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Azure Spot VM Billing, Pricing, and Eviction Behaviour

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 When adopting Azure Spot Virtual Machines, one of the first challenges is understanding how billing and eviction actually work. Many people initially believe Spot VMs require a minimum runtime, such as 5 minutes. This is not correct. Spot VMs follow the same billing model as standard Pay-As-You-Go VMs: they are billed per second, with a 60-second minimum charge. If a VM runs for less than a minute, you pay for the full minute. After that, you pay only for the exact seconds it runs. The 5-minute intervals you may see on Azure pricing pages are only part of the UI graphs—they are not related to billing.

Spot pricing is based on Azure’s unused capacity. Because of this, Spot VMs often come at massive discounts—sometimes 65% to 90% off On-Demand pricing. The exact discount varies by VM family, region, availability zone, and overall demand. When provisioning a Spot VM, you can set a max price bid. Setting it to “-1” means you agree to pay up to the normal On-Demand price. Your VM will run as long as the current Spot price is equal to or below your bid. If the Spot price moves above your maximum, Azure evicts the VM. Capacity pressure can also trigger eviction, because Azure will always prioritize paying, On-Demand customers.


A critical point is that Spot VMs come with no SLA. Eviction may happen at any time. Standalone Spot VMs usually receive about 30 seconds' notice before eviction. In Virtual Machine Scale Sets, you may wait up to 2 minutes, depending on the configuration. Because of this, Spot is suited only for workloads that tolerate interruptions, such as batch processing, CI/CD agents, media rendering, GenAI model fine-tuning, big data ETL, or dev/test environments. These types of workloads must support checkpointing or quick restarts.
For workloads that must finish, it is best to use Spot as part of a resiliency strategy. A common design is to use VM Scale Sets with Spot Priority Mix mode, where Spot instances run first to save on costs and, if they are evicted, the system automatically fails over to On-Demand VMs. Another option is Azure Batch or Azure Container Instances, which can dynamically choose between Spot and On-Demand based on capacity.
Monitoring Spot's behavior is also important. You can track prices with Azure Monitor, the Pricing Calculator, or automation scripts. In regions with low contention, eviction rates may be extremely small—sometimes below 1%—which brings very high savings with low risk. Combining Spot with Capacity Reservations, Cost Management forecasting, and a solid retry/checkpoint strategy allows you to maximize both reliability and cost efficiency.
Azure Spot VMs are a strong tool for reducing cloud costs, but they require planning. When used correctly, they can deliver exceptional savings while still supporting demanding workloads.

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