9:36 a.m.
On 11/02/2014 11:04 PM, Crístian Viana wrote:
Hi everyone,
I'm presenting here my proposal for the feature "Domain snapshots"
which is expected to be implemented for Kimchi 1.4.
Description
A domain snapshot is a "moment in time" of a domain. After a snapshot
is created, a domain can be reverted to that snapshot (i.e. reverted
to the exact same state it was when the snapshot was created). If a
snapshot is created while the domain is stopped, only its disks will
be used in that snapshot; otherwise, its memory state will also be used.
A snapshot can be created on top of another snapshot, which makes it
possible to have a tree-like snapshot structure for each domain. When
a snapshot is created, the last snapshot used in that domain execution
will be its parent. If there are no previous snapshot in that
execution, the new snapshot will have no parent.
Existing functions which also deal with snapshots will be updated.
REST API
Create a domain snapshot
Syntax
POST /vms//<vm-name>//snapshots
Parameters
name: The snapshot name (optional). If omitted, a default name will be
used.
Return
An asynchronous Task with "target_uri" containing
"/vms/</vm-name/>/snapshots//<new-snapshot-name>/". As expected
with
any Task, the process can be tracked by checking the corresponding
task's status.
Look up one domain snapshot
Syntax
GET /vms//<vm-name>//snapshots//<snapshot-name>/
Parameters
None.
Return
A snapshot structure with the following properties:
name: The snapshot name.
state: The corresponding domain state when the snapshot was created.
created: The time when the snapshot was created (in seconds, since the
epoch).
parent: The name of the parent snapshot, or an empty string if there
is no parent.
Look up multiple domain snapshosts
Syntax
GET /vms//<vm-name>//snapshots
Parameters
parent: The name of the parent snapshot of the requested snapshots
(optional). If omitted, only the "root" snapshots for that domain will
be returned.
Return
A list of the structures returned by the action "Look up one domain
snapshot". All snapshots returned by this call will have "parent" as
their parents.
Update a domain snapshot
Syntax
PUT /vms//<vm-name>//snapshots//<snapshot-name>/
Parameters:
name: The new snapshot name.
Return:
The structure returned by the action "Look up one domain snapshot"
with the updated values.
We can postpone it.
I think the most important operations are: create, delete and revert a
snapshot. When we have those 3 operations done we can work on update.
Delete a domain snapshot
Syntax
DELETE /vms//<vm-name>//snapshots//<snapshot-name>/
Parameters
None.
Return
None.
Revert to a domain snapshot
Syntax
POST /vms//<vm-name>//snapshots//<snapshot-name>//revert
Parameters
None.
Return
None.
CHANGE: List the current snapshot in a domain
Syntax
GET /vms//<vm-name>/
Additional parameters
None.
Additional return
current-snapshot: the snapshot name in which the domain execution is
on, or an empty string if there is no current snapshot.
I'd say to use the API /vms/<name>/snaphosts to provide this information.
You can do it by a parameter or using a specific API for it: GET
/vms/<name>/snaphosts/current
CHANGE: Delete snapshots when deleting a domain
Syntax
DELETE /vms//<vm-name>/
Additional parameters
None.
Additional return
None.
CHANGE: Clone snapshots when cloning a domain
Syntax
POST /vms//<vm-name>//clone
Additional parameters
None.
Additional return
None.
Open discussion
1. When creating a snapshot in a running domain, should we try to
minimize the domain's downtime? There's a libvirt flag for that
but it increases the memory dump file size.
As Kimchi can not deal well with paused domains yet, I suggest to use
the libvirt flag to avoid this state.
But of course, we can revert it when we properly support paused state.
"If @flags includes VIR_DOMAIN_SNAPSHOT_CREATE_LIVE, then the domain is
not paused while creating the snapshot. This increases the size of the
memory dump file, but reduces downtime of the guest while taking the
snapshot."
1.
2. When deleting a snapshot, should we keep their children or should
we only delete that snapshot? Keep in mind that snapshots follow a
tree-like structure. This feature is already implemented by
libvirt, it makes no difference for us in the implementation (it's
just a different flag), but we need to think if the user would
expect that the snapshot's children will be deleted as well when
deleting one snapshot.
I'd say to only remove the snapshot itself. But we could provide a check
box to user select or not to remove all its children
In that case we need to accept a parameter on DELETE request
DELETE /vms/<name>/snapshots/<snap> {mode: node|all}
1.
2. The properties returned by the action "Look up one domain
snapshot" are just the ones I thought it might be useful for now.
A snapshot has more properties than that but I'm not sure if we
should just dump everything.
No. We should provide and expose only the information needed by user
otherwise they do not make sense.
1.
2. The property updated by the action "Update a domain snapshot"
(i.e. "name") is the only one I thought it might be relevant.
Other properties can be updated as well if we want to.
I only can think on name as well.
1.
Any feedback is welcome.
Best regards,
Crístian.
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