How to start %index% with 1 in OS::Heat::ResourceGroup

Question

I use %index% in OS::Heat::ResourceGroup and it starts with a 0 value. I want it to start with the value of 1. How to do it?

resources:
  server_group:
     type: OS::Heat::ResourceGroup
     properties:
        count: 3
        resource_def:
           type: OS::Nova::Server
           name: { get_param: [ server_names, '%index%' ] }

I tried with '%index% + 1' but it did not work:

Error return: invalid literal for int() with base 10: '0 + 1'

Answer 1

You can achieve this using yaql and a template composition. Here is the proof of concept:

First create a template for the resource you wish to create, I called it index.yaml:

heat_template_version: rocky
parameters:
  input:
    type: number
resources:
  incrementor:
    type: OS::Heat::Value
    properties:
      value:
        yaql:
          expression: 1 + int($.data.i)
          data:
            i: {get_param: input}
outputs:
  index:
    value: {get_attr: [incrementor, value]}

In your concrete case, you would have your OS::Nova::Server in here.

Use this template from your main template (I called it group.yaml), creating the group with the incremented index:

heat_template_version: rocky
resources:
  example:
    type: OS::Heat::ResourceGroup
    properties:
      count: 10
      resource_def:
        type: index.yaml
        properties:
          input: "%index%"
outputs:
  incremented_indicies:
    value: {get_attr: [example, index]}

Create the stack from this:

openstack stack create index -t group.yaml

And you will see the list of values, starting at 1 rather than 0:

openstack stack output show index --all   
+----------------------+-------------------------------------------+
| Field                | Value                                     |
+----------------------+-------------------------------------------+
| incremented_indicies | {                                         |
|                      |   "output_key": "incremented_indicies",   |
|                      |   "description": "No description given",  |
|                      |   "output_value": [                       |
|                      |     1,                                    |
|                      |     2,                                    |
|                      |     3,                                    |
|                      |     4,                                    |
|                      |     5,                                    |
|                      |     6,                                    |
|                      |     7,                                    |
|                      |     8,                                    |
|                      |     9,                                    |
|                      |     10                                    |
|                      |   ]                                       |
|                      | }                                         |
+----------------------+-------------------------------------------+

---

Why the template composition, you ask? Initially, I expected this to work like this:

heat_template_version: rocky

resources:
  example:
    type: OS::Heat::ResourceGroup
    properties:
      count: 10
      resource_def:
        type: OS::Heat::Value
        properties:
          value:
            yaql:
              expression: 1 + int($.data.i)
              data:
                i: "%index%"
outputs:
  sizes:
    value: {get_attr: [example, value]}

It does not, however, as the yaql appears to be evaluated before the index value is filled:

ERROR: Property error: : resources.example.properties.resource_def: : invalid literal for int() with base 10: '%index%'

So the template composition is a workaround.