The Scale Workflow

Workflow name: ``scale``

Workflow description:

Scales out/in the node subgraph of the system topology applying the install/uninstall workflows’ logic respectively.

If the entity denoted by scalable_entity_name is a node template that is contained in a compute node (or is a compute node itself) and scale_compute is true, the node graph will consist of all nodes that are contained in the compute node which contains scalable_entity_name and the compute node itself. Otherwise, the subgraph will consist of all nodes that are contained in the node/scaling group denoted by scalable_entity_name.

In addition, nodes that are connected to nodes that are part of the contained subgraph will have their establish relationship operations executed during scale out and their unlink relationship operations executed during scale in.

Workflow parameters:

  • ``scalable_entity_name``: The name of the node/scaling group to apply the scaling logic to.
  • ``delta``: The scale factor. (Default: 1)
    • For delta > 0: If the current number of instances is N, scale out to N + delta.
    • For delta < 0: If the current number of instances is N, scale in to N - |delta|.
    • For delta == 0, leave things as they are.
  • scale_compute: should scale apply on the compute node containing the node denoted by scalable_entity_name (default value is false).
    • If scalable_entity_name specifies a node, and scale_compute is set to false, the subgraph will consist of all the nodes that are contained in the that node and the node itself.
    • If scalable_entity_name specifies a node, and scale_compute is set to true, the subgraph will consist of all nodes that are contained in the compute node that contains the node denoted by scalable_entity_name and the compute node itself.
    • If the node denoted by scalable_entity_name is not contained in a compute node or it specifies a group name, this parameter is ignored.

Workflow high-level pseudo-code:

  1. Retrieve the scaled node/scaling group, based on scalable_entity_name and scale_compute parameters.
  2. Start deployment modification, adding or removing node instances and relationship instances.
  3. If delta > 0:
    • Execute install lifecycle operations (create, configure, start) on added node instances.
    • Execute the establish relationship lifecycle operation for all affected relationships.
  4. If delta < 0:
    • Execute the unlink relationship lifecycle operation for all affected relationships.
    • Execute uninstall lifecycle operations (stop, delete) on removed node instances.

NOTE: Detailed description of the terms graph and sub-graph that are used in this section, can be found in the Heal workflow section.

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