Open Stack

From: Salvatore Orlando <sorlando at nicira.com<mailto:sorlando at nicira.com>>
Reply-To: "OpenStack Development Mailing List (not for usage questions)" <openstack-dev at lists.openstack.org<mailto:openstack-dev at lists.openstack.org>>
Date: Thursday, February 12, 2015 at 8:36 AM
To: OpenStack Development Mailing List <openstack-dev at lists.openstack.org<mailto:openstack-dev at lists.openstack.org>>
Subject: [openstack-dev] [Neutron] Update on "DB" IPAM driver

Hi,

I have updated the patch; albeit not complete yet it's kind of closer to be an allocator decent enough to replace the built-in logic.

I will be unable to attend today's L3/IPAM meeting due to a conflict, so here are some highlights from me on which your feedback is more than welcome:

- I agree with Carl that the IPAM driver should not have explicit code paths for autoaddress subnets, such as DHCPv6 stateless ones. In that case, the consumer of the driver will generate the address and then to the IPAM driver that would just be allocation of a specific address. However, I have the impression the driver still needs to be aware of whether the subnet has an automatic address mode or not - since in this case 'any' address allocation won't be possible. There already comments about this in the review [1]

I think the auto-generated case should be a base class as you described in [1], but each subclass would implement the specific auto-generation. See the discussion at line 468 in [2] and see what you think. Of course for addresses that come from RA there would be no IPAM.

[1] https://review.openstack.org/#/c/150485/
[2] https://review.openstack.org/#/c/153236/2/neutron/db/db_base_plugin_v2.py,unified


- We had a discussion last week on whether the IPAM driver and neutron should 'share' database tables. I went back and forth a lot of time, but now to me it seems the best thing to do is to have the IPAM driver maintain an 'ip_requests' tables, where it stores allocation info. This table partially duplicates data in IPAllocation, but on the plus side it makes the IPAM driver self sufficient. The next step would be to decide whether we want to go a step further and also assume the driver should not access at all Neutron's DB, but I would defer that discussion to the next iteration (for both the driver and the IPAM interface)

- I promised a non blocking algorithm for IP allocation. The one I was developing was based on specifying the primary key on the ip_requests table in a way that it would prevent two concurrent requests from getting the same address, and would just retry getting an address until the primary key constraint was satisfied. However, recent information emerged on MySQL galera's (*) data set [2] certification  clarified that this kind of algorithm would still result in a deadlock error from failed data set certification. It is worth noting that in this case a solution based on traditional compare-and-swap is not possible because concurrent requests would be inserting data at the same time. I am now working on an alternative solution, and I would like to first implement a PoC for it (so that I can prove it works).

- The db base refactoring being performed by Pavel is under way [3]. It is worth noting that this is a non-negligible change to some of Neutron's basic and more critical workflows. We should expect pushback from the community regarding the introduction of this change in the 3rd milestone. At this stage I would suggest either:
A) consider a strategy for running pluggable IPAM as optional
B) consider delaying to Liberty.
(and that's where I get virtually jeered and pelted with rotten tomatoes)

I wish I had some old tomatoes! Seriously, I think "A" is a reasonable approach. To make this really explicit we may want to basically replace the DB plugin class with a shim that delegates to either the current implementation or the new implementation, depending on the flag.


Thanks for reading this post,
Salvatore

[1] https://review.openstack.org/#/c/150485/
[2] http://lists.openstack.org/pipermail/openstack-dev/2015-February/056007.html
[3] https://review.openstack.org/#/c/153236/
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