Developer Guide

Amazon EC2 Spot Instances Examples

This topic describes how to use the AWS SDK for .NET with Amazon EC2 Spot Instances.


Spot Instances enable you to bid on unused Amazon EC2 capacity and run any instances that you acquire for as long as your bid exceeds the current Spot Price. Amazon EC2 changes the Spot Price periodically based on supply and demand; customers whose bids meet or exceed it gain access to the available Spot Instances. Like On-Demand Instances and Reserved Instances, Spot Instances provide another option for obtaining more compute capacity.

Spot Instances can significantly lower your Amazon EC2 costs for applications such as batch processing, scientific research, image processing, video encoding, data and web crawling, financial analysis, and testing. Additionally, Spot Instances are an excellent option when you need large amounts of computing capacity, but the need for that capacity is not urgent.

To use Spot Instances, place a Spot Instance request specifying the maximum price you are willing to pay per instance hour; this is your bid. If your bid exceeds the current Spot Price, your request is fulfilled and your instances will run until either you choose to terminate them or the Spot Price increases above your bid (whichever is sooner). You can terminate a Spot Instance programmatically, as shown this tutorial, or by using the AWS Management Console or by using the AWS Toolkit for Visual Studio.

It's important to note two points:

  1. You will often pay less per hour than your bid. Amazon EC2 adjusts the Spot Price periodically as requests come in and available supply changes. Everyone pays the same Spot Price for that period regardless of whether their bid was higher. Therefore, you might pay less than your bid, but you will never pay more than your bid.

  2. If you're running Spot Instances and your bid no longer meets or exceeds the current Spot Price, your instances will be terminated. This means you will want to make sure that your workloads and applications are flexible enough to take advantage of this opportunistic—but potentially transient—capacity.

Spot Instances perform exactly like other Amazon EC2 instances while running, and like other Amazon EC2 instances, Spot Instances can be terminated when you no longer need them. If you terminate your instance, you pay for any partial hour used (as you would for On-Demand or Reserved Instances). However, if your instance is terminated by Amazon EC2 because the Spot Price goes above your bid, you will not be charged for any partial hour of use.

This tutorial provides an overview of how to use the .NET programming environment to do the following.

  • Submit a Spot request

  • Determine when the Spot request becomes fulfilled

  • Cancel the Spot request

  • Terminate associated instances


This tutorial assumes you have signed up for AWS, set up your .NET development environment, and installed the AWS SDK for .NET. If you use the Microsoft Visual Studio development environment, we recommend you also install the AWS Toolkit for Visual Studio. For instructions on setting up your environment, see Getting Started with the AWS SDK for .NET.

Setting Up Your Credentials

For information about how to use your AWS credentials with the SDK, see Configuring AWS Credentials.

Submitting Your Spot Request

To submit a Spot request, you first need to determine the instance type, the Amazon Machine Image (AMI), and the maximum bid price you want to use. You must also include a security group, so that you can log into the instance if you want to. For more information about creating security groups, see Creating a Security Group in Amazon EC2.

There are several instance types to choose from; go to Amazon EC2 Instance Types for a complete list. For this tutorial, we will use t1.micro. You'll also want to get the ID of a current Windows AMI. For more information, see Finding an AMI in the Amazon EC2 User Guide for Windows Instances.

There are many ways to approach bidding for Spot instances. To get a broad overview of the various approaches, you should view the Bidding for Spot Instances video. However, to get started, we'll describe three common strategies: bid to ensure cost is less than on-demand pricing; bid based on the value of the resulting computation; bid so as to acquire computing capacity as quickly as possible.

Reduce Cost Below On-Demand

You have a batch processing job that will take a number of hours or days to run. However, you are flexible with respect to when it starts and ends. You want to see if you can complete it for less than the cost of On-Demand Instances. You examine the Spot Price history for instance types using either the AWS Management Console or the Amazon EC2 API. For more information, go to Viewing Spot Price History. After you've analyzed the price history for your desired instance type in a given Availability Zone, you have two alternative approaches for your bid:

  • You could bid at the upper end of the range of Spot Prices (which are still below the On-Demand price), anticipating that your one-time Spot request would most likely be fulfilled and run for enough consecutive compute time to complete the job.

  • Or, you could bid at the lower end of the price range, and plan to combine many instances launched over time through a persistent request. The instances would run long enough, in aggregate, to complete the job at an even lower total cost. (We will explain how to automate this task later in this tutorial.)

Pay No More than the Value of the Result

You have a data processing job to run. You understand the value of the job's results well enough to know how much they are worth in terms of computing costs. After you've analyzed the Spot Price history for your instance type, you choose a bid price at which the cost of the computing time is no more than the value of the job's results. You create a persistent bid and allow it to run intermittently as the Spot Price fluctuates at or below your bid.

Acquire Computing Capacity Quickly

You have an unanticipated, short-term need for additional capacity that is not available through On-Demand Instances. After you've analyzed the Spot Price history for your instance type, you bid above the highest historical price to greatly improve the likelihood your request will be fulfilled quickly and continue computing until it is complete.

After you choose your bid price, you are ready to request a Spot Instance. For the purposes of this tutorial, we will set our bid price equal to the On-Demand price ($0.03) to maximize the chances the bid will be fulfilled. You can determine the types of available instances and the On-Demand prices for instances by going to Amazon EC2 Pricing page.

To request a Spot Instance, you need to build your request with the parameters we have specified so far. Start by creating a RequestSpotInstanceRequest object. The request object requires the bid price and the number of instances you want to start. Additionally, you need to set the LaunchSpecification for the request, which includes the instance type, AMI ID, and the name of the security group you want to use for the Spot Instances. After the request is populated, call the RequestSpotInstances method to create the Spot Instance request. The following example demonstrates how to request a Spot Instance.

public static SpotInstanceRequest RequestSpotInstance( AmazonEC2Client ec2Client, string amiId, string securityGroupName, InstanceType instanceType, string spotPrice, int instanceCount) { var request = new RequestSpotInstancesRequest(); request.SpotPrice = spotPrice; request.InstanceCount = instanceCount; var launchSpecification = new LaunchSpecification(); launchSpecification.ImageId = amiId; launchSpecification.InstanceType = instanceType; launchSpecification.SecurityGroups.Add(securityGroupName); request.LaunchSpecification = launchSpecification; var result = ec2Client.RequestSpotInstances(request); return result.SpotInstanceRequests[0]; }

The Spot request ID is contained in the SpotInstanceRequestId member of the SpotInstanceRequest object.

Running this code will launch a new Spot Instance request.


You will be charged for any Spot Instances that are launched, so make sure you cancel any requests and terminate any instances you launch to reduce any associated fees.

There are other options you can use to configure your Spot requests. To learn more, see RequestSpotInstances in the AWS SDK for .NET.

Determining the State of Your Spot Request

Next, we need to wait until the Spot request reaches the Active state before proceeding to the last step. To determine the state of your Spot request, we use the DescribeSpotInstanceRequests method to obtain the state of the Spot request ID we want to monitor.

public static SpotInstanceState GetSpotRequestState( AmazonEC2Client ec2Client, string spotRequestId) { // Create the describeRequest object with all of the request ids // to monitor (e.g. that we started). var request = new DescribeSpotInstanceRequestsRequest(); request.SpotInstanceRequestIds.Add(spotRequestId); // Retrieve the request we want to monitor. var describeResponse = ec2Client.DescribeSpotInstanceRequests(request); SpotInstanceRequest req = describeResponse.SpotInstanceRequests[0]; return req.State; }

Cleaning Up Your Spot Requests and Instances

The final step is to clean up your requests and instances. It is important to both cancel any outstanding requests and terminate any instances. Just canceling your requests will not terminate your instances, which means that you will continue to be charged for them. If you terminate your instances, your Spot requests may be canceled, but there are some scenarios, such as if you use persistent bids, where terminating your instances is not sufficient to stop your request from being re-fulfilled. Therefore, it is a best practice to both cancel any active bids and terminate any running instances.

You use the CancelSpotInstanceRequests method to cancel a Spot request. The following example demonstrates how to cancel a Spot request.

public static void CancelSpotRequest( AmazonEC2Client ec2Client, string spotRequestId) { var cancelRequest = new CancelSpotInstanceRequestsRequest(); cancelRequest.SpotInstanceRequestIds.Add(spotRequestId); ec2Client.CancelSpotInstanceRequests(cancelRequest); }

You use the TerminateInstances method to terminate an instance. The following example demonstrates how to obtain the instance identifier for an active Spot Instance and terminate the instance.

public static void TerminateSpotInstance( AmazonEC2Client ec2Client, string spotRequestId) { var describeRequest = new DescribeSpotInstanceRequestsRequest(); describeRequest.SpotInstanceRequestIds.Add(spotRequestId); // Retrieve the request we want to monitor. var describeResponse = ec2Client.DescribeSpotInstanceRequests(describeRequest); if (SpotInstanceState.Active == describeResponse.SpotInstanceRequests[0].State) { string instanceId = describeResponse.SpotInstanceRequests[0].InstanceId; var terminateRequest = new TerminateInstancesRequest(); terminateRequest.InstanceIds = new List<string>() { instanceId }; try { var terminateResponse = ec2Client.TerminateInstances(terminateRequest); } catch (AmazonEC2Exception ex) { // Check the ErrorCode to see if the instance does not exist. if ("InvalidInstanceID.NotFound" == ex.ErrorCode) { Console.WriteLine("Instance {0} does not exist.", instanceId); } else { // The exception was thrown for another reason, so re-throw the exception. throw; } } } }

For more information about terminating active instances, see Terminating an Amazon EC2 Instance.