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Thanks, that cleared it up for me.

Staying on the topic of multi-nics, I have been trying to understand the
direction in which Nova is going in regards to networking, and reading up on
the multi-nics blueprint, it certainly seems like it's going in the right
direction, but I do have one question:

What was the reasoning behind associating networks, and not NICs, to an
instance?  I understand that each instance NIC would belong to a distinct
network, but it just seems more intuitive to imagine that an instance has
NICs, and these NICs are connected to networks(or even more intuitively,
connected to virtual ports that belong to various networks - Assigning a
port to a NIC is like allocating an IP address).

One problem I see from my suggestion above is that there is no association
between NICs and networks, which means there is no way to select a network
to grab an IP address from for each NIC at the time of VM launch.  I might
be missing something completely here, but why not just let the user manage
all this through the management  API before the VM launch?  Let the user
create NICs, Networks(and Ports with IP addresses), and map the NICs to
ports.  Then pass this list of 'connected' NICs as a parameter to launch a
VM.  This parameter is optional, and if omitted, it should be treated as
launching a single NIC instance, with a new NIC created and associated with
the instance on the fly.  This prevents it from breaking the way it works
now.

If the concept of NICs for instance makes sense to everyone, I would love to
help out and look further into what work needs to be done to extend the
current multi-nic model into this one.

I hope this made sense.  I apologize for the length.

Thanks,
Ryu


On Tue, Mar 29, 2011 at 12:47 AM, Trey Morris <trey.morris at rackspace.com>wrote:

> I've written a migration to handle moving the data in the current instances
> table mac_address column into the new mac_address table before the column is
> removed.
>
> I agree with Jay, data should never be discarded when migrating forward. I
> don't think there has been a case yet where data is migrated in nova. This
> could be the first.
>
> -trey
>
> On Mon, Mar 28, 2011 at 8:17 AM, Jay Pipes <jaypipes at gmail.com> wrote:
>
>> On Mon, Mar 28, 2011 at 2:31 AM, Ishimoto, Ryu <ryu at midokura.jp> wrote:
>> > Hi All,
>> > I was looking at the multi-nic
>> > blueprint(https://blueprints.launchpad.net/nova/+spec/nova-multi-nic),
>> and
>> > in particular:
>> > 1) removing mac_address column from the instances table and creating a
>> > mac_addresses table. This is for storing which instances own which mac
>> > addresses as well as which network each mac is for.
>> > What happens(or should happen) to the MAC addresses that are already
>> > associated with instances?  Will they be migrated to the new
>> mac_addresses
>> > table?  Or will they be discarded completely?
>>
>> Data should never be discarded in situations like this where a column
>> is moved to another table's schema (or to be records in another
>> table).
>>
>> > I was curious to know how Nova usually handles data migration issues
>> like
>> > this.
>>
>> No idea whether/if Nova's data migrations have previously needed to
>> preserve data in this way. Glance does, however, and you can use the
>> following Python changescript to get an idea how to perform this exact
>> type of change:
>>
>>
>> http://bazaar.launchpad.net/~glance-core/glance/cactus-trunk/view/head:/glance/registry/db/migrate_repo/versions/003_add_disk_format.py
>>
>> Note that SQLite has issues if you try to add and drop columns in the
>> same changescript and you also have an unrelated column that is
>> indexed (see:
>> http://code.google.com/p/sqlalchemy-migrate/issues/detail?id=117).
>> If this is the case, you will need to write SQL-based changescripts
>> specfically for SQLite. You can see examples of how this is
>> accomplished in Glance for the same DB version here:
>>
>>
>> http://bazaar.launchpad.net/~glance-core/glance/cactus-trunk/view/head:/glance/registry/db/migrate_repo/versions/003_sqlite_upgrade.sql
>>
>> http://bazaar.launchpad.net/~glance-core/glance/cactus-trunk/view/head:/glance/registry/db/migrate_repo/versions/003_sqlite_downgrade.sql
>>
>> Cheers,
>> jay
>>
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