On 01/08/2013 09:04 PM, Dan Kenigsberg wrote:
There's talk about this for ages, so it's time to have proper discussion
and a feature page about it: let us have a "migration" network role, and
use such networks to carry migration data
When Engine requests to migrate a VM from one node to another, the VM
state (Bios, IO devices, RAM) is transferred over a TCP/IP connection
that is opened from the source qemu process to the destination qemu.
Currently, destination qemu listens for the incoming connection on the
management IP address of the destination host. This has serious
downsides: a "migration storm" may choke the destination's management
interface; migration is plaintext and ovirtmgmt includes Engine which
sits may sit the node cluster.
With this feature, a cluster administrator may grant the "migration"
role to one of the cluster networks. Engine would use that network's IP
address on the destination host when it requests a migration of a VM.
With proper network setup, migration data would be separated to that
network.
=== Benefit to oVirt ===
* Users would be able to define and dedicate a separate network for
migration. Users that need quick migration would use nics with high
bandwidth. Users who want to cap the bandwidth consumed by migration
could define a migration network over nics with bandwidth limitation.
* Migration data can be limited to a separate network, that has no
layer-2 access from Engine
=== Vdsm ===
The "migrate" verb should be extended with an additional parameter,
specifying the address that the remote qemu process should listen on. A
new argument is to be added to the currently-defined migration
arguments:
* vmId: UUID
* dst: management address of destination host
* dstparams: hibernation volumes definition
* mode: migration/hibernation
* method: rotten legacy
* ''New'': migration uri, according to
http://libvirt.org/html/libvirt-libvirt.html#virDomainMigrateToURI2 such as
tcp://<ip of migration network on remote node>
If we would like to resolve the migration storm, we also could add the
qemu migration bandwidth limit as a parameter for migrate verb.
Currently, we use it
as a static configuration on vdsm host. It's not flexible. Engine could
pass appropriate parameters according to the traffic load and bandwidth
of migration network.
It also could be specified by customer according to the priority they
suppose.
=== Engine ===
As usual, complexity lies here, and several changes are required:
1. Network definition.
1.1 A new network role - not unlike "display network" should be
added.Only one migration network should be defined on a cluster.
1.2 If none is defined, the legacy "use ovirtmgmt for migration"
behavior would apply.
1.3 A migration network is more likely to be a ''required'' network, but
a user may opt for non-required. He may face unpleasant surprises if he
wants to migrate his machine, but no candidate host has the network
available.
1.4 The "migration" role can be granted or taken on-the-fly, when hosts
are active, as long as there are no currently-migrating VMs.
2. Scheduler
2.1 when deciding which host should be used for automatic
migration, take into account the existence and availability of the
migration network on the destination host.
2.2 For manual migration, let user migrate a VM to a host with no
migration network - if the admin wants to keep jamming the
management network with migration traffic, let her.
3. VdsBroker migration verb.
3.1 For the a modern cluster level, with migration network defined on
the destination host, an additional ''miguri'' parameter should be added
to the "migrate" command
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