On 01/23/2012 11:01 PM, Ayal Baron wrote:
----- Original Message -----
----- Original Message -----
From: "Ayal Baron"<[email protected]>
To: "Itamar Heim"<[email protected]>
Cc: [email protected], "Miki Kenneth"<[email protected]>
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"<[email protected]>
To: "Ayal Baron"<[email protected]>
Cc: [email protected]
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.
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