An AWS Spot Fleet (Amazon Web Services Spot Fleets) is a collection of virtual servers purchased at reduced rates within Amazon Elastic Compute Cloud (EC2), which also manages those servers, which are called instances. Single instances are sold under the name AWS Spot Instance.
Spot Fleets eliminate the need for applications to manually respond to events or poll the instances the applications are running on. Requests for Spot Fleets are made using the Spot Fleet API or through the command-line interface (CLI). Users request a Spot Fleet by specifying the maximum desired price per instance hour, target capacity and launch specifications such as the number of instances desired, instance types and availability zones. Prices of Spot Instances constantly change, but EC2 attempts to maintain the requested target capacity of the Spot Fleet. EC2 terminates Spot Instances as prices rise above user-defined settings and launches replacement instances at the new lowest-priced option available for an another acceptable instance type.
Optional values for Spot Fleet requests include client tokens, creation date and end date. AWS selects the lowest-priced instances available to fulfill a Spot Fleet request. AWS automates management of these instance collections. Spot Fleet requests are active until canceled by a user, but canceling a fleet does not individually affect instances unless specified in configurations. Users must specify an Identity and Access Management (IAM) role to allow the Spot Fleet service to automatically terminate instances.
Amazon places limits on the number of fleet instances launched within EC2. AWS also places limits on spot bid prices, instances and volume.