Best practices for Amazon EC2 Spot

Amazon EC2 provides access to spare EC2 compute capacity in the AWS Cloud through Spot Instances at savings of up to 90% compared to On-Demand prices. The only difference between On-Demand Instances and Spot Instances is that Spot Instances can be interrupted by Amazon EC2, with two minutes of notice, if Amazon EC2 needs to reclaim the capacity. To ensure the best experience with Spot Instances, it's important to understand and apply best practices for their use.

Spot Instances are recommended for stateless, fault-tolerant, flexible applications. For example, Spot Instances work well for big data, containerized workloads, CI/CD, stateless web servers, high performance computing (HPC), and rendering workloads.

While running, Spot Instances are exactly the same as On-Demand Instances. However, Spot does not guarantee that you can keep your running instances long enough to finish your workloads. Spot also does not guarantee that you can get immediate availability of the instances that you are looking for, or that you can always get the aggregate capacity that you requested. Moreover, Spot Instance interruptions and capacity can change over time because Spot Instance availability varies based on supply and demand, and past performance isn’t a guarantee of future results.

Spot Instances are not suitable for workloads that are inflexible, stateful, fault-intolerant, or tightly coupled between instance nodes. We do not recommend Spot Instances for workloads that are intolerant of occasional periods when the entire target capacity is not completely available. While following Spot best practices to be flexible about instance types and Availability Zones provides the best chance for high availability, there are no guarantees that capacity will be available, because surges in demand for On-Demand Instances can disrupt workloads on Spot Instances.

We strongly discourage using Spot Instances for these workloads or attempting to fail over to On-Demand Instances to handle interruptions or periods of unavailability. Failing over to On-Demand Instances can inadvertently drive interruptions for your other Spot Instances. In addition if Spot Instances for a combination of instance type and Availability Zone get interrupted, it might become difficult for you to get On-Demand Instances with that same combination.

Regardless of whether you're an experienced Spot user or new to Spot Instances, if you are currently experiencing issues with Spot Instance interruptions or availability, we recommend that you follow these best practices to have the best experience using the Spot service.

Prepare individual instances for interruptions

The best way for you to gracefully handle Spot Instance interruptions is to architect your application to be fault-tolerant. To accomplish this, you can take advantage of EC2 instance rebalance recommendations and Spot Instance interruption notices.

An EC2 Instance rebalance recommendation is a signal that notifies you when a Spot Instance is at an elevated risk of interruption. The signal gives you the opportunity to proactively manage the Spot Instance in advance of the two-minute Spot Instance interruption notice. You can decide to rebalance your workload to new or existing Spot Instances that are not at an elevated risk of interruption. We've made it easy for you to use this signal by using the Capacity Rebalancing feature in Auto Scaling groups and EC2 Fleet.

A Spot Instance interruption notice is a warning that is issued two minutes before Amazon EC2 interrupts a Spot Instance. If your workload is "time-flexible," you can configure your Spot Instances to be stopped or hibernated, instead of being terminated, when they are interrupted. Amazon EC2 automatically stops or hibernates your Spot Instances on interruption, and automatically resumes the instances when we have available capacity.

We recommend that you create a rule in Amazon EventBridge that captures the rebalance recommendations and interruption notifications, and then triggers a checkpoint for the progress of your workload or gracefully handles the interruption. For more information, see Monitor rebalance recommendation signals. For a detailed example that walks you through how to create and use event rules, see Taking Advantage of Amazon EC2 Spot Instance Interruption Notices.

For more information, see EC2 instance rebalance recommendations and Spot Instance interruptions.

Be flexible about instance types and Availability Zones

A Spot capacity pool is a set of unused EC2 instances with the same instance type (for example, m5.large) and Availability Zone (for example, us-east-1a). You should be flexible about which instance types you request and in which Availability Zones you can deploy your workload. This gives Spot a better chance to find and allocate your required amount of compute capacity. For example, don't just ask for c5.large if you'd be willing to use larges from the c4, m5, and m4 families.

Depending on your specific needs, you can evaluate which instance types you can be flexible across to fulfill your compute requirements. If a workload can be vertically scaled, you should include larger instance types (more vCPUs and memory) in your requests. If you can only scale horizontally, you should include older generation instance types because they are less in demand from On-Demand customers.

A good rule of thumb is to be flexible across at least 10 instance types for each workload. In addition, make sure that all Availability Zones are configured for use in your VPC and selected for your workload.

Use attribute-based instance type selection

With attribute-based instance type selection, you can specify instance attributes—such as vCPUs, memory, and storage—for the workload you want to run. EC2 Auto Scaling or EC2 Fleet will then automatically identify and launch instances that match your specified attributes. This removes the effort required to manually select specific instance types, which requires an in-depth understanding of each instance type's offering.

Moreover, attribute-based instance type selection enables you to automatically use newly released instance types as they become available. This ensures seamless access to an increasingly broad range of Spot Instance capacity.

Attribute-based instance type selection is ideal for workloads and frameworks that can be flexible about the instance types they run on, such as High Performance Computing (HPC) and big data workloads.

For more information, see Create mixed instances group using attribute-based instance type selection in the Amazon EC2 Auto Scaling User Guide and Specify attributes for instance type selection for EC2 Fleet or Spot Fleet in this guide.

Use Spot placement scores to identify optimal Regions and Availability Zones

Spot Instances are unused EC2 capacity, and this capacity fluctuates based on EC2 supply and demand. As a result, you might not always get the exact Spot capacity that you require in a specific location at a specific time. To mitigate this unpredictability, you can use the Spot placement score feature. This feature provides recommendations for Regions or Availability Zones that are more likely to have sufficient capacity to meet your Spot capacity needs without requiring you to launch Spot Instances in those locations first.

Spot placement score is best used for workloads that can be flexible about the instance types and the Region or Availability Zone they can use. All you need to do is specify the Spot capacity that you need, your instance type requirements, and whether you want a recommendations for Regions or Availability Zones. In return, you receive a score ranging from 1 to 10 for each Region or Availability Zone, indicating the likelihood of successfully provisioning your requested Spot capacity in that location. A score of 10 indicates that your Spot request is highly likely to succeed.

It's important to note that a Spot placement score is a point-in-time recommendation, because capacity can vary over time. It does not guarantee available capacity or predict the risk of interruption.

You can use the Spot placement score feature in the Amazon EC2 console, AWS CLI, or an SDK. For more information, see Spot placement score.

Use EC2 Auto Scaling groups or EC2 Fleet to manage your aggregate capacity

Spot enables you to think in terms of aggregate capacity—in units that include vCPUs, memory, storage, or network throughput—rather than thinking in terms of individual instances. Auto Scaling groups and EC2 Fleet enable you to launch and maintain a target capacity, and to automatically request resources to replace any that are disrupted or manually terminated. When you configure an Auto Scaling group or an EC2 Fleet, you need only specify the instance types and target capacity based on your application needs. For more information, see Auto Scaling groups in the Amazon EC2 Auto Scaling User Guide and Create an EC2 Fleet in this user guide.

Use the price and capacity optimized allocation strategy

Allocation strategies in Auto Scaling groups help you to provision your target capacity without the need to manually look for the Spot capacity pools with spare capacity. We recommend using the price-capacity-optimized strategy because this strategy automatically provisions instances from the most-available Spot capacity pools that also have the lowest possible price. You can also take advantage of the price-capacity-optimized allocation strategy in EC2 Fleet. Because your Spot Instance capacity is sourced from pools with optimal capacity, this decreases the possibility that your Spot Instances are reclaimed. For more information about allocation strategies, see Spot Instances in the Amazon EC2 Auto Scaling User Guide and When workloads have a high cost of interruption in this user guide.

Use integrated AWS services to manage your Spot Instances

Other AWS services integrate with Spot to reduce overall compute costs without the need to manage the individual instances or fleets. We recommend that you consider the following solutions for your applicable workloads: Amazon EMR, Amazon Elastic Container Service, AWS Batch, Amazon Elastic Kubernetes Service, Amazon SageMaker, AWS Elastic Beanstalk, and Amazon GameLift. To learn more about Spot best practices with these services, see the Amazon EC2 Spot Instances Workshops Website.

Which is the best Spot request method to use?

Use the following table to determine which API to use when requesting Spot Instances.