Spec Lite: Add new container format




Compression method using hardware to accelerate has already been implemented in cinder project. A new container format ‘compressed’ needs to be added to container format list in glance to support this.


A new container format ‘compressed’ option needs to be added to the default container_format configuration list.


New container format option


If users chose to upload volume using compression method, cinder will do compression and then upload to glance. The uploaded image’s metadata will be ‘compressed’ in container_format so that it can be correctly processed after downloaded. Volume disk_format will not be changed by this compression process.

  • Glance will not handle the compression and decompression progress, which means glance will not check if it is a vaild compressed image. Whoever is to upload or download the image is responsible for compression or decompression.

  • Uploaded image will not be automatically compressed if simply changing the container_format as ‘compressed’. Compression or decompression happens when image is uploading from volume or downloading to a volume.

  • Glance will not identify what format the compressed image really is. In glance’s view, it is just a blob. Image consumer (such as cinder) will identify the real format such as gzip, rar or other format.

other impact:

Nova cannot currently handle images in a compressed container format. We propose patching Nova to reject such images: https://review.opendev.org/#/c/673407/


Include in train release