Open Stack

Hi everyone,

we will validate in the next weeks the idea i'll describe below. If it
sounds feasible to us i would write up a spec for this for later
implementation.

Setup:
1. Two neutron setups with OVN
2. A OVN-IC setup not managed by any tooling (used manually)

Target setup for a individual project

+-------------------------------------+
|          Transit Switch (ts1)       |
|          172.24.0.0/24              |
+-------------------------------------+
        |                    |
+----------------+   +----------------+
| 172.24.0.10    |   | 172.24.0.11    |
|    Router      |   |    Router      |
| 192.168.0.1    |   | 192.168.1.1    |
+----------------+   +----------------+
        |                    |
+----------------+   +----------------+
|    Network     |   |    Network     |
| 192.168.0.0/24 |   | 192.168.1.0/24 |
+----------------+   +----------------+
        |                    |
+----------------+   +----------------+
|      VM        |   |      VM        |
|  192.168.0.10  |   |  192.168.1.10  |
+----------------+   +----------------+

Main creation workflow of a interconnected network:
1. Create a transit switch in the OVN-IC-NB
2. In each neutron:
   a. Create a new provider network that maps to the transit switch.
      E.g. using `--provider-network-type ovn-ic --provider-phyiscal-network ts1`
   b. Create the internal network and router as always and attach the
      router to the internal network and the provider network

Changes needed in Neutron (from my perspective):
1. Neutron must not touch the resources created by OVN-IC. This might be
   done using two options:
   a. Ignore all resources where `external_ids` does not contain any key
      starting with `neutron`.
   b. Ignore specific resources as defined by individual rules:
      I. ignore all Logical_Router that contain
         `other_config:interconn-ts`
      II. ignore all Logical_Router_Static_Route that contain
         `external_ids:ic-learned-route`
2. Neutron must allow OVN-IC transit switches to be treated as external
   networks. AFAIK this should work in the same way as creating any kind
   of OVN network (so Logical_Switch), but just importing an existing
   Logical_Switch.

>From my perspective with these two changes we should be good to
interconnect two neutron setups with probably minimal changes needed.
This is because OVN-IC would only touch the transit switch (which looks
in the Northbound like a regular Logical_Switch). All other resources
would still be managed by neutron and work as they do now.

I will get back to this discussion and (if appropriate) provide a spec
or this idea, once we had time to validate this on our side (which will
take some weeks).

Thanks
Felix

On Tue, Jul 18, 2023 at 01:23:27PM +0200, Rodolfo Alonso Hernandez wrote:
> Ok, this is being tortuous. First of all: define a strategy. If you are
> going to create the resources in Neutron, define how. I've provided a way
> to do this, find a formal strategy to ground it.
>
> Second: (again) try to find a connection between resources, if you are
> going to use the strategy of creating the resources in Neutron. The
> "Logical_Router_Static_Route" belongs to a router univocally. If that
> router has been created by OpenStack, then you can modify the DB sync
> method to consider learned routes too.
>
> In order to do this, you'll need a set of resources that are going to be
> needed in Neutron, the OVN counterparts and other resources (like
> "Logical_Router_Static_Route") that will be added and will be present in
> OVN and not in Neutron DB. Also you'll need to know how to relate all of
> them.
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