[Engine-devel] ovirt core MOM

[Itamar Heim]

On 02/01/2012 02:16 PM, Miki Kenneth wrote:
>
>
> ----- Original Message -----
>> From: "Ayal Baron"<abaron at redhat.com>
>> To: "Itamar Heim"<iheim at redhat.com>
>> Cc: "Miki Kenneth"<mkenneth at redhat.com>, engine-devel at ovirt.org
>> Sent: Wednesday, February 1, 2012 12:26:12 PM
>> Subject: Re: [Engine-devel] ovirt core MOM
>>
>>
>>
>> ----- Original Message -----
>>>
>>>
>>> ----- Original Message -----
>>>> From: "Ayal Baron"<abaron at redhat.com>
>>>> To: "Itamar Heim"<iheim at redhat.com>
>>>> Cc: "Miki Kenneth"<mkenneth at redhat.com>, engine-devel at ovirt.org
>>>> Sent: Wednesday, February 1, 2012 11:41:43 AM
>>>> Subject: Re: [Engine-devel] ovirt core MOM
>>>>
>>>>
>>>>
>>>> ----- Original Message -----
>>>>> On 01/23/2012 11:01 PM, Ayal Baron wrote:
>>>>>>
>>>>>>
>>>>>> ----- Original Message -----
>>>>>>>
>>>>>>>
>>>>>>> ----- Original Message -----
>>>>>>>> From: "Ayal Baron"<abaron at redhat.com>
>>>>>>>> To: "Itamar Heim"<iheim at redhat.com>
>>>>>>>> Cc: engine-devel at ovirt.org, "Miki
>>>>>>>> Kenneth"<mkenneth at redhat.com>
>>>>>>>> Sent: Sunday, January 22, 2012 11:19:03 AM
>>>>>>>> Subject: Re: [Engine-devel] ovirt core MOM
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> ----- Original Message -----
>>>>>>>>> On 01/20/2012 11:42 PM, Miki Kenneth wrote:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> ----- Original Message -----
>>>>>>>>>>> From: "Itamar Heim"<iheim at redhat.com>
>>>>>>>>>>> To: "Ayal Baron"<abaron at redhat.com>
>>>>>>>>>>> Cc: engine-devel at ovirt.org
>>>>>>>>>>> Sent: Friday, January 20, 2012 2:12:27 AM
>>>>>>>>>>> Subject: Re: [Engine-devel] ovirt core MOM
>>>>>>>>>>>
>>>>>>>>>>> On 01/19/2012 11:58 AM, Ayal Baron wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> ----- Original Message -----
>>>>>>>>>>>>> On 01/18/2012 05:53 PM, Livnat Peer wrote:
>>>>>>>>>>>>>> Hi All,
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> This is what we've discussed in the meeting today:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Multiple storage domain:
>>>>>>>>>>>>>> - Should have a single generic verb for removing a
>>>>>>>>>>>>>> disk.
>>>>>>>>>>>>>> - We block removing the last template disk - template
>>>>>>>>>>>>>> is
>>>>>>>>>>>>>> immutable.
>>>>>>>>>>>>>
>>>>>>>>>>>>> but it will be deleted when deleting the template,
>>>>>>>>>>>>> right?
>>>>>>>>>>>>
>>>>>>>>>>>> Of course.
>>>>>>>>>>>> The point is that the template is an immutable object
>>>>>>>>>>>> and
>>>>>>>>>>>> should
>>>>>>>>>>>> not change (until we support editing a template at
>>>>>>>>>>>> which
>>>>>>>>>>>> point
>>>>>>>>>>>> the
>>>>>>>>>>>> user would have to change the template to edit mode
>>>>>>>>>>>> before
>>>>>>>>>>>> being
>>>>>>>>>>>> able to make such changes and maybe also be able to run
>>>>>>>>>>>> it
>>>>>>>>>>>> and
>>>>>>>>>>>> make changes internally?).
>>>>>>>>>>>
>>>>>>>>>>> When i hear "edit a template" i don't expect replacing
>>>>>>>>>>> the
>>>>>>>>>>> files.
>>>>>>>>>>> I expect a new edition of disks appearing as a new
>>>>>>>>>>> version
>>>>>>>>>>> of
>>>>>>>>>>> the
>>>>>>>>>>> template. but they don't have to derive from same
>>>>>>>>>>> original
>>>>>>>>>>> template.
>>>>>>>>>>> say i want to create a "Fedora 16 template", then update
>>>>>>>>>>> it
>>>>>>>>>>> every
>>>>>>>>>>> month
>>>>>>>>>>> with latest "yum update".
>>>>>>>>>>> it doesn't matter if i use a VM from same template or
>>>>>>>>>>> just
>>>>>>>>>>> create
>>>>>>>>>>> a
>>>>>>>>>>> new one.
>>>>>>>>>>> then specify it is V2 of the "Fedora 16 template".
>>>>>>>>>>> when someone creates a VM from this template, default
>>>>>>>>>>> version
>>>>>>>>>>> would
>>>>>>>>>>> be
>>>>>>>>>>> latest (but we can let them choose specific older
>>>>>>>>>>> versions
>>>>>>>>>>> as
>>>>>>>>>>> well)
>>>>>>>>>> +1. Nicely put.
>>>>>>>>>> And just to add another common use case is the pool
>>>>>>>>>> usage.
>>>>>>>>>> When we creating stateless VM pool from the template,
>>>>>>>>>> it would be nice to be able to update the template to V2,
>>>>>>>>>> and have all the newly created VMs dynamically based to
>>>>>>>>>> the
>>>>>>>>>> new
>>>>>>>>>> template.
>>>>>>>>>
>>>>>>>>> that is indeed where i was going with it as well, but not
>>>>>>>>> as
>>>>>>>>> trivial,
>>>>>>>>> since need to wait for VMs to stop and return to pool and
>>>>>>>>> create
>>>>>>>>> new
>>>>>>>>> ones and remove old ones.
>>>>>>>>> also, creating new ones may involve an admin action of
>>>>>>>>> first
>>>>>>>>> boot
>>>>>>>>> +
>>>>>>>>> take
>>>>>>>>> of first snapshot
>>>>>>>>>
>>>>>>>>> (hence i stopped the previous description before this
>>>>>>>>> part,
>>>>>>>>> but
>>>>>>>>> since
>>>>>>>>> you opened the door...)
>>>>>>>>
>>>>>>>> Yes, but this all goes to template versioning (which is
>>>>>>>> great
>>>>>>>> and
>>>>>>>> we
>>>>>>>> need).
>>>>>>>> For the user though, creating a new template version like
>>>>>>>> you
>>>>>>>> described would be a long and wasteful process, and is not
>>>>>>>> what
>>>>>>>> I'm
>>>>>>>> talking about.
>>>>>>>>
>>>>>>>> Unless we support nested templates (second template would
>>>>>>>> be
>>>>>>>> a
>>>>>>>> snapshot over the first one), then we're likely to require
>>>>>>>> way
>>>>>>>> too
>>>>>>>> much space and creation process would be too slow (having
>>>>>>>> to
>>>>>>>> copy
>>>>>>>> over all the bits).
>>>>>>>> I think the pool example is an excellent example where I
>>>>>>>> would
>>>>>>>> not
>>>>>>>> want to have 2 copies of the template where the only
>>>>>>>> difference
>>>>>>>> between them is a set of security patches I've applied to
>>>>>>>> the
>>>>>>>> new
>>>>>>>> template.
>>>>>>> Not sure I understand how you do that while vms are still
>>>>>>> running
>>>>>>> on
>>>>>>> the original template?
>>>>>>
>>>>>> They either:
>>>>>> 1. wouldn't be (if changes are in place)
>>>>>> 2. if we support template over template (from snapshot) then
>>>>>> no
>>>>>> issue at all.
>>>>>>      Once all VMs stop running on previous template we can
>>>>>>      live
>>>>>>      merge the 2.
>>>>>>
>>>>>>>>
>>>>>>>> So the 2 options are for what I'm suggesting are:
>>>>>>>> 1. decommission the old template by making in place changes
>>>>>>>> 2. support template snapshots
>>>>>>> Not sure how this will work and what use case it serves?
>>>>>>
>>>>>> number 1: changing the template for stateless pools.
>>>>>> number 2: for anything you want including template
>>>>>> versioning.
>>>>>> Template versioning should have 2 flavours:
>>>>>> 1. my golden image is outdated and I would like to
>>>>>> decommission
>>>>>> it
>>>>>> and replace with a new one created from scratch (i.e. same
>>>>>> name,
>>>>>> new VMs would be derived from new template, no data dedup).
>>>>>> 2. my golden image is outdated and I would like to update it
>>>>>> internally - create a VM from it, make the changes, seal this
>>>>>> VM
>>>>>> as the new version of the template (not using the process we
>>>>>> have
>>>>>> today which copies all the data, just change it to be
>>>>>> immutable).
>>>>>>
>>>>>> The latter requires supporting trees.
>>>>>
>>>>> use case wise, #1 is easier, and covers both use cases - it
>>>>> only
>>>>> varies
>>>>> in amount of IO/Space, so when someone tackles this
>>>>> implementation
>>>>> wise,
>>>>> I'd vote for doing #1 first.
>>>>>
>>>> No, it varies in amount of time and complexity for user.
>>>> It might also be quite complex to create the same image again.
>>>> To this I can only say 'provisioning provisioning provisioning'.
>>>> The point is to make the user's life easier and making
>>>> provisioning
>>>> a
>>>> breeze, forcing #1 is going in the opposite direction.
>>>>
>>>>
>>>
>>> #2 does not solve #1.
>>> #2 allows doing part of #1 in a more efficient way.
>>> so there is no reason to not do #1.
>>> (there is also no reason to not do #2)
>>>
>>
>> I agree, that is why I said template versioning should have both.
> Decision?

decision about what? this is a theoretical discussion until someone will 
actively work on the template versioning feature.
both modes should be supported. which one first would probably depend on 
the priorities of the one sending the patches.