SR-IOV guide for OVN¶
The purpose of this page is to describe how SR-IOV works with OVN. Prior to reading this document, it is recommended to first read the basic guide for SR-IOV.
External ports¶
In order for SR-IOV to work with the
Neutron driver we are leveraging the external ports
feature from the OVN project. When virtual machines are booted
on hypervisors supporting SR-IOV nics, the local ovn-controllers are
unable to reply to the VM’s DHCP, internal DNS, IPv6 router solicitation
requests, etc… since the hypervisor is bypassed in the SR-IOV case. OVN
then introduced the idea of having external
ports which are able to
reply on behalf of those VM ports external to the hypervisor that they
are running on.
The OVN Neutron driver will create a port of the type external
for ports with the following VNICs set:
direct
direct-physical
macvtap
Also, ports of the type external
will be scheduled on the gateway
nodes (controller or networker nodes) in HA mode by the OVN Neutron
driver. Check the OVN Database information section for more
information.
Environment setup for OVN SR-IOV¶
There are a very few differences between setting up an environment for SR-IOV for the OVS and OVN Neutron drivers. As mentioned at the beginning of this document, the instructions from the the basic guide for SR-IOV are required for getting SR-IOV working with the OVN driver.
The only differences required for an OVN deployment are:
When configuring the
mechanism_drivers
in the ml2_conf.ini file we should specifyovn
driver instead of theopenvswitch
driverDisabling the Neutron DHCP agent
Deploying the OVN Metadata agent on the gateway nodes (controller or networker nodes)
OVN Database information¶
Before getting into the ports information, the previous sections
talks about gateway nodes, the OVN Neutron driver identifies
a gateway node by the ovn-cms-options=enable-chassis-as-gw
and
ovn-bridge-mappings
options in the external_ids column from the
Chassis
table in the OVN Southbound database:
$ ovn-sbctl list Chassis
_uuid : 12b13aff-a821-4cde-a4ac-d9cf8e2c91bc
external_ids : {ovn-cms-options=enable-chassis-as-gw, ovn-bridge-mappings="public:br-ex", ...}
hostname : controller-0
name : "1a462946-ccfd-46a6-8abf-9dca9eb558fb"
...
For more information about both of these options, please take a look at the ovn-controller documentation.
These options can be set by running the following command locally on each
gateway node (note, the ovn-bridge-mappings
will need to be adapted
to your environment):
$ ovs-vsctl set Open_vSwitch . external-ids:ovn-cms-options=\"enable-chassis-as-gw\" external-ids:ovn-bridge-mappings=\"public:br-ex\"
As mentioned in the External ports section, every time a Neutron port
with a certain VNIC is created the OVN driver will create a port of the
type external
in the OVN Northbound database. These ports can be
found by issuing the following command:
$ ovn-nbctl find Logical_Switch_Port type=external
_uuid : 105e83ae-252d-401b-a1a7-8d28ec28a359
ha_chassis_group : [43047e7b-4c78-4984-9788-6263fcc69885]
type : external
...
The ha_chassis_group
column indicates which HA Chassis Group that
port belongs to, to find that group do:
# The UUID is the one from the ha_chassis_group column from
# the Logical_Switch_Port table
$ ovn-nbctl list HA_Chassis_Group 43047e7b-4c78-4984-9788-6263fcc69885
_uuid : 43047e7b-4c78-4984-9788-6263fcc69885
external_ids : {}
ha_chassis : [3005bf84-fc95-4361-866d-bfa1c980adc8, 72c7671e-dd48-4100-9741-c47221672961]
name : neutron-4b2944ca-c7a3-4cf6-a9c8-6aa541a20535
Note
The external ports will be placed on a HA Chassis Group for the
network that the port belongs to. Those HA Chassis Groups are named as
neutron-<Neutron Network UUID>
, as seeing in the output above. You
can also use this “name” with the ovn-nbctl list
command when
searching for a specific HA Chassis Group.
The chassis that are members of the HA Chassis Group are listed in
the ha_chassis
column. Those are the gateway nodes (controller
or networker nodes) in the deployment and it’s where the external
ports will be scheduled. In order to find which gateway node the external
ports are scheduled on use the following command:
# The UUIDs are the UUID members of the HA Chassis Group
# (ha_chassis column from the HA_Chassis_Group table)
$ ovn-nbctl list HA_Chassis 3005bf84-fc95-4361-866d-bfa1c980adc8 72c7671e-dd48-4100-9741-c47221672961
_uuid : 3005bf84-fc95-4361-866d-bfa1c980adc8
chassis_name : "1a462946-ccfd-46a6-8abf-9dca9eb558fb"
external_ids : {}
priority : 32767
_uuid : 72c7671e-dd48-4100-9741-c47221672961
chassis_name : "a0cb9d55-a6da-4f84-857f-d4b674088c8c"
external_ids : {}
priority : 32766
Note the priority
column from the previous command, the chassis with
the highest priority
from that list is the chassis that will have
the external ports scheduled on it. In our example above, the chassis
with the UUID 1a462946-ccfd-46a6-8abf-9dca9eb558fb
is the one.
Whenever the chassis with the highest priority goes down, the ports will be automatically scheduled on the next chassis with the highest priority which is alive. So, the external ports are HA out of the box.
Known limitations¶
The current SR-IOV implementation for the OVN Neutron driver has a few known limitations that should be addressed in the future:
Routing on VLAN tenant network will not work with SR-IOV. This is because the external ports are not being co-located with the logical router’s gateway ports, for more information take a look at bug #1875852.