We strongly discourage using the RequestSpotFleet API because it is a legacy API with no planned investment. If you want to manage your instance lifecycle, launch EC2 Spot instance via Auto Scaling group API. If you don’t want to manage your instance lifecycle, launch EC2 Spot instance via EC2 Fleet API. See Spot best practices for more details.
Spot Fleet allows you to diversify across different AZs and networks. However, unlike Auto Scaling groups, it does re-balance instances across AZs. Therefore, consider using Auto Scaling groups instead if AZ-rebalance is key for your workload. Spot Fleet supports types maintain and request. Similar to Auto Scaling groups, the maintain type preserves the number of instances by provisioning new healthy instances when it detects that one of the existing instances has become un-healthy.
To support mix instances with different types and purchasing options, Spot Fleet must use launch templates. In this exercise, you re-use the same launch template that you created before.
In this step, you go through a scenario that uses weights and target capacity. This maps well with the concept of “Compute Slots” in batch workloads. Some batch workloads can have more than one worker process running within an instance. The larger the instance, the more worker processes they can run. For example, one worker may consume 1 vCPU: 2GB Ram, which means that on a c5.xlarge (4 vCPUs: 8GB Ram), you could run up to 4 workers. The weight that you use for the c5.xlarge is 4.
By default, the Target Capacity attribute for Spot Fleet defines the number of instances that the Spot Fleet procures. When you use Spot Fleet weights, and associate a custom weight with an instance in the override section, the total target capacity is equivalent to the total target of weights that you give to the spot. Going back to the “Compute Slots” or vCPUs analogy, you can instruct Spot Fleet to provide a number of vCPUs or “Compute Slots” from many instances with different sizes.
While in the past weights were only supported on Spot Fleet and EC2 Fleet, now Auto Scaling groups also support weights and priorities. Therefore, we recommend using Auto Scaling groups for this type of workload as well.
To start with the hands on part, you first need to create a json file that sets a few relevant Spot parameters; One of the parameters is IamFleetRole. IamFleetRole must be set up to point to the ARN of an IAM role that grants the Spot Fleet the permission to request, launch, terminate, and tag instances on your behalf. For this purpose, you are going to first retrieve the ARN of the Service-Linked role named AWSServiceRoleForEC2SpotFleet. For more information read the spot fleet prerequisites.
If you have never launched a Spot Fleet, the AWSServiceRoleForEC2SpotFleet won’t exist in your account. To create it run the following command in AWS CloudShell: aws iam create-service-linked-role --aws-service-name spotfleet.amazonaws.com
Execute the following command to export the ARN of the Service-Linked role to an environment variable.
export EC2_SPOT_ROLE=$(aws iam get-role --role-name AWSServiceRoleForEC2SpotFleet | jq -r '.Role.Arn')
Copy and paste the following in AWS CloudShell to generate the configuration file:
cat <<EoF > ./spot-fleet-request-config.json
{
"AllocationStrategy": "priceCapacityOptimized",
"OnDemandAllocationStrategy": "prioritized",
"SpotMaintenanceStrategies": {
"CapacityRebalance": {
"ReplacementStrategy": "launch"
}
},
"LaunchTemplateConfigs": [
{
"LaunchTemplateSpecification": {
"LaunchTemplateId": "${LAUNCH_TEMPLATE_ID}",
"Version": "1"
},
"Overrides":[
{
"InstanceType":"c5.large",
"WeightedCapacity": 2.0,
"Priority": 3.0
},
{
"InstanceType":"m5.large",
"WeightedCapacity": 2.0,
"Priority": 2.0
},
{
"InstanceType":"r5.large",
"WeightedCapacity": 2.0,
"Priority": 1.0
},
{
"InstanceType":"c5.xlarge",
"WeightedCapacity": 4.0,
"Priority": 6.0
},
{
"InstanceType":"m5.xlarge",
"WeightedCapacity": 4.0,
"Priority": 5.0
},
{
"InstanceType":"r5.xlarge",
"WeightedCapacity": 4.0,
"Priority": 4.0
}
]
}
],
"IamFleetRole": "${EC2_SPOT_ROLE}",
"TargetCapacity": 12,
"OnDemandTargetCapacity": 4,
"TerminateInstancesWithExpiration": true,
"Type": "maintain",
"ReplaceUnhealthyInstances": true
}
EoF
Note how the Spot Fleet request file specifies the TargetCapacity and OnDemandTargetCapacity. The split between those two will go into Spot capacity (i.e: to have all on Spot capacity, just set the OnDemandTargetCapacity to 0).
When AllocationStrategy is set to priceCapacityOptimized, Spot Fleet launches instances from optimal Spot pools for the target capacity of instances (in this case weights) that you are launching. Spot Fleet then requests Spot Instances from the lowest priced of these pools.
Spot Fleet does support CapacityRebalance as part of the Metadata service. CapacityRebalance is a signal that EC2 emits when a Spot instance is at an elevated risk of being interrupted. Users can intercept this event and decide if they want to launch a replacement by selecting launch as the ReplacementStrategy within the SpotMaintenanceStrategies structure.
By specifying maintain as the request type, Spot Fleet places requests to meet the target capacity over time and automatically replenish any interrupted instances.
If you want to learn more about the other configuration parameters, you can review the documentation here.
Once that you’ve read and familiarised yourself with the configuration, copy and paste this command to submit the Spot Fleet request and export its identifier to an environment variable.
export SPOT_FLEET_REQUEST_ID=$(aws ec2 request-spot-fleet --spot-fleet-request-config file://spot-fleet-request-config.json | jq -r '.SpotFleetRequestId')
You have now created a Spot Fleet that uses weights and combines Spot and On-Demand Instances to meet the specified target capacity.
Given the configuration you used above. Try to answer the following questions.
This Spot Fleet will maintain a weighted target capacity of 12, as specified in the value for TargetCapacity. Additionally, you are specifying an On-Demand target capacity of 4. Remember that Amazon EC2 calculates the difference between the total capacity and On-Demand capacity in order to launch Spot Instances. This would result in 1 On-Demand Instance being launched and in the case of Spot Instances, given that you are using priceCapacityOptimized allocation strategy, a few things may happen; the most common is that out of the 18 pools, one is selected as optimal (has more capacity, etc). If the selected pool is one of the 9 pools defined as large, 4 Spot Instances will be added. If the pool selected is one of the 9 xlarge, 2 Spot Instances will be created.
You specified prioritized as the allocation strategy for On-Demand Instances. Therefore, the order in which Spot Fleet will attempt to fulfill the On-Demand capacity is defined by the value of Priority in the list of overrides. It will aim first to launch capacity from the c5.xlarge pools with the highest priority. If there are Insufficient Capacity Errors, it will go into the pools with the next higher priority m5.xlarge, and so on.
For Spot, the priority attribute will have no effect in the example. You have specified priceCapacityOptimized as allocation strategy to follow the best practices associated with Spot. This will make the Spot Fleet launch instances from Spot Instance pools with optimal capacity.
While the command below will provide us the description of the Spot Fleet Request
aws ec2 describe-spot-fleet-requests --spot-fleet-request-ids=$SPOT_FLEET_REQUEST_ID
To get the description of the instances and what happened over time to the request you can use:
aws ec2 describe-spot-fleet-instances --spot-fleet-request-id=$SPOT_FLEET_REQUEST_ID
There is also a describe-spot-fleet-request-history that will showcase the steps the fleet took to procure the capacity. You can request it using the following command.
aws ec2 describe-spot-fleet-request-history --spot-fleet-request-id=$SPOT_FLEET_REQUEST_ID --start-time=$(date '+%m-%d-%YT%H:%M:%S' -d '-1 hour')
These are some of the features and characteristics that Spot Fleet provides, in addition to the ones covered in this section:
LaunchTemplateConfigs section of the configuration file. By doing so, you can launch a Spot Fleet with instances that vary by instance type, AMI, Availability Zone or subnet.You can read more about Spot Fleet here, in the AWS Spot Fleet documentation.