Spec Lite: Add location url prefix attribute to each store




In multiple store implementation, glance has added new metadata ‘store’ to location object, so that it will be easy to identify the store that particular image is uploaded. When operator upgrades glance node to use multiple stores, then existing images does not have store information associated with it. So if user wants to download any such particular image, then as it does not have ‘store’ associated with it, the said image will be searched in all the configured stores. This may cause the performance overhead.


To overcome this, we propose to add new attribute ‘_url_prefix’ to each of the store object. When glance-api service starts it stores a global map in the memory which includes store object, scheme and location_class for each of the store.

Sample of location map stored in the memory:

    'file_2': {
        'store': <glance_store._drivers.filesystem.Store object>,
        'store_entry': 'file',
        'location_class': <class 'glance_store._drivers.filesystem.StoreLocation'>
    'file_1': {
        'store': <glance_store._drivers.filesystem.Store>,
        'store_entry': 'file',
        'location_class': <class 'glance_store._drivers.filesystem.StoreLocation'>

At the time of initialization of each store, a location url will be retrieved using each stores configuration and assigned to ‘_url_prefix’ attribute of each store object. Whenever any GET call to image (before upgrading to multiple stores) is made, the location url of that image will be matched with ‘_url_prefix’ and equivalent store information will be updated to that image’s location metadata.


None, carry on using current mechanism.

impacts: DocImpact


Include in Train release.