind, got it from the ResourceGroup documentation. Use %index%.

Here is the example from the documentation.

resources:
  my_indexed_group:
    type: OS::Heat::ResourceGroup
    properties:
      count: 3
      resource_def:
        type: OS::Nova::Server
        properties:
          # create a unique name for each server
          # using its index in the group
          name: my_server_%index%
          image: CentOS 6.5
          flavor: 4GB Performance