# Amazon EC2 On-Demand or Amazon EC2 Spot Most AWS Batch customers use Amazon EC2 Spot instances because of the savings over On-Demand instances. However, if your workload runs for multiple hours and can't be interrupted, On-Demand instances might be more suitable for you. You can always try Spot instances first and switch to On-Demand if necessary. If you have the following requirements and expectations, use Amazon EC2 On-Demand instances: + The runtime of your jobs is more than an hour, and you can't tolerate interruptions to your workload. + You have a strict SLO (service-level objective) for your overall workload and can’t increase computational time. + The instances that you require are more likely to see interruptions. If you have the following requirements and expectations, use Amazon EC2 Spot instances: + The runtime for your jobs is typically 30 minutes or less. + You can tolerate potential interruptions and job rescheduling as a part of your workload. For more information, see [Spot Instance advisor](https://aws.amazon.com/ec2/spot/instance-advisor/). + Long running jobs can be restarted from a checkpoint if interrupted. You can mix both purchasing models by submitting on Spot instance first and then use On-Demand instance as a fallback option. For example, submit your jobs on a queue that's connected to compute environments that are running on Amazon EC2 Spot instances. If a job gets interrupted, catch the event from Amazon EventBridge and correlate it to a Spot instance reclamation. Then, resubmit the job to an On-Demand queue using an AWS Lambda function or AWS Step Functions. For more information, see [Tutorial: Sending Amazon Simple Notification Service alerts for failed job events](batch_sns_tutorial.md), [Best practices for handling Amazon EC2 Spot Instance interruptions](https://aws.amazon.com/blogs/compute/best-practices-for-handling-ec2-spot-instance-interruptions/) and [ Manage AWS Batch with Step Functions](https://docs.aws.amazon.com/step-functions/latest/dg/connect-batch.html). **Important** Use different instance types, sizes, and Availability Zones for your On-Demand compute environment to maintain Amazon EC2 Spot instance pool availability and decrease the interruption rate.