A cloud compute instance offered at 50-90% discount vs on-demand pricing — but the provider can reclaim it with little notice (typically 2 minutes) when capacity is needed elsewhere.
Spot Instances (AWS), Preemptible VMs (GCP), and Spot VMs (Azure) sell otherwise-unused cloud capacity at deep discount. The catch: the cloud can take the instance back any time, terminating workloads. Spot is right for: batch jobs (rerun cheaply), stateless workers behind a queue (other workers pick up the slack), CI/CD runners (rebuild on terminate), distributed training (checkpoint and resume). Wrong for: stateful databases, long-running stateful services, anything that can't tolerate interruption.
Running a 200-node ML training cluster on Spot Instances — 75% lower cost than On-Demand, with periodic checkpointing to handle reclamations.
Spot Instances are the single largest cloud cost lever for workloads that tolerate interruption — savings often dwarf any other optimization technique.
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