qcow2 images on Nimbus/Alamo

Support for the qcow2 virtual machine image format has been added to Nimbus on Alamo.  One feature of qcow2 is that the size of an image on disk grows only as data is added to it. This is in contrast to a raw image file that is of a fixed size (the size of the virtual disk) which we typically gzip to reduce storage space.

One of the benefits of using qcow2 images is that Nimbus does not have to perform a gzip or gunzip step when running and saving virtual machines. This reduces the time to start and save virtual machines significantly.   We will be adding qcow2 images for Linux distributions over time. If you wish to use specific distributions/versions, please let us know.   An important note is that the qcow2 images provided by some distributions (e.g. Ubuntu, Fedora), don't work well out of the box with Nimbus. The reason for this is that while Nimbus adds your ssh key to the root account of the virtual machine, these images do not allow direct login to the root account (they expect you to log in to a normal user account such as ubuntu or ec2-user and then use sudo).