Re: [openstack-dev] [neutron] - L3 flavors and issues with use cases for multiple L3 backends

[Neil Jerram]

On 01/02/16 14:11, Kevin Benton wrote:
> Hi all,
>
> I've been working on an implementation of the multiple L3 backends
> RFE[1] using the flavor framework and I've run into some snags with the
> use-cases.[2]

Is there any good documentation for flavors yet?  I recall looking 
unsuccessfully, a few months ago.

Neil


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Re: [openstack-dev] [neutron] - L3 flavors and issues with use cases for multiple L3 backends

[Eichberger, German]

Not that you could call it scheduling. The intent was that the user could pick 
the best flavor for his task (e.g. a gold router as opposed to a silver one). 
The system then would “schedule” the driver configured for gold or silver. 
Rescheduling wasn’t really a consideration…

German

From: Doug Wiegley 
>
Reply-To: "OpenStack Development Mailing List (not for usage questions)" 
>
Date: Monday, February 1, 2016 at 8:17 PM
To: "OpenStack Development Mailing List (not for usage questions)" 
>
Subject: Re: [openstack-dev] [neutron] - L3 flavors and issues with use cases 
for multiple L3 backends

Yes, scheduling was a big gnarly wart that was punted for the first pass. The 
intention was that any driver you put in a single flavor had equivalent 
capabilities/plumbed to the same networks/etc.

doug


On Feb 1, 2016, at 7:08 AM, Kevin Benton 
> wrote:


Hi all,

I've been working on an implementation of the multiple L3 backends RFE[1] using 
the flavor framework and I've run into some snags with the use-cases.[2]

The first use cases are relatively straightforward where the user requests a 
specific flavor and that request gets dispatched to a driver associated with 
that flavor via a service profile. However, several of the use-cases are based 
around the idea that there is a single flavor with multiple drivers and a 
specific driver will need to be used depending on the placement of the router 
interfaces. i.e. a router cannot be bound to a driver until an interface is 
attached.

This creates some painful coordination problems amongst drivers. For example, 
say the first two networks that a user attaches a router to can be reached by 
all drivers because they use overlays so the first driver chosen by the 
framework works  fine. Then the user connects to an external network which is 
only reachable by a different driver. Do we immediately reschedule the entire 
router at that point to the other driver and interrupt the traffic between the 
first two networks?

Even if we are fine with a traffic interruption for rescheduling, what should 
we do when a failure occurs half way through switching over because the new 
driver fails to attach to one of the networks (or the old driver fails to 
detach from one)? It would seem the correct API experience would be switch 
everything back and then return a failure to the caller trying to add an 
interface. This is where things get messy.

If there is a failure during the switch back, we now have a single router's 
resources smeared across two drivers. We can drop the router into the ERROR 
state and re-attempt the switch in a periodic task, or maybe just leave it 
broken.

How should we handle this much orchestration? Should we pull in something like 
taskflow, or maybe defer that use case for now?

What I want to avoid is what happened with ML2 where error handling is still a 
TODO in several cases. (e.g. Any post-commit update or delete failures in 
mechanism drivers will not trigger a revert in state.)

1. https://bugs.launchpad.net/neutron/+bug/1461133
2. 
https://etherpad.openstack.org/p/neutron-modular-l3-router-plugin-use-cases

--
Kevin Benton

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Re: [openstack-dev] [neutron] - L3 flavors and issues with use cases for multiple L3 backends

[Kevin Benton]

Choosing from multiple drivers for the same flavor is scheduling. I didn't
mean automatically selecting other flavors.
On Feb 2, 2016 17:53, "Eichberger, German" 
wrote:

> Not that you could call it scheduling. The intent was that the user could
> pick the best flavor for his task (e.g. a gold router as opposed to a
> silver one). The system then would “schedule” the driver configured for
> gold or silver. Rescheduling wasn’t really a consideration…
>
> German
>
> From: Doug Wiegley >
> Reply-To: "OpenStack Development Mailing List (not for usage questions)" <
> openstack-dev@lists.openstack.org >>
> Date: Monday, February 1, 2016 at 8:17 PM
> To: "OpenStack Development Mailing List (not for usage questions)" <
> openstack-dev@lists.openstack.org >>
> Subject: Re: [openstack-dev] [neutron] - L3 flavors and issues with use
> cases for multiple L3 backends
>
> Yes, scheduling was a big gnarly wart that was punted for the first pass.
> The intention was that any driver you put in a single flavor had equivalent
> capabilities/plumbed to the same networks/etc.
>
> doug
>
>
> On Feb 1, 2016, at 7:08 AM, Kevin Benton > wrote:
>
>
> Hi all,
>
> I've been working on an implementation of the multiple L3 backends RFE[1]
> using the flavor framework and I've run into some snags with the
> use-cases.[2]
>
> The first use cases are relatively straightforward where the user requests
> a specific flavor and that request gets dispatched to a driver associated
> with that flavor via a service profile. However, several of the use-cases
> are based around the idea that there is a single flavor with multiple
> drivers and a specific driver will need to be used depending on the
> placement of the router interfaces. i.e. a router cannot be bound to a
> driver until an interface is attached.
>
> This creates some painful coordination problems amongst drivers. For
> example, say the first two networks that a user attaches a router to can be
> reached by all drivers because they use overlays so the first driver chosen
> by the framework works  fine. Then the user connects to an external network
> which is only reachable by a different driver. Do we immediately reschedule
> the entire router at that point to the other driver and interrupt the
> traffic between the first two networks?
>
> Even if we are fine with a traffic interruption for rescheduling, what
> should we do when a failure occurs half way through switching over because
> the new driver fails to attach to one of the networks (or the old driver
> fails to detach from one)? It would seem the correct API experience would
> be switch everything back and then return a failure to the caller trying to
> add an interface. This is where things get messy.
>
> If there is a failure during the switch back, we now have a single
> router's resources smeared across two drivers. We can drop the router into
> the ERROR state and re-attempt the switch in a periodic task, or maybe just
> leave it broken.
>
> How should we handle this much orchestration? Should we pull in something
> like taskflow, or maybe defer that use case for now?
>
> What I want to avoid is what happened with ML2 where error handling is
> still a TODO in several cases. (e.g. Any post-commit update or delete
> failures in mechanism drivers will not trigger a revert in state.)
>
> 1. https://bugs.launchpad.net/neutron/+bug/1461133
> 2. https://etherpad.openstack.org/p/<
> https://etherpad.openstack.org/p/neutron-modular-l3-router-plugin-use-cases
> >neutron-modular-l3-router-plugin-use-cases<
> https://etherpad.openstack.org/p/neutron-modular-l3-router-plugin-use-cases
> >
>
> --
> Kevin Benton
>
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[openstack-dev] [neutron] - L3 flavors and issues with use cases for multiple L3 backends

[Kevin Benton]

Hi all,

I've been working on an implementation of the multiple L3 backends RFE[1]
using the flavor framework and I've run into some snags with the
use-cases.[2]

The first use cases are relatively straightforward where the user requests
a specific flavor and that request gets dispatched to a driver associated
with that flavor via a service profile. However, several of the use-cases
are based around the idea that there is a single flavor with multiple
drivers and a specific driver will need to be used depending on the
placement of the router interfaces. i.e. a router cannot be bound to a
driver until an interface is attached.

This creates some painful coordination problems amongst drivers. For
example, say the first two networks that a user attaches a router to can be
reached by all drivers because they use overlays so the first driver chosen
by the framework works  fine. Then the user connects to an external network
which is only reachable by a different driver. Do we immediately reschedule
the entire router at that point to the other driver and interrupt the
traffic between the first two networks?

Even if we are fine with a traffic interruption for rescheduling, what
should we do when a failure occurs half way through switching over because
the new driver fails to attach to one of the networks (or the old driver
fails to detach from one)? It would seem the correct API experience would
be switch everything back and then return a failure to the caller trying to
add an interface. This is where things get messy.

If there is a failure during the switch back, we now have a single router's
resources smeared across two drivers. We can drop the router into the ERROR
state and re-attempt the switch in a periodic task, or maybe just leave it
broken.

How should we handle this much orchestration? Should we pull in something
like taskflow, or maybe defer that use case for now?

What I want to avoid is what happened with ML2 where error handling is
still a TODO in several cases. (e.g. Any post-commit update or delete
failures in mechanism drivers will not trigger a revert in state.)

1. https://bugs.launchpad.net/neutron/+bug/1461133
2. https://etherpad.openstack.org/p/

neutron-modular-l3-router-plugin-use-cases


-- 
Kevin Benton
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Re: [openstack-dev] [neutron] - L3 flavors and issues with use cases for multiple L3 backends

[Doug Wiegley]

Yes, scheduling was a big gnarly wart that was punted for the first pass. The 
intention was that any driver you put in a single flavor had equivalent 
capabilities/plumbed to the same networks/etc.

doug


> On Feb 1, 2016, at 7:08 AM, Kevin Benton  wrote:
> 
> Hi all,
> 
> I've been working on an implementation of the multiple L3 backends RFE[1] 
> using the flavor framework and I've run into some snags with the use-cases.[2]
> 
> The first use cases are relatively straightforward where the user requests a 
> specific flavor and that request gets dispatched to a driver associated with 
> that flavor via a service profile. However, several of the use-cases are 
> based around the idea that there is a single flavor with multiple drivers and 
> a specific driver will need to be used depending on the placement of the 
> router interfaces. i.e. a router cannot be bound to a driver until an 
> interface is attached.
> 
> This creates some painful coordination problems amongst drivers. For example, 
> say the first two networks that a user attaches a router to can be reached by 
> all drivers because they use overlays so the first driver chosen by the 
> framework works  fine. Then the user connects to an external network which is 
> only reachable by a different driver. Do we immediately reschedule the entire 
> router at that point to the other driver and interrupt the traffic between 
> the first two networks?
> 
> Even if we are fine with a traffic interruption for rescheduling, what should 
> we do when a failure occurs half way through switching over because the new 
> driver fails to attach to one of the networks (or the old driver fails to 
> detach from one)? It would seem the correct API experience would be switch 
> everything back and then return a failure to the caller trying to add an 
> interface. This is where things get messy.
> 
> If there is a failure during the switch back, we now have a single router's 
> resources smeared across two drivers. We can drop the router into the ERROR 
> state and re-attempt the switch in a periodic task, or maybe just leave it 
> broken.
> 
> How should we handle this much orchestration? Should we pull in something 
> like taskflow, or maybe defer that use case for now?
> 
> What I want to avoid is what happened with ML2 where error handling is still 
> a TODO in several cases. (e.g. Any post-commit update or delete failures in 
> mechanism drivers will not trigger a revert in state.)
> 
> 1. https://bugs.launchpad.net/neutron/+bug/1461133 
> 
> 2. https://etherpad.openstack.org/p/ 
> neutron-modular-l3-router-plugin-use-cases
>  
> -- 
> Kevin Benton
> 
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