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Re: [libvirt] migration of vnlink VMs
- From: Laine Stump <laine laine org>
- To: libvir-list redhat com
- Subject: Re: [libvirt] migration of vnlink VMs
- Date: Fri, 29 Apr 2011 08:45:50 -0400
On 04/28/2011 04:15 AM, Oved Ourfalli wrote:
From: "Laine Stump"<lstump redhat com
On 04/27/2011 09:58 AM, Oved Ourfalli wrote:
We read your proposal for abstraction of guest<--> host network
connection in libvirt.
You has an open issue there regarding the vepa/vnlink attributes:
"3) What about the parameters in the<virtualport> element that are
currently used by vepa/vnlink. Do those belong with the host, or
with the guest?"
The parameters for the virtualport element should be on the guest,
and not the host, because a specific interface can run multiple
Are you talking about host interface or guest interface? If you mean
that multiple different profiles can be used when connecting to a
particular switch - as long as there are only a few different
rather than each guest having its own unique profile, then it still
seems better to have the port profile live with the network definition
(and just define multiple networks, one for each port profile).
The profile names can be changed regularly, so it looks like it will be better to put them in the guest level, so that the network host file won't have to be changed on all hosts once something has changed in the profiles.
Also, you will have a duplication of data, writing all the profile name on all the hosts that are connected to the vn-link/vepa switch.
But is it potentially the same for many/all guests, or is it necessarily
different for every guest? If it's the former, then do you have more
guests, or more hosts?
so it will be a mistake to define a profile to be interface
specific on the host. Moreover, putting it in the guest level will
enable us in the future (if supported by libvirt/qemu) to migrate
a vm from a host with vepa/vnlink interfaces, to another host with
a bridge, for example.
It seems to me like doing exactly the opposite would make it easier to
migrate to a host that used a different kind of switching (from vepa
vnlink, or from a bridged interface to vepa, etc), since the port
profile required for a particular host's network would be at the host
waiting to be used.
You are right, but we would want to have the option to prevent that from happening in case we wouldn't want to allow it.
We can make the ability to migrate between different network types configurable, and we would like an easy way to tell libvirt - "please allow/don't allow it".
I *think* what you're getting at is this situation:
HostA has a group of interfaces that are connected to a vepa-capable
switch, HostB has a group of interfaces connected to a vnlink-capable
switch. Guest1 is allowed to connect either via a vnlink switch or a
vepa switch, but Guest2 should only use vepa.
In that case, HostA would have a network that had a pool of interfaces
and type "vepa", while HostB would have a pool of interfaces and a type
"vnlink". Guest1 could be accommodated by giving both networks the same
name, or Guest2 could be accommodated by giving each network a different
name (when migrating, if the dest. host doesn't have the desired
network, the migration would fail). However, using just the network
naming, it wouldn't be possible to allow both.
I don't think keeping the virtualport parameters only with the guest
would help (or hurt) this though. What would be needed would be to have
the information about network type *optionally* specified in the guest
interface config (as well as in the network config); if present the
migration would only succeed if the given network on the dest host
matched the given type (and parameters, if any) in the guest config.
So, in the networks at the host level you will have:
And in the guest you will have (for vepa):
<parameters managerid="11" typeid="1193047" typeidversion="2"
Or (for vnlink):
What would the interface for a 2nd guest of each type look like? Could
it be identical? Or might some parameters change for every single guest?
Perhaps it would be best to have virtualport parameters on both network
and guest interface XML, and merge the two to arrive at what's used (the
network definition could contain all the attributes that would be common
to all guests using that network on that host, and the guest interface
definition would contain extra parameters specific to that host. In the
case of a parameter being specified in both places, if they were not
identical, the migration would fail).
This illustrates the problem I was wondering about - in your example
would not be possible for the guest to migrate from the host using a
vepa switch to the host using a vnlink switch (and it would be
You are right. When trying to migrate between vepa and vnlink there will be missing attributes in each in case we leave it on the host.
(you mean if we leave the config on the *guest*, I guess...)
to migrate to a host using a standard bridge only if the virtualport
element was ignored). If the virtualport element lived with the
definition of red-network on each host, it could be migrated without
The only problematic thing would be if any of the attributes within
<parameters> was unique for each guest (I don't know anything about
individual attributes, but "instanceid" sounds like it might be
different for each guest).
Then, when migrating from a vepa/vnlink host to another vepa/vnlink
host containing red-network, the profile attributes will be
available at the guest domain xml.
In case the target host has a red-network, which isn't vepa/vnlink,
we want to be able to choose whether to make the use of the profile
attributes optional (i.e., libvirt won't fail in case of migrating
to a network of another type), or mandatory (i.e., libvirt will fail
in case of migration to a non-vepa/vnlink network).
We have something similar in CPU flags:
<topology sockets="S" cores="C" threads="T"/>
In this analogy, does "CPU flags" == "mode (vepa/vnlink/bridge)" or
"CPU flags" == "virtualport parameters" ? It seems like what you're
wanting can be satisfied by simply not defining "red-network" on the
hosts that don't have the proper networking setup available (maybe
you *really* want to call it is "red-vnlink-network").
What I meant to say in that is that we would like to have the ability to say if an attribute must me used, or not.
Sure, it sounds useful. Would what I outlined above be sufficient? (It
would allow you to say "this guest must have a vepa network connection"
or "this guest can have any network connection, as long as it's named
"red-network". It *won't* allow saying "this guest must have vepa or
vnlink, bridge is not allowed, even if the network name is the same".
You could also put most of the config with the host network definition,
but allow, eg instanceid to be specified in the guest config.
The issues you mention are indeed interesting. I'm cc-ing libvirt-list to see what other people think.
Putting it on the guest will indeed make it problematic to migrate between networks that need different parameters (vnlink/vepa for example).
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