Should Low‑Traffic Workloads Use Boot‑From‑Image or Boot‑From‑Volume in OpenStack?

For a low‑traffic workload the operator wants to minimize monthly expenses while retaining the ability to snapshot and recover instances. The decision hinges on whether to boot instances from the local ephemeral disk (boot‑from‑image) or from a Cinder volume (boot‑from‑volume). Boot‑from‑image avoids per‑GB volume charges and network attachment overhead, but it consumes compute‑node storage that is not limited by Nova’s ram_allocation_ratio or cpu_allocation_ratio, requiring separate monitoring of host disk usage to prevent out‑of‑space failures.

Boot‑from‑volume shifts the cost to Cinder storage and introduces additional network traffic, yet provides easy snapshotting and volume‑based mobility. Using a lower‑performance Cinder backend or disabling volume backups can cut expenses, but the effect on durability and restore time for infrequently accessed data is unclear.

• How does ephemeral‑disk consumption influence Nova scheduler placement when ram_allocation_ratio and cpu_allocation_ratio are adjusted?
• What level of cost saving is achievable by disabling Cinder backups or switching to a reduced‑replication backend for boot‑from‑volume instances?
• Can the reduced durability of a low‑cost Cinder backend be tolerated for workloads that experience only occasional read/write traffic?