Spot Instances enable you to take advantage of excess capacity in AWS/Azure, offering significant discounts compared to standard pricing. Instead of fixed pricing, Spot Instances allow you to bid on unused VM capacity.
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Spot Instances Overview
The pricing of Spot Instances is variable and determined by supply and demand.
When demand for computing resources is low, you can bid for these unused resources at a fraction of the standard price.
The trade-off for this discount is that AWS/Azure may reclaim Spot Instances with two minutes' notice if the capacity is needed for On-Demand instances.
Spot Instances are best suited for workloads that can handle interruptions and are not time-sensitive, stateless, and fault-tolerant.
If the Spot Instance price exceeds your maximum bid price, your workload will be interrupted.
Use Cases
Common use cases for Spot Instances include:
Workloads that can be interrupted and don’t need to be completed within a specific time frame.
Work that can be easily restarted or reprocessed.
High-performance computing and batch processing.
Dev and test/sandbox environments.
Large stateless applications.
You can save up-to 90% on On-Demand prices.
It’s a purchasing option that allows users to take advantage of EC2 spare capacity at a low price (determined by long term trends in supply and demand).
BUT it could be reclaimed for other workloads with just a two-minute notice.
Also, if the price goes above your maximum set price, your workload will also be interrupted.
This means that workloads need to be specifically designed for fault tolerance, even if AWS claims that spot instances are interrupted less than 5% of the time.
How to identify?
In AWS Console, go to the EC2 service, then select the Spot Fleets section.
Spot Fleets are collections of instances, including Spot Instances and optionally On-Demand Instances.
When provisioning a Spot Fleet, you can set a target capacity for the fleet, and the request will be fulfilled if there is available capacity.
Mitigate cost risks by setting a maximum cost per hour for the entire fleet.
How to fix?
Ensure your workload is fault-tolerant.
Prepare your workload to restart or reprocess if interrupted.
In AWS Console, go to the EC2 service and create a Spot Fleet Request.
Define a target capacity and a maximum cost.
Optionally, specify that Amazon EC2 hibernates your Spot Instances when interrupted (memory is saved to the root EBS volume and reloaded when the instance resumes).
If the resource is provisioned automatically via IaC (such as CloudFormation or Terraform), update the corresponding code to reflect the changes.