Comment 6 for bug 1439754

In my template I was using a random string to populate instances metadata:
...
  metadata_common_id:
    type: OS::Heat::RandomString
...
  web_group:
    ...
          database_password: { get_attr: [mysql, database_password] }
          metadata_common_id: {get_resource: metadata_common_id}
          web_security_group: {get_resource: web_security_group}
...
  cpu_alarm_high:
    ...
    matching_metadata: {'metadata.user_metadata.stack': {get_resource: metadata_common_id}

I changed the random string with OS::stack_id value and the autoscaling group began to work properly. Now min_size and max_size are respected.