Resource tracking

Resource tracking

Cinderlib users will surely have their own variables to keep track of the Backends, Volumes, Snapshots, and Connections, but there may be cases where this is not enough, be it because we are in a place in our code where we don’t have access to the original variables, because we want to iterate all instances, or maybe we are running some manual tests and we have lost the reference to a resource.

For these cases we can use cinderlib’s various tracking systems to access the resources. These tracking systems are also used by cinderlib in the serialization process. They all used to be in memory, but some will now reside in the metadata persistence storage.

Cinderlib keeps track of all:

  • Initialized Backends.

  • Existing volumes in a Backend.

  • Connections to a volume.

  • Local attachment to a volume.

  • Snapshots for a given volume.

Initialized Backends are stored in a dictionary in Backends.backends using the volume_backend_name as key.

Existing volumes in a Backend are stored in the persistence storage, and can be lazy loaded using the Backend instance’s volumes property.

Existing Snapshots for a Volume are stored in the persistence storage, and can be lazy loaded using the Volume instance’s snapshots property.

Connections to a Volume are stored in the persistence storage, and can be lazy loaded using the Volume instance’s connections property.

Note

Lazy loadable properties will only load the value the first time we access them. Successive accesses will just return the cached value. To retrieve latest values for them as well as for the instance we can use the refresh method.

The local attachment Connection of a volume is stored in the Volume instance’s local_attach attribute and is stored in memory, so unloading the library will lose this information.

We can easily use all these properties to display the status of all the resources we’ve created:

# If volumes lazy loadable property was already loaded, refresh it
lvm_backend.refresh()

for vol in lvm_backend.volumes:
    print('Volume %s is currently %s' % (vol.id, vol.status)

    # Refresh volume's snapshots and connections if previously lazy loaded
    vol.refresh()

    for snap in vol.snapshots:
        print('Snapshot %s for volume %s is currently %s' %
              (snap.id, snap.volume.id, snap.status))

    for conn in vol.connections:
        print('Connection from %s with ip %s to volume %s is %s' %
              (conn.connector_info['host'], conn.connector_info['ip'],
               conn.volume.id, conn.status))
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