RE: [tosca] RE: updated operational model

[Chris Lauwers <lauwers@ubicity.com>]

Hi Tal, a belated response to one of your earlier emails:

  TOSCA workflows, interfaces, operations, and notifications are only relevant in the context of âpure TOSCA orchestrationâ.

I'm not sure why you would say that.

 

In my opinion, the TOSCA spec is pretty clear about this. From Section 1.3: â Both node and relationship types may define lifecycle operations to implement the behavior an orchestration engine can invoke when instantiating a service templateâ as well as âAn orchestration engine processing a TOSCA service template uses the mentioned lifecycle operations to instantiate single components at runtime, and it uses the relationship between components to derive the order of component instantiationâ.  From Section  5.8: â Interfaces are reusable entities that define a set of operations that that can be included as part of a Node type or Relationship Type definition. Each named operations may have code or scripts associated with them that orchestrators can execute for when transitioning an application to a given stateâ. These statements make it clear that operations are intended to be executed by an Orchestrator, which implies (in my opinion) that if youâre not building a TOSCA Orchestrator, these concepts shouldnât be of concern.

 

Many orchestrators and platforms have equivalents of these, which could be expressed in TOSCA. Examples from my work:

         Turandot, which is not a "pure TOSCA orchestrator", supports operations of various types on pods (using the K8s control plane) and KubeVirt virtual machines (using ssh)

Perhaps I have the wrong understanding, but my impression was that Turandot delegates all orchestration to Kubernetes. If thatâs the case, which piece of software is it that âinvokesâ the operations defined on TOSCA nodes and relationships?

         Puccini, which is not an orchestrator at all, can export TOSCA 1.3 workflows to BPMN2, to be used by a wide variety of orchestrators

Iâm not clear on how this would work. TOSCA operations typically need input values that are retrieved from nodes and relationships in the topology representation graph(using TOSCA intrinsic functions). How do BPMN workflows access this information?

Iâm not trying to be difficult here. These are sincere questions. I would love to understand how you envision this working.

Thanks,

Chris