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On May 28, 2013, at 8:38 PM, Markus Barth <launchpad.net at boecht.de> wrote:

> Hello everyone,
> 
> Nova-cells filter has been merged now, so I'd like to make use of them
> and set up an installation for a proof of concept.
> 
> My goal is to create new filters and then spawn instances in a demo.

Awesome.  I'd be happy to assist you here with your current (and future) questions.

> 
> Setup:
> - Global: Horizon, Keystone, Glance
> - API cell: nova-api, nova-conductor, nova-cells, nova-network (flat),
> mysql, rabbitmq
> - child cells: nova-cells, nova-conductor, nova-cert, nova-scheduler,
> nova-compute-qemu; cinder-*, mysql, rabbitmq

There's a number of limitations with cells right now, and the above won't *quite* work… but close.  The only issue that I see above is with cinder and nova-network.  Further info below.

> 
> 1. Is the above all services I need to spawn instances from Horizon
> without errors?

Generally, yes.. those are the correct services in the correct cells… *except* nova-network *might* work, but it would have to be in each child cell and you'd need different IP blocks configured in each nova-network in order to work.  They can all be the same layer 2 network, however.  The limitation is because compute needs to talk to nova-network via RPC in order to assign IP addresses…  and RPC communication between nova-compute and other services is intra-cell only.  And if you tried to configure the same /24 in 2 different child cells, since they are separate DBs, you'll get the same IPs handed out in multiple child cells.  More below under #3.

> 
> 2. Do I need cinder-* (or nova-volume)? Is it really optional now?

No, you do not need them if you use local storage for your VMs.  In fact, cinder does not currently work with cells.  I have a patch for this that I need to clean up and submit.

> 
> 3. Do I need nova-network (or quantum-*)? I know quantum-* does not have to run when spawning instances, but I guess I need it to create a
> network for a tenant in the first place!?

Quantum is a better choice vs nova-network with or without cells...as nova-network will be deprecated some day (AFAIK).  If you choose Quantum, you can set this up as a global service to use with cells as long as all of your child cells are on the same layer 2 network.  IP address assignments would be managed globally, etc.  If you choose quantum and set it up globally, the API (nova-api) extensions for networking should work.  In the future, we'll need to find a good way to allow Quantum to work with a config such that different cells can be on different layer 2 networks.

Hope that helps so far,

- Chris