libvirt users - Apr 2023 - storage backup with encryption on-the-fly ?

On 06/04/2023 16:12, Peter Krempa wrote:
> On Thu, Apr 06, 2023 at 15:22:10 +0200, lejeczek wrote:
>> Hi guys.
>>
>> Is there a solution, perhaps a function of libvirt, to backup
guest's
>> storage and encrypt the resulting image file?
>> On-the-fly ideally.
>> If not ready/built-in solution then perhaps a best technique you
>> recommend/use?
>> I currently use 'backup-begin' on qcow2s, which are LUKS
encrypted.
> libvirt's block code supports the raw+luks and qcow2+luks encrypted
> image formats with qemu. You should be able to use both for backups too:
>
>
>   <domainbackup mode='push'>
>     <disks>
>       <disk name='vda' type='file'>
>         <driver type='qcow2'/>
>         <target
file='/tmp/backup-test-images/backup-vda.qcow2'>
>           <encryption format='luks'>
>             <secret type='passphrase'
uuid='d5c7780c-80c4-45eb-bee9-9fbbc1f3847c'/>
>           </encryption>
>         </target>
>       </disk>
>   </domainbackup>
>
> Another option would be to use an encrypted device-mapper device via the
> block backend.
>
> Lastly if you need any other storage format the 'pull' mode of
backups
> exposes a (optionally TLS-encrypted) NBD socket from where a client
> application can pull the blocks for backup and store them in any way it
> wants.
>
That works as I hoped, nice & smooth, I've not had the right 
xml syntax.
Are there any docs with more details on the other two 
alternatives?
many thanks, L.

On Fri, Apr 07, 2023 at 19:42:11 +0200, lejeczek wrote:
> 
> 
> On 06/04/2023 16:12, Peter Krempa wrote:
> > On Thu, Apr 06, 2023 at 15:22:10 +0200, lejeczek wrote:
> > > Hi guys.
> > > 
> > > Is there a solution, perhaps a function of libvirt, to backup
guest's
> > > storage and encrypt the resulting image file?
> > > On-the-fly ideally.
> > > If not ready/built-in solution then perhaps a best technique you
> > > recommend/use?
> > > I currently use 'backup-begin' on qcow2s, which are LUKS
encrypted.
> > libvirt's block code supports the raw+luks and qcow2+luks
encrypted
> > image formats with qemu. You should be able to use both for backups
too:
> > 
> > 
> >   <domainbackup mode='push'>
> >     <disks>
> >       <disk name='vda' type='file'>
> >         <driver type='qcow2'/>
> >         <target
file='/tmp/backup-test-images/backup-vda.qcow2'>
> >           <encryption format='luks'>
> >             <secret type='passphrase'
uuid='d5c7780c-80c4-45eb-bee9-9fbbc1f3847c'/>
> >           </encryption>
> >         </target>
> >       </disk>
> >   </domainbackup>
> > 
> > Another option would be to use an encrypted device-mapper device via
the
> > block backend.
> > 
> > Lastly if you need any other storage format the 'pull' mode of
backups
> > exposes a (optionally TLS-encrypted) NBD socket from where a client
> > application can pull the blocks for backup and store them in any way
it
> > wants.
> > 
> That works as I hoped, nice & smooth, I've not had the right xml
syntax.
> Are there any docs with more details on the other two alternatives?
> many thanks, L.
Well, the backup to a (externally provided) device mapper target is
quite straihtforward:

 <domainbackup mode='push'>
   <disks>
     <disk name='vda' type='block'>
       <driver type='qcow2'/>
       <target dev='/dev/mapper/crypt-backup-target'/>
     </disk>
 </domainbackup>

The pull-mode backup with NBD where you handle the encryption in the
client program (not provided by libvirt, but you can have a look at e.g
https://www.libvirt.org/apps.html#backup or oVirt which both implement a
NBD backup flow). To setup a backup in pull mode, simply use:

 <domainbackup mode='pull'>
   <server transport='tcp' name='localhost'
port='1234'/>
   <disks>
     <disk name='vda' type='file'>
       <scratch file='/tmp/backup-sctratch-vda'/>
     </disk>
   </disks>
 </domainbackup>

To setup TLS to encrypt the transport you can use tls='on' and need to
setup the TLS certs. Have a look at the docs for 'server':

 https://www.libvirt.org/formatbackup.html