8:04 p.m.
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.
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.
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.
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.
3. 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.
4. 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.
Any feedback is welcome.
Best regards,
Crístian.