Re: Updating domains definitions via API

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On Fri, 13 May 2022 at 00:17, Darragh Bailey <daragh.bailey@xxxxxxxxx> wrote:

On Thu 12 May 2022, 21:34 Laine Stump, <laine@xxxxxxxxxx> wrote:
The virDomainDefineXMLFlags API (and also the older/deprecated
virDomainDefineXML API) doesn't require that the domain first be
undefined (with one notable exception - see below[*]). If you define a
domain that already exists with the same name and uuid, then the effect
is to "redefine" (or "update" if you prefer) the existing domain of that
name. If the domain is currently active, then the changes will take
effect the next time the domain is shut down ("Destroy"ed in libvirt API
parlance) and re-started.

Unfortunately trying to call this via ruby-libvirt doesn't appear to behave as expected. It appears that if I add an nvram element without a loader element to the os block, the following code block will execute without issue but also without changing the domain XML:

# Apply XML changes directly
if descr_changed
    env[:ui].info("Updating domain definition due to configuration change")
    new_descr =
    xml_descr.write new_descr
    # env[:machine].provider.driver.connection.client provides access to the ruby-libvirt connection object
    libvirt_domain = env[:machine].provider.driver.connection.client.define_domain_xml(new_descr, 1)
    domain = env[:machine].provider.driver.connection.servers.get(env[:machine].id.to_s)
  rescue Fog::Errors::Error => e
    raise Errors::UpdateServerError, error_message: e.message

I've by-passing the fog-libvirt to call the ruby-libvirt connection object directly to try and avoid any unexpected interference when testing the API call out e.g.

So not only is there no exception thrown if the XML change is ignored, I've noticed there doesn't appear to be an easy way to check using the API either, in that doesn't indicate that the domain has been updated whether I call it on the libvirt_domain object returned, or an instance from before the define_domain_xml call is made.

It appears that the only way is to perform a call to get the xml definition of the libvirt_domain object returned in the above block and see if that matches the xml that was sent, if not, error.

Is this the expected usage of the API? Or should the call to define_domain_xml raise an exception if it cannot update the domain XML? as opposed to a schema validation error which does appear to be detected when I did something stupid.


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