Fault-Tolerant AKS Workloads Not Using Spot Node Pools

AKS supports Spot node pools backed by Azure Spot Virtual Machine Scale Sets, which use unused Azure capacity at a significant discount but can be evicted when Azure needs the capacity back.

Spot has to be opted into deliberately. A Spot pool can only be a secondary pool, its priority and max price cannot be changed after creation, and AKS applies a NoSchedule taint to Spot nodes, so workloads only land there when teams add a matching toleration and node affinity. Without that step, interruptible work keeps running at full price. The opportunity is limited to workloads that are stateless, retry-safe or checkpointed; anything that needs an SLA should stay on regular nodes.

Regular node pool

Nodes billed at pay-as-you-go VM rates (or covered by reservations or savings plans) for as long as they run

Spot node pool

Nodes billed at variable Spot prices by region and VM size, which Microsoft cites as up to 90% below pay-as-you-go

Spot max price

With -1 nodes are not evicted on price and pay the lower of the current Spot or standard price

Eviction

Spot nodes have no SLA and are removed when Azure needs capacity; with the Delete policy the nodes are deleted

• Run the FinOps toolkit Azure Resource Graph query 'AKS clusters without Spot VMs', which lists agent pools where enableAutoScaling is true and scaleSetPriority is null
• Check Azure Advisor for the AKS cost recommendation 'Consider Spot nodes for workloads that can handle interruptions'
• Inventory workloads on regular pools that are Jobs, CronJobs, CI runners, queue workers or other controllers that can be rescheduled, and exclude StatefulSets and latency-critical services
• Use AKS cost analysis to size the spend on node pools that host those interruption-tolerant workloads

• Add a secondary Spot node pool with az aks nodepool add --priority Spot --eviction-policy Delete --spot-max-price -1 and enable the cluster autoscaler on it, which replaces evicted nodes when capacity returns
• Add a toleration for kubernetes.azure.com/scalesetpriority=spot:NoSchedule and node affinity on the kubernetes.azure.com/scalesetpriority=spot label to the workloads that should move
• Keep a regular node pool available as fallback for capacity shortages, and use a priority expander in the autoscaler so Spot pools are tried first when both can serve a pod
• Make moved workloads eviction-safe with graceful shutdown handling, retries or checkpointing and appropriate PodDisruptionBudgets
• Prefer the Delete eviction policy: nodes left in stopped-deallocated state under the Deallocate policy count against compute quota and can interfere with scaling and upgrades

• Add an Azure Spot node pool to an Azure Kubernetes Service (AKS) clusterlearn.microsoft.com
• Best Practices for Cost Optimization in Azure Kubernetes Service (AKS)learn.microsoft.com
• FinOps best practices for computelearn.microsoft.com
• Cost recommendations - Azure Advisorlearn.microsoft.com
• Cluster autoscaling in Azure Kubernetes Service (AKS) overviewlearn.microsoft.com
• Linux Virtual Machine Scale Sets pricingazure.microsoft.com