In my templates, I provide exactly this functionality, but rather than using templating in my templates, I use substitution mapping instead. This aligns philosophically better with intent-based orchestration anyway. At the highest level
of abstraction, a user-provided input will specify if load balancing is required or not (similar to Peter s earlier example where someone would specify if firewalling is required or not). The orchestrator will then substitute either a template that includes
a load balancer, or a template that includes a web frontend.
By the way, this is exactly what ETSI NFV does as well: they provide variability in VNFs by using substitution mapping to deploy different deployment flavors.
Chris
From: Tal Liron <
tliron@redhat.com>
Sent: Friday, January 28, 2022 1:54 PM
To: Bruun, Peter Michael (CMS RnD Orchestration) <
peter-michael.bruun@hpe.com>
Cc: Chris Lauwers <
lauwers@ubicity.com>;
tosca@lists.oasis-open.org Subject: Re: [tosca] Re: Differentiating TOSCA from HEAT
I'll help. When I said "it's already the case" I meant that in reference to Peter's comment directly above (I was responding inline) about the very limited variability that TOSCA offers using topology inputs. I don't think topology inputs
and the get_input function are controversial. They are already here, always have been, and are part of how we understand TOSCA. They are right there in the "mental model" for the TOSCA processor that we all agreed upon.
What would be controversial is to change TOSCA in a way that would allow for topological variability. For example something like this:
topology_template:
node_templates:
{% if inputs.loadbalancing == true %}
frontend:
type: Loadbalancer
{% else %}
frontend:
type: Web
{% endif %}
monitor:
type: Monitor
{% if inputs.loadbalancing == true %}
requirements:
- instance: frontend
{% endif %}
If there are people who want TOSCA to have built-in support for this ... well, I don't think we would all agree to that. I would be very worried about the implications. Are you suggesting that we need to add features for such total variability
in TOSCA? It sounds to me that you're aligned with me and Peter on this. So maybe there's a different misunderstanding here.
Lacking such total variability, users that need it -- and don't want to maintain multiple complete .yaml files with identical portions -- would thus introduce a preprocessor. That's what I mean by "inevitable" -- there's absolutely no way
for us to forbid it. So, I think it's best for us to acknowledge that such usages exist and
perhaps find a way to deal with them in spec (e.g. by supporting them in CSAR).
On Fri, Jan 28, 2022 at 2:09 PM Bruun, Peter Michael (CMS RnD Orchestration) <
peter-michael.bruun@hpe.com > wrote:
Thanks Tal,
I find this answer contradictory.
Either TOSCA has the expressive power required for the intended variability or it doesn t.
You say that pre-processing is
inevitable because it isn t, but you also say it
is already the case , because it is. I am unable to reconcile those statements, please help.
From the inevitable part, I think you mean isn t , and so clearly, in your opinion TOSCA
is not and should not be ( undesirable ) sufficiently expressive for day 0 because if it were, then there would be no need for pre-processors.
If there can be a pre-processor input format that is more expressive than TOSCA, and you do say if not support it, in our specs ,
then yes our specs should be standardizing that format as TOSCA . Unfortunately, this would introduce yet one or two layers of parameterization on top of those of YAML, inputs, properties and attributes, and it would further complicate the language.
Alternatively, the role of TOSCA becomes
just as an intermediate format, useful for checking consistency of the output from whatever tool produced TOSCA.
I am not sure how to progress from here
Peter
From:
tosca@lists.oasis-open.org [mailto:
tosca@lists.oasis-open.org ]
On Behalf Of Tal Liron
Sent: 28. januar 2022 18:07
To: Bruun, Peter Michael (CMS RnD Orchestration) <
peter-michael.bruun@hpe.com >
Cc: Chris Lauwers <
lauwers@ubicity.com >;
tosca@lists.oasis-open.org Subject: [tosca] Re: Differentiating TOSCA from HEAT
On Fri, Jan 28, 2022 at 5:32 AM Bruun, Peter Michael (CMS RnD Orchestration) <
peter-michael.bruun@hpe.com > wrote:
All potential
intended variability of each type of service in the catalog must be easily expressible as a function of the inputs. Note that this creates two levels of intent based , and I am not sure that was clear in the previous work on TOSCA for intent based modeling:
The intent of the Day 0 designer to express in as few templates as possible the intended variability offered to the Day 1+ users
The intent of the Day 1+ users, expressed by a) selecting a template from the catalog and b) providing input values
I think there's great no need to say so, because this is already the case. :) But it won't hurt to make it clear.
If the expressive power of inputs is too low (or too hard to use), then the users will begin to spawn variants of the templates for those cases that
are not expressible. I hope we all agree that that is undesirable.
Alternatively, we face another bad scenario, that to express the intended variability, users invent their own home-grown formats to use as input to some
TOSCA-generating scripts. That road, in my opinion defies the purpose of TOSCA as a standard.
I think this is inevitable, but I also don't think it's the end of the world.
There are two ways to approach variability:
1) Integrate variability into TOSCA. This, I think is undesirable. Take a look at Helm charts -- what an unholy mess. Not only can they not be validated at design time, they are
almost impossible to read, modify, or fix. They even allow for (code) plugins that do custom variability. This should be the poster child for the opposite of what TOSCA purports to be.
2) Add a preprocessor to the toolchain. You called it a "TOSCA-generating script" but it also can be some kind of template modification (not full generation). I'm not a fan of text
templating for YAML, but otherwise it is possible to create some other higher-level templating that is purpose-built for YAML, and perhaps even purpose-built for TOSCA. (This is an idea for a project if someone wants to contribute to the ecosystem!)
The idea of TOSCA being part of a toolchain is central to how I think about it. Because I deal with already-existing orchestrators such as Ansible and Terraform or larger pyramids
of orchestrator, I must think of TOSCA as being an input (albeit a processed input, and even a continuous input for Day 2 when I deal with attributes) into the next step in the process. I am not going to, and cannot, fork my orchestration universe in order
to redesign it around a specific version of TOSCA.
And so I don't find it particularly offensive to have something before TOSCA in the toolchain. Another reason for this is that I have a lot of trust in TOSCA's validation capability.
If the pre-processor creates a broken design then the TOSCA processor will emit an error and we won't continue in the toolchain. (Yet another reason for my adamant resistance to allow for requirements to "dangle".)
Actually, I had some thoughts about enhancing the CSAR format to specifically allow for pre-processors. Basically some kind of META directive that instructs the toolchain to do
something else first before using the ".tosca" files therein. This would allow TOSCA inventory systems (such as used by ONAP) to continue using CSAR, at least, in a standard way. (A preprocessor for an entire CSAR would be quite painful.)
And by the way preprocessing isn't just for variability of topologies, but also for profiles. I'm thinking of something simple like specifying the profile version somewhere outside
of TOSCA and then injecting it, maybe into TOSCA metadata. Or it can be a "last tested" timestamp, etc.
So, again, my point is that variability it is inevitable and it's perhaps worthwhile to at least address it, if not support it, in our specs. (Puccini does talk about it in its
FAQ.)