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Hi Salvatore and Eugene,

Responses inline:

On Tue, Jul 15, 2014 at 12:59 PM, Salvatore Orlando <sorlando at nicira.com>
wrote:

> I think I've provided some examples in the review.
>

I was hoping for specific examples. The discussion I've seen so far has
been vague enough that it's difficult to see what people mean. It's also
possible you gave specific examples but these were buried in comments on
previous revisions (one of my biggest gripes with the way Gerrit works. :P
) Could you please give a specific example of what you mean, as well as how
it simplifies the user experience?

However, the point is mostly to simplify usage from a user perspective -
> allowing consumers of the neutron API to use the same flavour object for
> multiple services.
>

Actually, I would argue the having a single flavor valid for several
different services complicates the user experience (and vastly complicates
the operator experience). This is because:

* Flavors are how Operators will provide different service levels, or
different feature sets for similar kinds of service. Users interested in
paying for those services are likely to be more confused if a single flavor
lists features for several different kinds of service.
* Billing becomes more incomprehensible when the same flavor is used for
multiple kinds of service. Users and Operators should not expect to pay the
same rate for a "Gold" FWaaS instance and "Gold" VPNaaS instance, so why
complicate things by putting them under the same flavor?
* Because of the above concerns, it's likely that Operators will only
deploy service profiles in a flavor for a single type of service anyway.
But from the user's perspective, it's not apparent when looking at the list
of flavors, which are valid for which kinds of service. What if a user
tries to deploy a LBaaS service using a flavor that only has FWaaS service
profiles associated with it? Presumably, the system must respond with an
error indicating that no valid service profiles could be found for that
service in that flavor. But this isn't very helpful to the user and is
likely to lead to increased support load for the Operator who will need to
explain this.
* A single-service flavor is going to be inherently easier to understand
than a multi-service flavor.
* Single-service flavors do not preclude the ability for vendors to have
multi-purpose appliances serve multiple roles in an OpenStack cloud.


> There are other considerations which could be made, but since they're
> dependent on features which do not yet exist (NFV, service insertion,
> chaining and steering) I think there is no point in arguing over it.
>

Agreed. Though, I don't think single-service flavors paint us into a corner
here at all. Again, things get complicated enough when it comes to service
insertion, chaining, steering, etc. that what we'll really need at that
point is actual orchestration. Flavors alone will not solve these problems,
and orchestration can work with many single-service flavors to provide the
illusion of multi-service flavors.


> In conclusion I think the idea makes sense, and is a minor twist in the
> current design which should not either make the feature too complex neither
> prevent any other use case for which the flavours are being conceived. For
> the very same reason however, it is worth noting that this is surely not an
> aspect which will cause me or somebody else to put a veto on this work item.
>

I don't think this is a minor twist in the current design, actually:
* We'll have to deal with cases like the above where no valid service
profiles can be found for a given kind of flavor (which we can avoid
entirely if a flavor can have service profiles valid for only one kind of
service).
* When and if tags/capabilities/extensions get introduced, we would need to
provide an additional capabilities list on the service profiles in order to
be able to select which service profiles provide the capabilities requested.
* The above point makes things much more complicated when it comes to
scheduling algorithms for choosing which service profile to use when
multiple can meet the need for a given service. What does 'weight' mean if
all but two low-weight service profiles get eliminated as not suitable?

Another aspect to consider is how the flavours will work when the advanced
> service type they refer to is not consumable through the neutron API, which
> would be the case with an independent load balancing API endpoint. But this
> is probably another story.
>

As far as I'm aware, flavors will only ever apply to advanced services
consumable through the Neutron API. If this weren't the case, what's the
point of having a flavor describing the service at all? If you're talking
about Octavia here--  well, our plan is to have Octavia essentially be an
other load balancer vendor, interfaced through a driver in the Neutron
LBaaS extension. (This is also why so many developers interested in seeing
Octavia come to light are spending all their time right now improving
Neutron LBaaS-- we want it to be feature-rich enough in Juno for us to be
able to actually do interesting things with Octavia without having to
resort to building our own independent API endpoint if at all possible.) If
Octavia ever splits off and has its own API endpoint, it would need to
implement something like the Neutron flavor framework itself-- and in this
case, what we decide to do there should not affect the Neutron flavor
framework at all (or visa versa).

If you want to provide the illusion of two different top-level services /
API endpoints having the same "flavor," then I would say, "that's what
orchestration is for."

On Tue, Jul 15, 2014 at 2:07 PM, Eugene Nikanorov <enikanorov at mirantis.com>
 wrote:

> Hi Stephen,
>
> So, as was discussed, existing proposal has some aspects which better to
> be postponed, like extension list on the flavor (instead of tags).
>

Agreed-- I think we need to more fully flesh out how extension list / tags
should work here before we implement it. But this doesn't prevent us from
rolling forward with a "version 1" of flavors so that we can start to use
some of the benefits of having flavors (like the ability to use multiple
service profiles with a single driver/provider, or multiple service
profiles for a single kind of service).


> Particularly that idea has several drawbacks:
>  - it makes public API inflexible
>  - turning features on/off is not what flavors should be doing, it's a
> task for policy framework and not flavors
>  - flavor-based rest call dispatching is quite complex solution giving no
> benefits for service plugins
>

I'm confused as to what you mean by "that idea" here. Are you taking about
the "extension list"? If this is the case, I agree that that aspect needs
to be refined and should probably be postponed if possible.


> While this is not explicitly written in proposal - that's what implied
> there.
> I think that one is a major blocker of the proposal right now, it deserves
> future discussion and not essential to the problem flavors are supposed to
> solve.
>

Yes, I think there are many benefits we can get out of the flavor framework
without having to have an extensions list / tags at this revision. But I'm
curious: Did we ever define what we were actually trying to solve with
flavors?  Maybe that's the reason the discussion on this has been all of
the place: People are probably making assumptions about the problem we're
trying to solve and we need to get on the same page about this.



> Other than that, I personally don't have much disagreements on the
> proposal.
>
> The question about service type on the flavor is minor IMO. We can allow
> it to be NULL, which would mean multiservice flavor.
> However, multiservice flavors may put some minor requirements to driver
> API (that's mainly because of how flavor plugin interacts with service
> plugins)
>

Yes, I think single-service flavors is almost certainly going to be a
simpler thing to implement, too-- and if we want to get flavors in for Juno
(which I know *we* really want to do), then I think reducing the complexity
here is probably a good idea, at least for the first revision.

 Thanks,
Stephen

-- 
Stephen Balukoff
Blue Box Group, LLC
(800)613-4305 x807
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