Open Stack

+1 on Chris comments on implementation and API.
Migrate, if all is ideal, should take the initial launch flavor.

-----Original Message-----
From: Chris Friesen [mailto:chris.friesen at windriver.com] 
Sent: Thursday, November 05, 2015 8:46 PM
To: openstack-dev at lists.openstack.org
Subject: Re: [openstack-dev] [Nova] Migration state machine proposal.

On 11/05/2015 08:33 AM, Andrew Laski wrote:
> On 11/05/15 at 01:28pm, Murray, Paul (HP Cloud) wrote:

>> Or more specifically, the migrate and resize API actions both call 
>> the resize function in the compute api. As Ed said, they are 
>> basically the same behind the scenes. (But the API difference is 
>> important.)
>
> Can you be a little more specific on what API difference is important to you?
> There are two differences currently between migrate and resize in the API:
>
> 1. There is a different policy check, but this only really protects the next bit.
>
> 2. Resize passes in a new flavor and migration does not.
>
> Both actions result in an instance being scheduled to a new host.  If 
> they were consolidated into a single action with a policy check to 
> enforce that users specified a new flavor and admins could leave that 
> off would that be problematic for you?


To me, the fact that resize and cold migration share the same implementation is just that, an implementation detail.

 From the outside they are different things...one is "take this instance and move it somewhere else", and the other "take this instance and change its resource profile".

To me, the external API would make more sense as:

1) resize

2) migrate (with option of cold or live, and with option to specify a destination, and with option to override the scheduler if the specified destination doesn't pass filters)


And while we're talking, I don't understand why "allow_resize_to_same_host" 
defaults to False.  The comments in https://bugs.launchpad.net/nova/+bug/1251266
say that it's not intended to be used in production, but doesn't give a rationale for that statement.  If you're using local storage and you just want to add some more CPUs/RAM to the instance, wouldn't it be beneficial to avoid the need to copy the rootfs?

Chris

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