A virtual machine image is a single file which contains a virtual disk that has a bootable operating system. The images operating system will be installed on the VM upon its creation. The user can create many VMs utilising the same image.
Glance is the Image Service in OpenStack. Trough glance, users can upload, discover and manage images. When the image is uploaded to Glance, it will become available to the project as a bootable image.
The disk formats supported by Glance are
- Raw (Unstructured disk format)
- qcow2 (QEMU image format, native for KVM and QEMU)
- AMI; ARI; AKI
City Cloud recommends the usage of images packaged in Raw for regions running Ceph and qcow2 for non-Ceph regions. Please note that some regions may run Ceph backend for volumes.
Images for different OS distributions are available in City Cloud.
In City Control Panel, during creation of servers, a boot source should be selected. The options provided are public images, private images and snapshot (Figure 1).
Figure 1. Creation of Server - Boot Source
- Public images are pre-loaded images available for all projects and maintained by City Cloud. Images are uploaded upon OS release and removed when version comes to end-of-life. Images can be chosen per OS (Ubuntu, CentOS, Debian, CoreOS, Fedora, Suse, freebsd or Windows) as shown in Figure 2.
- Private images are customs images provided by the user and available to a specific project.
- Snapshot is an image from another VM or volume available in the same project. This option is also provided by the user upon creation of new server.
Figure 2. Creation of Server - Public Image OS options