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Managing Spot Instances with Auto Scaling
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You can take advantage of Auto Scaling features to manage your Amazon EC2 Spot Instances. With Auto Scaling, you can scale up or down your capacity based on demand by setting up Auto Scaling to make Spot bids on your behalf.
In addition, you can use Auto Scaling's scheduling functionality for more granular control over when to bid and launch your Spot Instances. You also can use an Amazon Simple Notification Service (Amazon SNS)-backed Auto Scaling feature that sends notifications each time specified events—such as the launch or termination of instances—take place. Using Auto Scaling's scheduled actions, you can set up bids to expire at a set time.
When you use Auto Scaling with Spot Instances, there are some Auto Scaling tools that you have to use instead of the Spot Instance tools that might be familiar. There are also a number of Spot Instance options that you cannot use. Here's a summary of differences:
Setting your bid price. When you use Auto Scaling to launch Spot Instances, you set your bid price in an Auto Scaling launch configuration.
Spot market price and your bid price. This is the same as current behavior. If the market price for Spot Instances rises above your bid price for a running instance, Amazon EC2 will terminate your instance.
Changing your bid price. If you want to change your bid price, you have to create a new launch configuration and associate it with your Auto Scaling group. You cannot update the existing launch configuration.
New bid price and running instances. When you change your bid price by creating a new launch configuration, instances already launched will continue to run as long as the bid price for those running instances is higher than the current market price for Spot Instances.
Spot and Auto Scaling instance termination. Amazon EC2 terminates a Spot Instance when the bid price for that instance falls below the Spot market price. Auto Scaling terminates instances based on a combination of criteria, including the launch configuration it is associated with, length of time in a billing hour the instance has been running, and the Availability Zone in which it is launched. For more information about instance termination in Auto Scaling, see Auto Scaling Instance Termination.
Maintaining your Spot Instances. When your instance is terminated, Auto Scaling will try to launch another instance to replace it in order to maintain your specified desired capacity. However, whether or not Auto Scaling successfully launches an instance depends on the bid price as compared to the Spot market price: If the bid price is higher than the Spot market price, then an instance will be launched; if the Spot market price is higher than the bid price, then no instance will be launched at that point.
Persistent bids. Auto Scaling will continue submitting bids for you as long as you keep your Auto Scaling group and launch configuration. The Auto Scaling group specifies the desired number of instances you want maintained and the launch configuration specifies the bid price for your Spot Instances.
For more information about Auto Scaling, see Auto Scaling Developer Guide. To get started quickly with Auto Scaling, see Get Started with Auto Scaling.
