How Spot placement score works - Amazon Elastic Compute Cloud
Step 1: Specify your Spot requirementsStep 2: Filter the Spot placement score responseStep 3: Review the recommendationsStep 4: Use the recommendations

How Spot placement score works

When you use the Spot placement score feature, you first specify your compute requirements for your Spot Instances, and then Amazon EC2 returns the top 10 Regions or Availability Zones where your Spot request is likely to succeed. Each Region or Availability Zone is scored on a scale from 1 to 10, with 10 indicating that your Spot request is highly likely to succeed, and 1 indicating that your Spot request is not likely to succeed.

Step 1: Specify your Spot requirements

First, you specify your desired target Spot capacity and your compute requirements, as follows:

  1. Specify the target Spot capacity, and optionally the target capacity unit.

    You can specify your desired target Spot capacity in terms of the number of instances or vCPUs, or in terms of the amount of memory in MiB. To specify the target capacity in number of vCPUs or amount of memory, you must specify the target capacity unit as vcpu or memory-mib. Otherwise, it defaults to number of instances.

    By specifying your target capacity in terms of the number of vCPUs or the amount of memory, you can use these units when counting the total capacity. For example, if you want to use a mix of instances of different sizes, you can specify the target capacity as a total number of vCPUs. The Spot placement score feature then considers each instance type in the request by its number of vCPUs, and counts the total number of vCPUs rather than the total number of instances when totaling up the target capacity.

    For example, say you specify a total target capacity of 30 vCPUs, and your instance type list consists of c5.xlarge (4 vCPUs), m5.2xlarge (8 vCPUs), and r5.large (2 vCPUs). To achieve a total of 30 vCPUs, you could get a mix of 2 c5.xlarge (2*4 vCPUs), 2 m5.2xlarge (2*8 vCPUs), and 3 r5.large (3*2 vCPUs).

  2. Specify instance types or instance attributes.

    You can either specify the instance types to use, or you can specify the instance attributes that you need for your compute requirements, and then let Amazon EC2 identify the instance types that have those attributes. This is known as attribute-based instance type selection.

    You can't specify both instance types and instance attributes in the same Spot placement score request.

    If you specify instance types, you must specify at least three different instance types, otherwise Amazon EC2 will return a low Spot placement score. Similarly, if you specify instance attributes, they must resolve to at least three different instance types.

For examples of different ways to specify your Spot requirements, see Example configurations.

Step 2: Filter the Spot placement score response

Amazon EC2 calculates the Spot placement score for each Region or Availability Zone, and returns either the top 10 Regions or the top 10 Availability Zones where your Spot request is likely to succeed. The default is to return a list of scored Regions. If you plan to launch all of your Spot capacity into a single Availability Zone, then it's useful to request a list of scored Availability Zones.

You can specify a Region filter to narrow down the Regions that will be returned in the response.

You can combine the Region filter and a request for scored Availability Zones. In this way, the scored Availability Zones are confined to the Regions for which you've filtered. To find the highest-scored Availability Zone in a Region, specify only that Region, and the response will return a scored list of all of the Availability Zones in that Region.

Step 3: Review the recommendations

The Spot placement score for each Region or Availability Zone is calculated based on the target capacity, the composition of the instance types, the historical and current Spot usage trends, and the time of the request. Because Spot capacity is constantly fluctuating, the same Spot placement score request can yield different scores when calculated at different times.

Regions and Availability Zones are scored on a scale from 1 to 10. A score of 10 indicates that your Spot request is highly likely—but not guaranteed—to succeed. A score of 1 indicates that your Spot request is not likely to succeed at all. The same score might be returned for different Regions or Availability Zones.

If low scores are returned, you can edit your compute requirements and recalculate the score. You can also request Spot placement score recommendations for the same compute requirements at different times of the day.

Step 4: Use the recommendations

A Spot placement score is only relevant if your Spot request has exactly the same configuration as the Spot placement score configuration (target capacity, target capacity unit, and instance types or instance attributes), and is configured to use the capacity-optimized allocation strategy. Otherwise, the likelihood of getting available Spot capacity will not align with the score.

While a Spot placement score serves as a guideline, and no score guarantees that your Spot request will be fully or partially fulfilled, you can use the following information to get the best results:

  • Use the same configuration – The Spot placement score is relevant only if the Spot request configuration (target capacity, target capacity unit, and instance types or instance attributes) in your Auto Scaling group, EC2 Fleet, or Spot Fleet is the same as what you entered to get the Spot placement score.

    If you used attribute-based instance type selection in your Spot placement score request, you can use attribute-based instance type selection to configure your Auto Scaling group, EC2 Fleet, or Spot Fleet. For more information, see Create mixed instances group using attribute-based instance type selection and Specify attributes for instance type selection for EC2 Fleet or Spot Fleet.

    Note

    If you specified your target capacity in terms of the number of vCPUs or the amount of memory, and you specified instance types in your Spot placement score configuration, note that you can’t currently create this configuration in your Auto Scaling group, EC2 Fleet, or Spot Fleet. Instead, you must manually set the instance weighting by using the WeightedCapacity parameter.

  • Use the capacity-optimized allocation strategy – Any score assumes that your fleet request will be configured to use all Availability Zones (for requesting capacity across Regions) or a single Availability Zone (if requesting capacity in one Availability Zone) and the capacity-optimized Spot allocation strategy for your request for Spot capacity to succeed. If you use other allocation strategies, such as lowest-price, the likelihood of getting available Spot capacity will not align with the score.

  • Act on a score immediately – The Spot placement score recommendation reflects the available Spot capacity at the time of the request, and the same configuration can yield different scores when calculated at different times due to Spot capacity fluctuations. While a score of 10 means that your Spot capacity request is highly likely—but not guaranteed—to succeed, for best results we recommend that you act on a score immediately. We also recommend that you get a fresh score each time you attempt a capacity request.