Cloud OS images from Ubuntu, Fedora, Centos and most other Linux distributions have their password authentication disabled by default. So, every time when creating a VM instance on OpenStack with a Heat template, I have been using user_data directive to set the default password, without really understanding what’s going on inside.
Nova adapts ephemeral storage for VMs by default. The ephemeral storage resides on the local hard disks of the host computes and present a virtual disk for each VM. These virtual disks are created at the time of the VM creation, and are deleted with the VM, so are called ephemeral. If the host machine crashes, you lose the VM with all its data stored in disk.
