Open Stack

On Sun, 2023-09-10 at 14:51 +0100, Lucas Alvares Gomes wrote:
> On Sun, Sep 10, 2023 at 4:13 AM Satish Patel <satish.txt at gmail.com> wrote:
> > 
> > Folks,
> > 
> > I am trying to set an availability zone for OVN because skyline UI has a mandatory requirement to have an
> > availability zone otherwise you are not allowed to create a network from skyline GUI.
one thing that skiline and admin s to a lesser degree need to be aware of is that nova AZ, Neutron AZ and cinder AZ
are generally not related to each other. you as an admin can align them but a enduser should not assume that
when creating a vm with a netwok and a voluem that the name of the AZ for all 3 should be the same.
AZs are also optional in all 3 servics that support them. nova invents a fake AZ called "nova" and puts all host
that dont otherwise have an az in it but its considerd a bug to explictly request the nova az.
we have debated makeing that a hard error in future api version although currently we do know that some people do
reueqst the defautl nova az even though we document that you should not.
https://docs.openstack.org/nova/latest/admin/availability-zones.html
"""
The use of the default availability zone name in requests can be very error-prone. Since the user can see the list of
availability zones, they have no way to know whether the default availability zone name (currently nova) is provided
because a host belongs to an aggregate whose AZ metadata key is set to nova, or because there is at least one host not
belonging to any aggregate. Consequently, it is highly recommended for users to never ever ask for booting an instance
by specifying an explicit AZ named nova and for operators to never set the AZ metadata for an aggregate to nova. This
can result is some problems due to the fact that the instance AZ information is explicitly attached to nova which could
break further move operations when either the host is moved to another aggregate or when the user would like to migrate
the instance.
"""

i raise this because i would consider it a bug form a nova point of view if skyline forced you to specyify
an az when booting a vm. i would also consider it a bug in skyline if it forced the same on neutron or cinder
since they are an optional feature. even if its common to configure them the skyline ui should not force you to select
one.


> > 
> > for OVN based deployment only option to set AZ is in ovn-cms-options
> > 
> > # ovs-vsctl set open_vswitch . external_ids:ovn-cms-options="enable-chassis-as-gw,availability-zones=az-0"
> > 
> > Question:
> > 
> > 1. How do I configure in kolla-ansible to override or set ovn-cms-options on only gateway chassis?
> > 2. How does AZ work in OVN because OVN is anyway distributed as per documents, What if I just give foobar AZ name to
> > meet Skyline requirement? Is it going to break anything?
> 
> Answering 2.
> 
> There are two types of availability zones in Neutron: Routers and Networks.
> 
> For Routers, ML2/OVN will schedule the gateway router ports onto the
> nodes belonging to the availability zones provided by the
> --availability-zone-hint parameter, for example:
> 
> $ openstack router create --availability-zone-hint az-0
> --availability-zone-hint az-1 router-0
> 
> For Networks. Since DHCP is distributed in ML2/OVN as you pointed out
> we do not care about scheduling DHCP agents (like ML2/OVS). But there
> are few cases for Network AZ in ML2/OVN that are related to external
> ports [0], these are ports that live on a different host than the
> instance to address use cases such as SR-IOV and Baremetal with
> ML2/OVN.
> 
> You can read more ML2/OVN AZs here:
> https://docs.openstack.org/neutron/latest/admin/ovn/availability_zones.html
> 
> [0] https://docs.openstack.org/neutron/latest/admin/ovn/external_ports.html
> 
> Cheers,
> Lucas
>