What is Instance Boot Source?

When creating a new instance via the dashboard you are asked to select an Instance Boot Source. This is the template used to create an instance. You can use a snapshot of an existing instance, an image, or a volume (if enabled). You can also choose to use persistent storage by creating a new volume.

Lets clarify these terms.

Images

These are pre-configured operating system images that are available for selection as a boot source. Images are provided by the OpenStack service known as Glance. When booting from an image you can elect to create a new volume from the image. If you choose to create a new volume you need to decide if you want to the volume deleted on instance termination.

Volumes

Volumes are block devices provided by the Cinder service that can be attached to instances. Volumes can be used as a boot source provided they contain an appropriate operating system.

Instance Snapshot

Instances that have been snapshotted can be selected as a boot source. Instance snapshots are Images of the type “Snapshot”.

Volume Snapshot

Volumes that have been snapshotted can be selected as a boot source.

Ephemeral vs Persistent

Ephemeral storage is only available for the lifetime of the instance so when the instance is terminated, any data that was stored on it is lost. It is stored in the same block storage as persistent data to allow instances to retain their ephemeral storage if the instance is live migrated to another physical hypervisor.

Persistent storage on the other hand will persist when instances are rebooted.

Select the boot source

Boot Source Description Type
Image, do not create new volume This option allows a user to specify an image from the Glance repository to copy into an ephemeral disk. Ephemeral
Image, create new volume, do not delete volume on terminate This option allows a user to specify an image from the Glance repository to copy into a persistent volume. Persistent
Image, create new volume, delete volume on terminate This option allows a user to specify an image from the Glance repository to copy into a volume which will be deleted on termination. Ephemeral
Instance Snapshot This option allows a user to specify an instance snapshot to use as the root disk; the disk is ephemeral. Ephemeral
Volume, do not delete on terminate This option allows a user to specify a Cinder volume (by name or UUID) that should be directly attached to the instance as the root disk; any content stored in volume will persist on instance termination. Persistent
Volume, delete on terminate This option allows a user to specify a Cinder volume (by name or UUID) that should be directly attached to the instance as the root disk; the volume will be deleted on termination. Ephemeral
Volume Snapshot, do not delete on terminate This option allows a user to specify a Cinder volume snapshot (by name or UUID) that should be directly attached to the instance as the root disk; the volume will persist on instance termination. Persistent
Volume Snapshot, delete on terminate This option allows a user to specify a Cinder volume snapshot (by name or UUID) that should be directly attached to the instance as the root disk; the volume will be deleted on termination. Ephemeral