feature suggestion: migration network

[Dan Kenigsberg]

On Sun, Jan 13, 2013 at 07:47:59AM -0500, Simon Grinberg wrote:

<snip>

> I think for the immediate terms the most compelling is the external network provider use case, where you want to allow the external network management to rout/shape the traffic per tenant, something that will be hard to do if all is aggregated on the host.
>  
> But coming to think of it, I like more and more the idea of having migration network as part of the VM configuration. It's both simple to do now and later add logic on top if required, and VDSM supports that already now. 
> 
> So:
> 1. Have a default migration network per cluster (default is the management network as before)
> 2. This is the default migration network for all VMs created in that cluster
> 3. Allow in VM properties to override this (Tenant use case, and supports the external network manager use case)
> 4. Allow from the migration network to override as well. 
> 
> Simple, powerful, flexible, while the logic is not complicated since the engine has nothing to decide - everything is orchestrated by the admin while initial out of the box setup is very simple (one migration network for all which is by default the management network). 
> 
> Later you may apply policies on top of this. 
> 
> Thoughts? 

I'm not sure that multiple migration networks is an urgent necessity,
but what you suggest seems simple indeed.

Simple because each VM has exactly ONE choice for a migration network.
The multiplicity is for separation, not for automatic redundancy. An
admin may manually split his VMs among migration networks, but no
scheduling logic is required from Engine. If the migration network is
unavailable for some reason, no migration would take place.

We should design the solution with N networks in mind, and at worse, if we
feel that the UI is needlessly cluttered we can limit to N=1.

If there are no objections let's do it this way:
- add a new network role of migration network.
- add a per-cluster property of defaultMigrationNetwork. Its factory
  default is ovirtmgmt, for backward compatibility.
- add a per-VM propery of migrationNetwork. If Null, the cluster
  defaultMigrationNetwork would be used.

Dan.