Spot Instance interruptions

You can launch Spot Instances on spare EC2 capacity for steep discounts in exchange for returning them when Amazon EC2 needs the capacity back. When Amazon EC2 reclaims a Spot Instance, we call this event a Spot Instance interruption.

Demand for Spot Instances can vary significantly from moment to moment, and the availability of Spot Instances can also vary significantly depending on how many unused EC2 instances are available. It is always possible that your Spot Instance might be interrupted. Therefore, you must ensure that your application is prepared for a Spot Instance interruption.

An On-Demand Instance specified in an EC2 Fleet or Spot Fleet cannot be interrupted.

Reasons for interruption

The following are the possible reasons that Amazon EC2 might interrupt your Spot Instances:

• Price – The Spot price is greater than your maximum price.

• Capacity – Amazon EC2 can interrupt your Spot Instance when it needs it back. EC2 reclaims your instance mainly to repurpose capacity, but it can also occur for other reasons such as host maintenance or hardware decommission.

• Constraints – If your request includes a constraint such as a launch group or an Availability Zone group, these Spot Instances are terminated as a group when the constraint can no longer be met.

You can see the historical interruption rates for your instance type in the Spot Instance Advisor.

Interruption behaviors

You can specify that Amazon EC2 must do one of the following when it interrupts a Spot Instance:

• Stop interrupted Spot Instances

• Hibernate interrupted Spot Instances

• Terminate interrupted Spot Instances (this is the default behavior)

To change the interruption behavior, see Specify the interruption behavior.

Stop interrupted Spot Instances

Prerequisites

You can specify the interruption behavior so that Amazon EC2 stops Spot Instances when they are interrupted if the following prerequisites are met.

• Spot Instance request type – must be persistent. You can't specify a launch group in the Spot Instance request.

• EC2 Fleet or Spot Fleet request type – must be maintain

• Root volume type – must be an EBS volume, not an instance store volume

After a Spot Instance is stopped by the Spot service, only the Spot service can restart the Spot Instance, and the same launch specification must be used.

For a Spot Instance launched by a persistent Spot Instance request, the Spot service restarts the stopped instance when capacity is available in the same Availability Zone and for the same instance type as the stopped instance.

If instances in an EC2 Fleet or Spot Fleet are stopped and the fleet is of type maintain, the Spot service launches replacement instances to maintain the target capacity. The Spot service finds the best Spot capacity pools based on the specified allocation strategy (lowestPrice, diversified, or InstancePoolsToUseCount); it does not prioritize the pool with the earlier stopped instances. Later, if the allocation strategy leads to a pool containing the earlier stopped instances, the Spot service restarts the stopped instances to meet the target capacity.

For example, consider a Spot Fleet with the lowestPrice allocation strategy. At initial launch, a c3.large pool meets the lowestPrice criteria for the launch specification. Later, when the c3.large instances are interrupted, the Spot service stops the instances and replenishes capacity from another pool that fits the lowestPrice strategy. This time, the pool happens to be a c4.large pool and the Spot service launches c4.large instances to meet the target capacity. Similarly, Spot Fleet could move to a c5.large pool the next time. In each of these transitions, the Spot service does not prioritize pools with earlier stopped instances, but rather prioritizes purely on the specified allocation strategy. The lowestPrice strategy can lead back to pools with earlier stopped instances. For example, if instances are interrupted in the c5.large pool and the lowestPrice strategy leads it back to the c3.large or c4.large pools, the earlier stopped instances are restarted to fulfill target capacity.

While a Spot Instance is stopped, you can modify some of its instance attributes, but not the instance type. If you detach or delete an EBS volume, it is not attached when the Spot Instance is started. If you detach the root volume and the Spot service attempts to start the Spot Instance, instance start fails and the Spot service terminates the stopped instance.

You can terminate a Spot Instance while it is stopped. If you cancel a Spot Instance request, an EC2 Fleet, or a Spot Fleet, the Spot service terminates any associated Spot Instances that are stopped.

While a Spot Instance is stopped, you are charged only for the EBS volumes, which are preserved. With EC2 Fleet and Spot Fleet, if you have many stopped instances, you can exceed the limit on the number of EBS volumes for your account.

Hibernate interrupted Spot Instances

Hibernation prerequisites

You can specify the interruption behavior so that Amazon EC2 hibernates Spot Instances when they are interrupted if the following prerequisites are met.

• Spot Instance request type – must be persistent. You can't specify a launch group in the Spot Instance request.

• EC2 Fleet or Spot Fleet request type – must be maintain

• Supported instance families – C3, C4, C5, M4, M5, R3, R4

• Instance RAM size – must be less than 100 GB

• Supported operating systems (You must install the hibernation agent on a supported operating system. Alternatively, use a supported AMI, which already includes the agent.):

  • Amazon Linux 2

  • Amazon Linux AMI

  • Ubuntu with an AWS-tuned Ubuntu kernel (linux-aws) greater than 4.4.0-1041

  • Windows Server 2008 R2 and later

• Supported AMIs (the following supported AMIs include the hibernation agent):

  • Amazon Linux 2

  • Amazon Linux AMI 2017.09.1 or later

  • Ubuntu Xenial 16.04 20171121 or later

  • Windows Server 2008 R2 AMI 2017.11.19 or later

  • Windows Server 2012 or Windows Server 2012 R2 AMI 2017.11.19 or later

  • Windows Server 2016 AMI 2017.11.19 or later

  • Windows Server 2019

• Root volume type – must be an EBS volume, not an instance store volume, and it must be large enough to store the instance memory (RAM) during hibernation

• Start the hibernation agent – We recommend that you use user data to start the agent on instance startup. Alternatively, you could start the agent manually.

Recommendation

• We strongly recommend that you use an encrypted Amazon EBS volume as the root volume, because instance memory is stored on the root volume during hibernation. This ensures that the contents of memory (RAM) are encrypted when the data is at rest on the volume and when data is moving between the instance and volume. Use one of the following three options to ensure that the root volume is an encrypted Amazon EBS volume:

  • EBS “single-step” encryption: In a single run-instances API call, you can launch encrypted EBS-backed EC2 instances from an unencrypted AMI. For more information, see Use encryption with EBS-backed AMIs.

  • EBS encryption by default: You can enable EBS encryption by default to ensure all new EBS volumes created in your AWS account are encrypted. For more information, see Encryption by default.

  • Encrypted AMI: You can enable EBS encryption by using an encrypted AMI to launch your instance. If your AMI does not have an encrypted root snapshot, you can copy it to a new AMI and request encryption. For more information, see Encrypt an unencrypted image during copy and Copy an AMI.

When a Spot Instance is hibernated by the Spot service, the EBS volumes are preserved and instance memory (RAM) is preserved on the root volume. The private IP addresses of the instance are also preserved. Instance storage volumes and public IP addresses, other than Elastic IP addresses, are not preserved. While the instance is hibernating, you are charged only for the EBS volumes. With EC2 Fleet and Spot Fleet, if you have many hibernated instances, you can exceed the limit on the number of EBS volumes for your account.

The agent prompts the operating system to hibernate when the instance receives a signal from the Spot service. If the agent is not installed, the underlying operating system doesn't support hibernation, or there isn't enough volume space to save the instance memory, hibernation fails and the Spot service stops the instance instead.

When the Spot service hibernates a Spot Instance, you receive an interruption notice, but you do not have two minutes before the Spot Instance is interrupted. Hibernation begins immediately. While the instance is in the process of hibernating, instance health checks might fail. When the hibernation process completes, the state of the instance is stopped.

Resuming a hibernated Spot Instance

After a Spot Instance is hibernated by the Spot service, it can only be resumed by the Spot service. The Spot service resumes the instance when capacity becomes available with a Spot price that is less than your specified maximum price.

For more information, see Prepare for instance hibernation.

For information about hibernating On-Demand Instances, see Hibernate your On-Demand or Reserved Linux instance.

Specify the interruption behavior

If you do not specify an interruption behavior, the default is to terminate Spot Instances when they are interrupted. You can specify the interruption behavior when you create a Spot Instance request. The way in which you specify the interruption behavior is different depending on how you request Spot Instances.

If you request Spot Instances using the launch instance wizard, you can specify the interruption behavior as follows: Select the Persistent request check box and then, from Interruption behavior, choose an interruption behavior.

If you request Spot Instances using the Spot console, you can specify the interruption behavior as follows: Select the Maintain target capacity check box and then, from Interruption behavior, choose an interruption behavior.

If you configure Spot Instances in a launch template, you can specify the interruption behavior as follows: In the launch template, expand Advanced details and select the Request Spot Instances check box. Choose Customize and then, from Interruption behavior, choose an interruption behavior.

If you configure Spot Instances in a launch configuration when using the request-spot-fleet CLI, you can specify the interruption behavior as follows: For InstanceInterruptionBehavior, specify an interruption behavior.

If you configure Spot Instances using the request-spot-instances CLI, you can specify the interruption behavior as follows: For --instance-interruption-behavior, specify an interruption behavior.

Prepare for interruptions

Here are some best practices to follow when you use Spot Instances:

• Use the default maximum price, which is the On-Demand price.

• Ensure that your instance is ready to go as soon as the request is fulfilled by using an Amazon Machine Image (AMI) that contains the required software configuration. You can also use user data to run commands at start-up.

• Store important data regularly in a place that isn't affected when the Spot Instance terminates. For example, you can use Amazon S3, Amazon EBS, or DynamoDB.

• Divide the work into small tasks (using a Grid, Hadoop, or queue-based architecture) or use checkpoints so that you can save your work frequently.

• Amazon EC2 emits a rebalance recommendation signal to the Spot Instance when the instance is at an elevated risk of interruption. You can rely on the rebalance recommendation to proactively manage Spot Instance interruptions without having to wait for the two-minute Spot Instance interruption notice. For more information, see EC2 instance rebalance recommendations.

• Use the two-minute Spot Instance interruption notices to monitor the status of your Spot Instances. For more information, see Spot Instance interruption notices.

• While we make every effort to provide these warnings as soon as possible, it is possible that your Spot Instance is interrupted before the warnings can be made available. Test your application to ensure that it handles an unexpected instance interruption gracefully, even if you are monitoring for rebalance recommendation signals and interruption notices. You can do so by running the application using an On-Demand Instance and then terminating the On-Demand Instance yourself.

Prepare for instance hibernation

You must install a hibernation agent on your instance, unless you used an AMI that already includes the agent. You must run the agent on instance startup, whether the agent was included in your AMI or you installed it yourself.

The following procedures help you prepare a Linux instance. For directions to prepare a Windows instance, see Prepare for instance hibernation in the Amazon EC2 User Guide for Windows Instances.

To prepare an Amazon Linux instance

1. Verify that your kernel supports hibernation and update the kernel if necessary.

2. If your AMI doesn't include the agent, install the agent using the following command.

   sudo yum update; sudo yum install hibagent

3. Add the following to the user data:

   #!/bin/bash
   /usr/bin/enable-ec2-spot-hibernation

To prepare an Ubuntu instance

1. If your AMI doesn't include the agent, install the agent using the following command. The hibernation agent is only available on Ubuntu 16.04 or later.

   sudo apt-get install hibagent

2. Add the following to the user data.

   #!/bin/bash
   /usr/bin/enable-ec2-spot-hibernation

Spot Instance interruption notices

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 Spot Instance interruption notices. A Spot Instance interruption notice is a warning that is issued two minutes before Amazon EC2 stops or terminates your Spot Instance. If you specify hibernation as the interruption behavior, you receive an interruption notice, but you do not receive a two-minute warning because the hibernation process begins immediately.

We recommend that you check for these interruption notices every 5 seconds.

The interruption notices are made available as a CloudWatch event and as items in the instance metadata on the Spot Instance. Events are emitted on a best effort basis.

EC2 Spot Instance interruption notice

When Amazon EC2 is going to interrupt your Spot Instance, it emits an event two minutes prior to the actual interruption (except for hibernation, which gets the interruption notice, but not two minutes in advance, because hibernation begins immediately). This event can be detected by Amazon CloudWatch Events. For more information about CloudWatch events, see the Amazon CloudWatch Events User Guide. 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.

The following is an example of the event for Spot Instance interruption. The possible values for instance-action are hibernate, stop, and terminate.

{
    "version": "0",
    "id": "12345678-1234-1234-1234-123456789012",
    "detail-type": "EC2 Spot Instance Interruption Warning",
    "source": "aws.ec2",
    "account": "123456789012",
    "time": "yyyy-mm-ddThh:mm:ssZ",
    "region": "us-east-2",
    "resources": ["arn:aws:ec2:us-east-2:123456789012:instance/i-1234567890abcdef0"],
    "detail": {
        "instance-id": "i-1234567890abcdef0",
        "instance-action": "action"
    }
}

instance-action

If your Spot Instance is marked to be stopped or terminated by the Spot service, the instance-action item is present in your instance metadata. Otherwise, it is not present. You can retrieve instance-action as follows.

IMDSv2

[ec2-user ~]$ TOKEN=`curl -X PUT "http://169.254.169.254/latest/api/token" -H "X-aws-ec2-metadata-token-ttl-seconds: 21600"` \
&& curl -H "X-aws-ec2-metadata-token: $TOKEN" –v http://169.254.169.254/latest/meta-data/spot/instance-action

IMDSv1

[ec2-user ~]$ curl http://169.254.169.254/latest/meta-data/spot/instance-action

The instance-action item specifies the action and the approximate time, in UTC, when the action will occur.

The following example indicates the time at which this instance will be stopped.

{"action": "stop", "time": "2017-09-18T08:22:00Z"}

The following example indicates the time at which this instance will be terminated.

{"action": "terminate", "time": "2017-09-18T08:22:00Z"}

If Amazon EC2 is not preparing to stop or terminate the instance, or if you terminated the instance yourself, instance-action is not present and you receive an HTTP 404 error when you try to retrieve it.

termination-time

This item is maintained for backward compatibility; you should use instance-action instead.

If your Spot Instance is marked for termination by the Spot service, the termination-time item is present in your instance metadata. Otherwise, it is not present. You can retrieve termination-time as follows.

IMDSv2

[ec2-user ~]$ TOKEN=`curl -X PUT "http://169.254.169.254/latest/api/token" -H "X-aws-ec2-metadata-token-ttl-seconds: 21600"`
[ec2-user ~]$ if curl -H "X-aws-ec2-metadata-token: $TOKEN" -s http://169.254.169.254/latest/meta-data/spot/termination-time | grep -q .*T.*Z; then echo terminated; fi

IMDSv1

[ec2-user ~]$ if curl -s http://169.254.169.254/latest/meta-data/spot/termination-time | grep -q .*T.*Z; then echo terminated; fi

The termination-time item specifies the approximate time in UTC when the instance receives the shutdown signal. For example:

2015-01-05T18:02:00Z

If Amazon EC2 is not preparing to terminate the instance, or if you terminated the Spot Instance yourself, the termination-time item is either not present (so you receive an HTTP 404 error) or contains a value that is not a time value.

If Amazon EC2 fails to terminate the instance, the request status is set to fulfilled. The termination-time value remains in the instance metadata with the original approximate time, which is now in the past.

Find interrupted Spot Instances

In the console, the Instances pane displays all instances, including Spot Instances. You can identify a Spot Instance from the spot value in the Instance lifecycle column. The Instance state column indicates whether the instance is pending, running, stopping, stopped, shutting-down, or terminated. For a hibernated Spot Instance, the instance state is stopped.

To find an interrupted Spot Instance (console)

1. Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/.

2. In the navigation pane, choose Instances. In the top right corner, choose the settings icon ( ), and under Attribute columns, select Instance lifecycle. For Spot Instances, Instance lifecycle is spot.

   Alternatively, in the navigation pane, choose Spot Requests. You can see both Spot Instance requests and Spot Fleet requests. To view the IDs of the instances, select a Spot Instance request or a Spot Fleet request and choose the Instances tab. Choose an instance ID to display the instance in the Instances pane.

3. For each Spot Instance, you can view its state in the Instance State column.

To find interrupted Spot Instances (AWS CLI)

You can list your interrupted Spot Instances using the describe-instances command with the --filters parameter. To list only the instance IDs in the output, add the --query parameter.

aws ec2 describe-instances \
    --filters Name=instance-lifecycle,Values=spot Name=instance-state-name,Values=terminated,stopped \
    --query "Reservations[*].Instances[*].InstanceId"

Determine whether Amazon EC2 interrupted a Spot Instance

If a Spot Instance is stopped, hibernated, or terminated, you can use CloudTrail to see whether Amazon EC2 interrupted the Spot Instance. In AWS CloudTrail, the event name BidEvictedEvent indicates that Amazon EC2 interrupted the Spot Instance.

To view BidEvictedEvent events in CloudTrail

1. Open the CloudTrail console at https://console.aws.amazon.com/cloudtrail/.

2. In the navigation pane, choose Event history.

3. In the filter drop-down, choose Event name, and then in the filter field to the right, enter BidEvictedEvent.

4. Choose BidEvictedEvent in the resulting list to view its details. Under Event record, you can find the instance ID.

For more information about using CloudTrail, see Log Amazon EC2 and Amazon EBS API calls with AWS CloudTrail.

Billing for interrupted Spot Instances

When a Spot Instance is interrupted, you’re charged as follows.

Who interrupts the Spot Instance	Operating system	Interrupted in the first hour	Interrupted in any hour after the first hour
If you stop or terminate the Spot Instance	Windows and Linux (excluding RHEL and SUSE)	Charged for the seconds used	Charged for the seconds used
	RHEL and SUSE	Charged for the full hour even if you used a partial hour	Charged for the full hours used, and charged a full hour for the interrupted partial hour
If the Amazon EC2 Spot service interrupts the Spot Instance	Windows and Linux (excluding RHEL and SUSE)	No charge	Charged for the seconds used
	RHEL and SUSE	No charge	Charged for the full hours used, but no charge for the interrupted partial hour