Comment 7 for bug 1906779

As described in the Bug report, this is not an operation error, but a code issue.

Assuming that one aspectId can scale multiple VDUs according to SOL-VNFD, I think Tacker should be able to:
1) Perform a scale out operation with aspectId as `database`
2) vdu_1 and vdu_2 scale out simultaneously with 1) trigger.
   * vdu_1: two instances are increased.
     ```
     - vdu_1_scaling_aspect_deltas:
         type: tosca.policies.nfv.VduScalingDeltas
         properties:
         aspect: database
         deltas:
           delta_1:
             number_of_instances: 2
         targets: [ vdu_1 ]
     ```
   * vdu_2: three instances are increased.
     ```
     - vdu_2_scaling_aspect_deltas:
         type: tosca.policies.nfv.VduScalingDeltas
         properties:
         aspect: database
         deltas:
           delta_1:
             number_of_instances: 3
         targets: [ vdu_2 ]
     ```

However, with the current implementation of Tacker, neither Openstack VIM nor Kubernetes VIM can scale multiple VDUs at the same time, as described above.

I don't think it's a big problem because operator can define it with different aspectId and scale it with each.
However, if it fully complies with SOL, it may be a necessary modification.
I don't know the details, but I think a big modification is necessary.