On 12/05/2016 10:38 PM, joehuang wrote:
Hello, Brian,
Thank you for your comment, see inline comments marked with [joehuang].
The ASCII figure is not good in the plain text mail, you can check it at the
browser:
http://lists.openstack.org/pipermail/openstack-dev/2016-December/108447.html
Best Regards
Chaoyi Huang (joehuang)
________________________________________
From: Brian Haley [brian.ha...@hpe.com]
Sent: 06 December 2016 10:29
To: OpenStack Development Mailing List (not for usage questions)
Subject: Re: [openstack-dev] [neutron][tricircle]DVR issue in cross Neutron
networking
On 12/5/16 3:03 AM, joehuang wrote:
Hello,
Hi Chaoyi,
Comments inline below.
Tricircle plans to provide L2 network across Neutron to ease supporting
high
availability of application:
For example, in the following figure, the application is consisted of
instance1 and instance2, these two instances will be deployed into two
OpenStack. Intance1 will provide service through "ext net1"(i.e, external
network in OpenStack1), and Instance2 will provide service through
"ext net2". Instance1 and Instance2 will be plugged into same L2 network
net3 for data replication( for example database replication ).
+-----------------+ +-----------------+
|OpenStack1 | |OpenStack2 |
| | | |
| ext net1 | | ext net2 |
| +-----+-----+ | | +-----+-----+ |
| | | | | |
| | | | | |
| +--+--+ | | +--+--+ |
| | | | | | | |
| | R1 | | | | R2 | |
| | | | | | | |
| +--+--+ | | +--+--+ |
| | | | | |
| | | | | |
| +---+-+-+ | | +---+-+-+ |
| net1 | | | net2 | |
| | | | | |
| +--------+--+ | | +--------+--+ |
| | Instance1 | | | | Instance2 | |
| +-----------+ | | +-----------+ |
| | | | | |
| | | net3 | | |
| +------+-------------------------+----+ |
| | | |
+-----------------+ +-----------------+
Are Openstack1 and 2 simply different compute nodes?
[joehuang] No, OpenStack 1 and 2 are two OpenStack clouds, each OpenStack cloud
includes its own services like Nova, Cinder, Neutron. That
means
R1, net1 are network objects in OpenStack cloud1 ( Neutron1)
R2, net2 are network objects in OpenStack cloud2 ( Neutron2),
but net3 will be a shared L2 network existing in both
OpenStack cloud1 and
OpenStack cloud2, i.e in Neutron 1 and Neutron 2.
So net3 is a shared private network, perhaps just a shared VLAN. And something
makes sure IP address allocations don't overlap. Ok.
When we deploy the application in such a way, no matter which part of the
application stops providing service, the other part can still provide
service, and take the workload from the failure one. It'll bring the
failure
tolerance no matter the failure is due to OpenStack crush or upgrade, or
part of the application crush or upgrade.
This mode can work very well and helpful, and router R1 R2 can run in DVR
or legacy mode.
While during the discussion and review of the spec:
https://review.openstack.org/#/c/396564/, in this deployment, the end user
has to add two NICs for each instance, one for the net3(a L2 network across
OpenStack). And the net3 (a L2 network across OpenStack) can not be allowed
to add_router_interface to router R1 R2, this is not good in networking.
If the end user wants to do so, there is DVR MAC issues if more than one L2
network across OpenStack are performed add_router_interface to router
R1 R2.
Let's look at the following deployment scenario:
+-----------------+ +-------------------+
|OpenStack1 | |OpenStack2 |
| | | |
| ext net1 | | ext net2 |
| +-----+-----+ | | +-----+-----+ |
| | | | | |
| | | | | |
| +-------+--+ | | +--+-------+ |
| | | | | | | |
| | R1 | | | | R2 | |
| | | | | | | |
| ++------+--+ | | +--+-----+-+ |
| | | | | | | |
| | | | net3 | | | |
| | -+-+-------------------+-----+--+ | |
| | | | | | | |
| | +--+-------+ | | +-+---------+ | |
| | | Instance1| | | | Instance2 | | |
| | +----------+ | | +-----------+ | |
| | | net4 | | |
| ++-------+--------------------------+---+-+ |
| | | | | |
| +-------+---+ | | +--------+---+ |
| | Instance3 | | | | Instance4 | |
| +-----------+ | | +------------+ |
| | | |
+-----------------+ +-------------------+
net3 and net4 are two L2 network across OpenStacks. These two networks will
be added router interface to R1 R2. Tricircle can help this, and addressed
the DHCP and gateway challenges: different gateway port for the same
network
in different OpenStack, so there is no problem for north-south traffic, the
north-south traffic will goes to local external network directly, for
example,
Instance1->R1->ext net1, instance2->R2->ext net2.
Can you describe the subnet configuration here? Is there just one per
network and was is the IP range?
[joehuang] Subnet in net 3 could be 192.168.1.0, in OpenStack 1, net 3 gateway
IP
192.168.1.254; in OpenStack 2, net 3 gateway IP
192.168.1.253.
Instance 1's IP 192.168.1.3, Instance 2's IP 192.168.1.7,
(Tricircle will help and coordinate the instance IP and
gateway IP allocation)
Subnet in net 4 could be 192.168.2.0, in OpenStack 1, net2
gateway IP
192.168.2.254; in OpenStack 2, net 3 gateway IP
192.168.2.253.
Instance 3's IP 192.168.1.3, Instance 4's IP 192.168.1.7,
(Tricircle will help and coordinate the instance IP and
gateway IP allocation)
The issue is in east-west traffic if R1 R2 are running in DVR mode:
when instance1 tries to ping instance4, DVR MAC replacement will happen
before
the packet leaves the host where the instance1 is running, when the packet
arrives at the host where the instance4 is running, because DVR MAC
replacement,
the source mac(DVR MAC from OpenStack1) of the packet could not be
recognized
in OpenStack2, thus the packet will be dropped, and the ping fails.
So in this case the packet must be routed (L3) since these are different
L2 networks. Typically this would go from Instance1 -> R1 -> Instance4.
But then the return path would be different? Instance4 -> R2 ->
Instance1? It's hard to tell from the diagram. I'm curious if having
both R1 and R2 plugged-into both net3 and net4 is causing problems?
I'll try and configure something similar here, but it might help if you
give a list of the commands you ran to configure neutron here.
[joehuang] The data path is correct: Instance1 -> R1 -> Instance4, return
path: Instance4 -> R2 ->Instance1.
But R1 and R2 are located in two Neutrons. There will be some issue if you
use VxLAN experience this, for VTEP needs to be populated into remote
neutron
(This is another topic). But you can try it using DVR+VLAN, and VLAN range
should
be able to accessible in both Neutron, i.e, in Neutron 1 and Neutron 2,
enable
DVR+VLAN, and manually create net3 and net4 in both neutron with same
VLAN segment.
So is the asymmetric setup causing this? For example, if Instance4 used R1 as
the gateway IP to net3 do things work? I guess I would have to recommend doing
manual changes to the running config to prove it can work, then maybe we can
figure out how to tweak the code.
The latter one deployment bring more flexibility in networking capability,
and don't have to prevent the L2 network across OpenStack from
add_router_interface to DVR mode routers, otherwise, only legacy router
can be
supported for L2 network across OpenStack.
Any thought on how to address this issue to make DVR and L2 network across
OpenStack be able to co-work together?
DVR is really an L3 paradigm although there is some L2 programming going
on so the same MAC can be used across compute nodes. So I'm not sure if
this is a bug you've found or an unsupported configuration.
[joehuang] To be honest, this is not a bug inside one Neutron, only happened
in networking across Neutrons. The scenario is to support application
geo-redundancy:
deploy the application into different OpenStack cloud.
It's interesting to say the least.
-Brian
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