Glance (Image)

Glance is the OpenStack image service. It stores and distributes VM images that Nova uses when creating virtual machines.

Role in CobaltCore

When a user requests a new VM, Nova asks Glance for the image. Glance retrieves it from its backend store and streams it to the compute node (or serves it via a URL that the hypervisor can fetch directly).

Key concepts

Concept	Description
Image	A VM disk image in a format Nova can boot (qcow2, raw, ISO)
Image store	The backend where image data is persisted (Ceph RBD or Swift)
Image metadata	Properties attached to an image (minimum RAM, disk size, OS type, architecture)

Backend

In CobaltCore, Glance typically uses Ceph RBD as its image store. Images uploaded to Glance are stored as RBD objects, and Nova can use copy-on-write cloning to provision VM disks from Glance images without copying data.

Deployment

Glance is deployed via Helm as part of the OpenStack chart set.

INFO

Detailed configuration documentation (image import workflows, image signing, multi-store configuration) is being added. See the OpenStack Glance docs in the meantime.