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I pretty much completely agree with Stephen here, other than believing we should do N:1 on VIPs (item 2 in your list) from the start. We know we're doing IPv6 this way, and I'd rather not put off support for it at the controller/driver/whatever layer just because the underlying infrastructure isn't there yet. I'd like to be 100% ready when it is, not wait until the network is ready and then do a refactor.

--Adam

https://keybase.io/rm_you


From: Stephen Balukoff <sbalukoff at bluebox.net<mailto:sbalukoff at bluebox.net>>
Reply-To: "OpenStack Development Mailing List (not for usage questions)" <openstack-dev at lists.openstack.org<mailto:openstack-dev at lists.openstack.org>>
Date: Monday, September 15, 2014 1:33 PM
To: "OpenStack Development Mailing List (not for usage questions)" <openstack-dev at lists.openstack.org<mailto:openstack-dev at lists.openstack.org>>
Subject: Re: [openstack-dev] [Octavia] Responsibilities for controller drivers

Hi Brandon!

My responses in-line:

On Fri, Sep 12, 2014 at 11:27 AM, Brandon Logan <brandon.logan at rackspace.com<mailto:brandon.logan at rackspace.com>> wrote:
IN IRC the topic came up about supporting many-to-many load balancers to
amphorae.  I believe a consensus was made that allowing only one-to-many
load balancers to amphorae would be the first step forward, and
re-evaluate later, since colocation and apolocation will need to work
(which brings up another topic, defining what it actually means to be
colocated: On the same amphorae, on the same amphorae host, on the same
cell/cluster, on the same data center/availability zone. That should be
something we discuss later, but not right now).

I am fine with that decisions, but Doug brought up a good point that
this could very well just be a decision for the controller driver and
Octavia shouldn't mandate this for all drivers.  So I think we need to
clearly define what decisions are the responsibility of the controller
driver versus what decisions are mandated by Octavia's construct.

In my mind, the only thing dictated by the controller to the driver here would be things related to colocation / apolocation. So in order to fully have that discussion here, we first need to have a conversation about what these things actually mean in the context of Octavia and/or get specific requirements from operators here.  The reference driver (ie. haproxy amphora) will of course have to follow a given behavior here as well, and there's the possibility that even if we don't dictate behavior in one way or another, operators and users may come to expect the behavior of the reference driver here to become the defacto requirements.


Items I can come up with off the top of my head:

1) LB:Amphora - M:N vs 1:N

My opinion:  For simplicity, first revision should be 1:N, but leave open the possibility of M:N at a later date, depending on what people require. That is to say, we'll only do 1:N at first so we can have simpler scheduling algorithms for now, but let's not paint ourselves into a corner in other portions of the code by assuming there will only ever be one LB on an amphora.

2) VIPs:LB - M:N vs 1:N

So, I would revise that to be N:1 or 1:1. I don't think we'll ever want to support a case where multiple LBs share the same VIP. (Multiple amphorae per VIP, yes... but not multiple LBs per VIP. LBs are logical constructs that also provide for good separation of concerns, particularly around security.)

The most solid use case for N:1 that I've heard is the IPv6 use case, where a user wants to expose the exact same services over IPv4 and IPv6, and therefore it makes sense to be able to have multiple VIPs per load balancer. (In fact, I'm not aware of other use cases here that hold any water.) Having said this, we're quite a ways from IPv6 being ready for use in the underlying networking infrastructure.  So...  again, I would say let's go with 1:1 for now to make things simple for scheduling, but not paint ourselves into a corner here architecturally in other areas of the code by assuming there will only ever be one VIP per LB.

3) Pool:HMs - 1:N vs 1:1

Does anyone have a solid use case for having more than one health monitor per pool?  (And how do you resolve conflicts in health monitor check results?)  I can't think of one, so 1:1 has my vote here.



I'm sure there are others.  I'm sure each one will need to be evaluated
on a case-by-case basis.  We will be walking a fine line between
flexibility and complexity.  We just need to define how far over that
line and in which direction we are willing to go.

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