Understanding EC2 Spot Instances, Spot Blocks, and Spot Fleets

Introduction

Amazon Web Services (AWS) offers a variety of instance types for their Elastic Compute Cloud (EC2), but understanding the cost-efficient options like Spot Instances, Spot Blocks, and Spot Fleets can be challenging. This blog post aims to demystify these concepts, helping you to decide when and how to use them effectively.

EC2 Spot Instances

Spot Instances are an AWS offering that allows users to purchase unused EC2 capacity at a significantly reduced price - up to 90% cheaper than On-Demand prices. However, these instances come with a catch:

• Availability: Your Spot Instance can be terminated at any moment if the market price exceeds your bid price.
• Cost-Efficiency: These are the most cost-effective instances available on AWS.
• Best Use Cases: They are ideal for tasks that can tolerate interruptions, such as batch processing, data analysis, image processing, and other non-critical distributed workloads.
• Flexibility: Spot Instances are great for jobs with flexible start and end times.
• Not Ideal For: They are not recommended for critical jobs or databases due to their unpredictability.

EC2 Spot Instance Requests

When you request a Spot Instance, you specify the maximum price you're willing to pay. If the current spot price is lower than your bid, you get the instance. If it goes higher, you can choose to stop or terminate your instance, with a 2-minute notification.

• Spot Blocks: A variation where you can reserve a Spot Instance for a specified time frame (1-6 hours), reducing the chance of interruption. However, they can still be reclaimed by AWS in rare cases.
• Use Cases: Similar to Spot Instances, Spot Blocks are suitable for batch jobs and resilient workloads but not for critical applications.

How to Terminate Spot Instances?

Terminating a Spot Instance involves two steps:

1. Cancel the Spot Instance request (if it's open, active, or disabled).
2. Then terminate the associated Spot Instances.

Spot Fleets

A Spot Fleet is a collection of Spot Instances and, optionally, On-Demand Instances. It automates the process of requesting and managing multiple Spot Instances to meet certain criteria.

• Target Capacity and Price Constraints: You define the desired capacity and the price constraints for the fleet.
• Launch Pools: You can specify multiple launch pools (instance types, OS, Availability Zones), allowing the fleet to choose the best option based on your criteria.
• Strategies for Allocating Spot Instances:
  • LowestPrice: The fleet selects instances from the pool with the lowest cost, ideal for short workloads and cost optimization.
  • Diversified: Distributes instances across all pools, enhancing availability, suitable for longer workloads.
  • CapacityOptimized: Chooses the pool with optimal capacity for the number of instances you need.
  • PriceCapacityOptimized: Combines capacity optimization with cost-effectiveness, generally the best choice for a wide range of workloads.
• Automatic Management: The Spot Fleet handles the request and management of Spot Instances, ensuring the lowest price under your constraints.

Conclusion

Spot Instances, Spot Blocks, and Spot Fleets offer cost-effective solutions for utilizing AWS's EC2 service. While they are perfect for flexible, non-critical workloads, they're not suitable for jobs requiring high availability. Understanding these options can lead to significant cost savings and efficient resource utilization in your cloud infrastructure.