[Neutron] PTG summary

Slawek Kaplonski skaplons at redhat.com
Mon Nov 2 21:56:59 UTC 2020


Below is my summary of the Neutron team sessions which we had during the 
virtual PTG last week.
Etherpad with notes from the discussions can be found at [1].

## Retrospective of the Victoria cycle
>From the good things during _Victoria_ cycle team pointed:
* Complete 8 blueprints including the _Metadata over IPv6_ [2],
* Improved feature parity in the OVN driver,
* Good review velocity

>From the not so good things we mentioned:
* CI instability - average number of rechecks needed to merge patch in last 
year can be found at [3],
* Too much "Red Hat" in the Neutron team - and percentage of the reviews (and 
patches) done by people from Red Hat is constantly increasing over last few 
cycles. As a main reason of that we pointed that it is hard to change 
companies way of thinking that dedicating developer to the upstream project 
means that they lose developer in downstream.
* Migration of our CI and Zuul v3 took us a lot of time and effort - but good 
thing is that we accomplished that in the Victoria cycle :)

During that session we also agreed on some action items for the Wallaby cycle:
* keep talking about OVN details - Miguel Lavalle and me will work on some way 
to deliver talks about Neutron OVN backend and OVN internals to the community 
during next months. The idea is to maybe propose some talks ever 6 weeks or 
so. This may make ovn driver development more diverse and let operators to 
thing about migration to the ovn backend.

## Review of the existing meetings
We reviewed list of our existing upstream meetings and discussed about ideas 
on how to increase number of attendees on the meetings.
We decided to:
* drop neutron-qos meeting as it's not needed anymore
* advertise more meetings and meetings' agenda on the OpenStack mailing list - 
I will send reminders with links to the agenda before every meeting
* Together with Lajos Katona we will give some introduction to the debugging 
of CI issues in Neutron*

## Support for old versions
Bernard started discussion about support for the old releases in Neutron and 
Neutron stadium projects.
For Neutron we decided to mark __Ocata__ branch as unmaintained already as its 
gate is already broken.
For the __Pike__ and never branches we will keep them in the __EM__ phase as 
there is still some community interest to keep those branches open.
For the stadium projects we decided to do it similary to what we did while 
looking for new maintainers for the projects. We will send email "call for 
maintainers" for such stable branches. If there will be no voluneers to step 
in, fix gate issues and keep those branches healthy, we will mark them as 
__unmaintained__ and later as __End of Life__ (EOL).
Currently broken CI is in projects:
* networking-sfc,
* networking-bgpvpn/bagpipe,
* neutron-fwaas

And those are candidates to be marked as unmaintained if there will be no 
volunteers to fix them.
Bernard Cafarelli volunteered to work on that in next days/weeks.

## Healtcheck API endpoint
We discussed as our healtcheck API should works. During the discussion we 
decided that:
* healtcheck result should __NOT__ rely on the agents status, it should rely 
on worker's ability to connect to the DB and MQ (rabbitmq)
* Lajos will ask community (API experts) about some guidance how it should 
works on the whole OpenStack level,
* As for reference implementation we can check e.g. Octavia [4] and Keystone 
[5] which already implemented it.

## Squash of the DB migration script
Rodolfo explained us what are benefits of doing such squash of the db migration 
scripts from the old versions:
* Deployment is faster: we don't need to create/delete tables or create+update 
other ones - the win is small possibly in the magnitude of 5s per job,
* DB definition is centralized in one place, not in original definition plus 
further migrations - that is most important reason why we really should do 
* UTs faster: removal of some older checks.

The problem with this may be that we need to do that carefully and be really 
verbose about with such changes we may break stadium projects or 3rd party 
projects which are doing db migration too.
To minimalize potential breakage, we will announce such changes on the 
OpenStack discuss mailing list.
Rodolfo volunteered to take propose squash up to Liberty release in W cycle. 
Together with this squash we will also document that process so in next cycles 
we should be able to do squashes for newer releases in easier way.
Lajos volunteered to help with fixing Neutron stadium projects if that will be 

## Switch to the new engine facade
We were discussing how to move on and finally finish old Blueprint [6]. We 
decided that together with Rodolfo we will try how this new engine facade will 
work without using transaction guards in the code. Hopefully that will let us 
move on with this. If not, we will try to reach out to some DB experts for 
some help with this.

## Change from rootwrap to the privsep
This is now community goal during the Wallaby cycle so we need to focus on it 
to accomplish that transition finally.
This transition may speed up and make our code a bit more secure.
Rodolfo explained us multiple possible strategies of migration:
* move to native, e.g.
  * replace ps with python psutils, not using rootwrap or privsep
  * replace ip commands with pyroute2, under a privsep context (elevated 
permissions needed)
* directly translate rootwrap to privsep, executing the same shell command but 
under a privsep context

To move on with this I will create list of the pieces of code which needs to 
be transitioned in the Neutron repo and in the stadium projects.
Current todo items can be found on the storyboard [7].

## Migration to the NFtables
During this session we were discussing potential strategies on how to migrate 
from the old iptables to the new nftables. We need to start planning that work 
as it major Linux distributions (e.g. RHEL) are planning to deprecate iptables 
in next releases.
It seems that currently all major distros (Ubuntu, Centos, OpenSuSE) supports 
nftables already.
We decided that in Wallaby cycle we will propose new _Manager_ class and we 
will add some config option which will allow people to test new solution.
In next cycles we will continue work on it to make it stable and to make 
upgrade and migration path for users as easy as possible.
There is already created blueprint to track progress on that topic [8].
We need to migrate:
* Linuxbridge firewall, iptables OVS hybrid firewall,
* L3 code (legacy router, DVR router, conntrack, port forwarding),
* iptables metering,
* metadata proxy,
* dhcp agent for when it does metadata for isolated networks and namespace 
* neutron-vpnaas - ipsec code,
* and maybe something else what we didn't found yet.

## Nova-Neutron cross project session
We had very interesting discussion with Nova team. We were discussing topics 
* NUMA affinity in the neutron port
* vhost-vdpa support
* default __vnic_type__/__port flavour__

Notes from that discussion are available in the nova's etherpad [9].

## Neutron scalling issues
At this session we were discussing issues mentioned by operators on the Forum 
sessions a week before the PTG. There was couple of issues mentioned there:
* problems with retries of the DB operations - we should migrate all our code 
to the oslo.db retries mechanism - new blueprint [10] is created to track 
progress on that one.
* problems with maintenance of the agents, like e.g. DHCP or L3 agents - many 
of those issues are caused by how our agents are designed and to really fix 
that we would need very deep and huge changes. But also many of those issues 
can be solved by the __ovn__ backend - **and that is strategic direction in 
which neutron wants to go in the next cycles**,
* Miguel Lavalle and I volunteered to do some profiling of the agents to see 
where we are loosing most of the time - maybe we will be able to find some _low 
hanging fruits_ which can be fixed and improve the situation at least a bit,
* Similar problem with neutron-ovs-agent and especially security groups which 
are using _remove group id_ as a reference - here we also need some volunteers 
who will try to optimize that.

## CI (in)stablility
On Thursday we were discussing how to improve our very poor CI. Finally we 
decided to:
* not recheck patches without giving reason of recheck in the comment - there 
should be already reported bug which should be linked in the _recheck_ 
comment, or user should open new one and link to it also. IN case if the 
problem was e.g. related to infra some simple comment like _infra issue_ will 
also be enough there,
* To lower number of existing jobs we will do some changes like:
  * move *-neutron-lib-master and *-ovs-master jobs to the experimental and 
periodic queues to not run them on every patch,
  * I will switch _neutron-tempest-plugin-api_ job to be deployed with uwsgi 
so we can drop _neutron-tempest-with-uwsgi_ job,
  * Consolidate _neutron-tempest-plugin-scenario-linuxbridge_ and _neutron-
tempest-linuxbridge_ jobs,
  * Consolidate _neutron-tempest-plugin-scenario-iptables_hybrid and _neutron-
tempest-iptables_hybrid jobs,

Later we also discussed about the way how to run or skip tests which can be 
only run when some specific feature is available in the cloud (e.g. _Metadata 
over IPv6_). After some discussion we decided to add new config option with 
list of enabled features. It will be very similar to the existing option 
_api_extensions_. Lajos volunteered to work on that.

As last CI related topic we discussed about testing DVR in our CI. Oleg 
Bondarev volunteered to check and try to fix broken _neutron-tempest-plugin-
dvr-multinode-scenario_ job.

## Flow based DHCP

Liu Yulong raised topic about new way of doing fully distributed DHCP service, 
instead of using _DHCP agent_ on the nodes - RFE is proposed at [11]. His 
proposal of doing Open Flow based DHCP (similar to what e.g. ovn-controller is 
doing) is described in [12]. It could be implemented as an L2 agent extension 
and enabled by operators in the config when they would need it.
As a next step Liu will now propose spec with details about this solution and 
we will continue discussion about it in the spec's review.

## Routed provider networks limited to one host

As a lost topic on Thursday we briefly talked about old RFE [13]. Miguel 
Lavalle told us that his company, Verizon Media, is interested in working on 
this RFE in next cycles. This also involves some work on Nova's side which was 
started by Sylvain Bauza already. Miguel will sync with Sylvain on that RFE.

## L3 feature improvements

On Friday we were discussing some potential improvements in the L3 area. Lajos 
and Bence shown us some features which their company is interested in and on 
which they plan to work. Those are things like:
* support for Bidirectional Forwarding Detection
* some additional API to set additional router parameters like:
  * ECMP max path,
  * ECMP hash algorith
* --provider-allocation-pool parameter in the subnets - in some specific cases 
it may help to use IPs from such _special_ pool for some infrastructure needs, 
more details about that will come in the RFE in future,
For now all those described above improvements are in very early planning 
phase but Bence will sync with Liu and Liu will dedicate some time to discuss 
progress on them during the __L3 subteam meetings__.

## Leveraging routing-on-the-host in Neutron in our next-gen clusters

As a last topic on Friday we were discussing potential solutions of the _L3 on 
the host_ in the Neutron. The idea here is very similar to what e.g. __Calico 
plugin__ is doing currently.
More details about potential solutions are described in the etherpad [14]. 
During the discussion Dawid Deja from OVH told us that OVH is also using very 
similar, downstream only solution.
Conclusion of that discussion was that we may have most of the needed code 
already in Neutron and some stadium projects so as a first step people who are 
interested in that topic, like Jan Gutter, Miguel and Dawid will work on some 
deployment guide for such use case.

## Team photo
During the PTG we also made team photos which You can find at [15].

[1] https://etherpad.opendev.org/p/neutron-wallaby-ptg
[2] https://blueprints.launchpad.net/neutron/+spec/metadata-over-ipv6
[3] https://ibb.co/12sB9N9
[4] https://opendev.org/openstack/octavia/src/branch/master/octavia/api/
[5] https://docs.openstack.org/keystone/victoria/admin/health-check-middleware.html
[6] https://blueprints.launchpad.net/neutron/+spec/enginefacade-switch
[7] https://storyboard.openstack.org/#!/story/2007686
[8] https://blueprints.launchpad.net/neutron/+spec/nftables-migration
[9] https://etherpad.opendev.org/p/nova-wallaby-ptg
[10] https://blueprints.launchpad.net/neutron/+spec/oslo-db-retries
[11] https://bugs.launchpad.net/neutron/+bug/1900934
[12] https://github.com/gotostack/shanghai_ptg/blob/master/
[13] https://bugs.launchpad.net/neutron/+bug/1764738
[14] https://etherpad.opendev.org/p/neutron-routing-on-the-host
[15] http://kaplonski.pl/files/Neutron_virtual_PTG_October_2020.tar.gz

Slawek Kaplonski
Principal Software Engineer
Red Hat

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