[Engine-devel] VM Payload feature

[Itamar Heim]

On 02/27/2012 09:14 PM, David Lutterkort wrote:
> On Mon, 2012-02-27 at 18:22 +0200, Itamar Heim wrote:
>> On 02/27/2012 05:45 PM, Dan Kenigsberg wrote:
>>> On Mon, Feb 27, 2012 at 04:19:02PM +0200, Shahar Havivi wrote:
>>>> We encounter a problem with persisting the content to engine database (we don't
>>>> want to save the file the database).
>>>>
>>>> There are some solution for that:
>>>> 1. we do want to persist files to the database (with size limitation).
>>>> 2. engine can expect file path (nfs or http) and persist only the file url
>>>> 3. we can use this feature in run-once only hence no persistence is needed.
>>
>> i think size limitation should be ok.
>
> Yes, this only needs to allow for a small amount of data; EC2 limits it
> to 16k (though they further limit it to 2k in certain circumstances[1])
> Other providers have similar limits. In general, people pass only a few
> hundred bytes in in most cases, so a limit of 16k is plenty.
>
>> looking forward to next phase of supporting the cloud based api for
>> guests which david mentioned earlier in the thread, vm payload should
>> allow passing things like guest keypair files.
>> looking at the API[1] david mentioned, i didn't notice files other than
>> keypair's, but i may have missed them.
>> the rest of the API seems to be based on data that can be retrieved from
>> the DB.
>> David - any more insight as to when/how files are needed?
>
> A good thing to look at is cloud-init; it's a widely used tool for early
> initialization of cloud instances. Yes, by far the most important thing
> it does is retrieve the public key from the meta-data server and stuffs
> it into $USER/.ssh/authroized_keys (USER is either root or sth like
> ec2-user, depending on the image)
>
>> (btw, can you please remind where in the metadata do you pass extra
>> information aelous needs?)
>
> For Aeolus, it passes all the information it needs to talk to its config
> server and pull down additional things as the user-data. The format is
> completely custom, and the cloud platform only needs to make sure that
> the data that's passed in through the API shows up in the instance - it
> should be completely opaque to the oVirt.

can you give a pointer how/where in the EC2 api this would appear under?

>
>>>>
>>>> Thoughts, other ideas?
>>>
>>> Let's re-ask the question about the (Engine) API: Do we need the payload
>>> to be passed on VM definition? Or is it enough to pass it on VM startup?
>>
>> my view is vm definition, not only startup.
>
> For a cloud, you generally want to launch multiple VM's off the same
> image, and therefore need to be able to specify the user data for each
> VM. Whether that happens when you define or launch the VM isn't all that
> important, though it would be a little friendlier to users to do it at
> VM start, since they then do not need to have the user data ready (or
> know it) when they define a VM.

well, true for cloud when image start is also creating the instance, 
while in ovirt, at least for now, you need to create the VM then launch it.
i agree you need to be able to pass this at VM start, but considering VM 
are mostly stateful, i don't see why you wouldn't let user persist this 
like the VM is presistent.

>
> David
>
> [1] https://forums.aws.amazon.com/thread.jspa?threadID=74488
> [2] https://help.ubuntu.com/community/CloudInit
>
>