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Glance image to base image mapping ?

asked 2015-07-28 01:15:35 -0500

Vinu gravatar image

Would like to know where exactly is the mapping done between the images uploaded to Glance and the corresponding image file that is downloaded to compute nodes under "/var/lib/nova/images/_base" when nova boot <> is used to instantiate a VM. I could see that under _base dir, there is a raw disk file getting created with HEX # as file names. And this image is used as base line image for all the new VM instances.

The info that I'm looking for is, how the the glance uploaded image and this _base image's are mapped when ever a new nova VM in launched so that only the first time the _base/ image is downloaded and later on its reused.

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answered 2018-09-18 01:14:16 -0500

according to the source code, base image name is the sha1 of its image_id:

nova/virt/libvirt/imagecache.py

def get_cache_fname(images, key):
    image_id = str(images[key])
    if ((not CONF.libvirt.remove_unused_kernels and
         key in ['kernel_id', 'ramdisk_id'])):
        return image_id
    else:
        return hashlib.sha1(image_id).hexdigest()
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Asked: 2015-07-28 01:15:35 -0500

Seen: 185 times

Last updated: Jul 28 '15