EC2 Fleet provides an API that allows to operate and procure capacity with quite granular controls. An EC2 Fleet contains the configuration information to launch a fleet or group of instances. Using EC2 Fleet, you can define separate On-Demand and Spot capacity targets, specify the instance types that work best for your applications, and specify how Amazon EC2 should distribute your fleet capacity within each purchasing model.
Workloads that can benefit from EC2 Fleet API are among other bespoke capacity orchestrators that implement tuned up and optimized logic to provision capacity. Just to name a few, the following projects use EC2 Fleet to manage capacity:
In this part of the workshop you tackle a common workload for with EC2 Fleet provides benefit when running.
Note that while using Spot Instances, most of MPI workloads, specially those that run for hours and do not use checkpointing, are not appropriate for Spot Instances. Remember Spot Instances are suited for fault tolerant applications that can recover from the loss and replacement of one or more instances.
In this part of the workshop you request an EC2 Fleet using the request type instant, which is a feature only available in EC2 Fleet. By doing so, EC2 Fleet places a synchronous one-time request for your desired capacity. In the API response, it returns the instances that launched, along with errors for those instances that could not be launched. More information on request types here.
Tightly coupled HPC workloads typically suffer from performance degradation when the instances in the cluster are of different instance families and sizes (i.e: c5.large vs c4.large or c5.large vs c5.xlarge). The other characteristic of this workload is that all the instances must be close together (ideally in the same placement group). To satisfy these constraints you configure the fleet request with same instance type (for example c5.large) in a single Availability Zone. If your HPC application is loosely coupled and you can remove these constraints and use Auto Scaling groups instead.
cat <<EoF > ./ec2-fleet-config.json
{
"SpotOptions":{
"SingleInstanceType": true,
"SingleAvailabilityZone": true,
"MinTargetCapacity": 4,
"AllocationStrategy": "price-capacity-optimized",
"InstanceInterruptionBehavior": "terminate"
},
"OnDemandOptions":{
"AllocationStrategy": "lowest-price",
"SingleInstanceType": true,
"SingleAvailabilityZone": true,
"MinTargetCapacity": 0
},
"LaunchTemplateConfigs":[
{
"LaunchTemplateSpecification":{
"LaunchTemplateId":"${LAUNCH_TEMPLATE_ID}",
"Version":"1"
},
"Overrides":[{
"InstanceRequirements": {
"VCpuCount": {
"Min": 2,
"Max": 4
},
"MemoryMiB": {
"Min": 0
},
"CpuManufacturers": [
"intel"
]
}
}]
}
],
"TargetCapacitySpecification":{
"TotalTargetCapacity": 4,
"OnDemandTargetCapacity": 0,
"DefaultTargetCapacityType": "spot"
},
"Type":"instant"
}
EoF
The EC2 Fleet request specifies separately the target capacity for Spot and On-Demand Instances using the OnDemandTargetCapacity and SpotTargetCapacity fields inside the TargetCapacitySpecification structure. The value for DefaultTargetCapacityType specifies whether Spot or On-Demand Instances should be used to meet the TotalTargetCapacity.
By setting SingleInstanceType and SingleAvailabilityZone to true, you are forcing the EC2 Fleet request to provision all the instances in the same Availability Zone and of the same type.
export FLEET_ID=$(aws ec2 create-fleet --cli-input-json file://ec2-fleet-config.json | jq -r '.FleetId')
You have now created an EC2 Fleet with request type instance!
Given the configuration you used above, try to answer the following questions. Click to expand and see the answers.
You have specified a value for MinTargetCapacity inside SpotOptions and OnDemandOptions structures. This parameter sets the minimum target capacity that needs to be reached. If it is not reached, the fleet launches no instances and the response provides an error indicating that the minimum request for instances could not be met.
Note that that by providing additional diversification, EC2 Fleet will check into more pools and be able to reach more capacity. Consider adding more diversification in those cases.
You can view the configuration parameters of your EC2 Fleet using this command:
aws ec2 describe-fleets --fleet-ids "${FLEET_ID}"
To describe one or more instances you use describe-fleets. To retrieve all the Spot Instances that have been launched by the EC2 Fleet, you apply two filters: instance-lifecycle set to spot to retrieve only Spot Instances and the custom tag aws:ec2:fleet-id that must be set to $FLEET_ID.
aws ec2 describe-instances --filters Name=instance-lifecycle,Values=spot Name=tag:aws:ec2:fleet-id,Values=${FLEET_ID} Name=instance-state-name,Values=running --query "Reservations[*].Instances[*].[InstanceId]" --output text
To check the newly created instances in the AWS Console, head to EC2 Dashboard home, click on “Instances (running), and filter the list of instances using aws:ec2:fleet-id = $FLEET_ID and Instance lifecycle = spot.
These are some of the features and characteristics that EC2 Fleet provides, in addition to the ones covered in this section:
instant mode, the mode you used during this workshop. A synchronous call that can be used as a drop-in-replacement for RunInstances but that offers a selection of pools and diversification using allocation strategies.maintain mode you can instruct EC2 Fleet to detect and replace un-healthy instances.