How To Use Spot Instances in AWS

Amazon Web Services (AWS) Spot Instances allow you to access spare Amazon Elastic Compute Cloud (EC2) capacity at significantly reduced rates—often up to 90% off the standard On-Demand prices. Spot Instances are ideal for flexible workloads, such as batch processing, big data, containerized applications, CI/CD, and any workload that can tolerate potential interruptions.

This guide walks you through setting up and managing Spot Instances in AWS, along with best practices to maximize their benefits.

Benefits of Using Spot Instances

Using Spot Instances can provide several key advantages:

• Cost Savings: Save up to 90% on EC2 costs compared to On-Demand instances.
• Scalability: Leverage spare capacity to scale out your applications cost-effectively.
• Flexibility for Interruption-Tolerant Applications: Spot Instances are ideal for stateless, fault-tolerant, or flexible applications that can withstand interruptions.

Step-by-Step Guide to Using AWS Spot Instances

Step 1: Identify Suitable Workloads for Spot Instances

Spot Instances are best suited for workloads that can tolerate interruptions. Examples of suitable workloads include:

• Batch processing (data analytics, image rendering, etc.)
• Big data and analytics
• Machine learning and training models
• Containerized applications
• CI/CD pipelines

Avoid using Spot Instances for applications that require high availability or are sensitive to interruptions, such as production databases or stateful applications unless they’re configured with redundancy and fault tolerance.

Step 2: Launch Spot Instances via the AWS Management Console

You can launch Spot Instances using the AWS Management Console. Follow these steps:

1. Open EC2 Console: In the AWS Management Console, navigate to EC2.
2. Select Launch Instance: Click Launch Instance.
3. Choose AMI and Instance Type: Select your Amazon Machine Image (AMI) and choose an instance type that fits your workload.
4. Choose Purchase Option:
   • In the Configure Instance section, under Request Spot Instances, select Request Spot Instances.
   • Set a Maximum Price if desired, or let AWS automatically set the price based on current availability.
5. Configure Interruption Behavior: Choose how the instance should behave if it’s interrupted.
   • Stop: The instance will stop and can be restarted when capacity is available.
   • Terminate: The instance will be terminated upon interruption.
6. Review and Launch: Configure other settings as needed (network, storage, tags), review your configuration, and click Launch.

Step 3: Use Spot Fleet to Manage Multiple Spot Instances

A Spot Fleet is a collection of Spot Instances and, optionally, On-Demand instances. Spot Fleets let you specify instance type diversification and automatically manage capacity for cost-effectiveness and availability.

1. Navigate to Spot Fleets: In the EC2 dashboard, click Spot Requests > Create Spot Fleet Request.
2. Specify Fleet Configuration:
   • Choose instance types, regions, and availability zones for a diversified fleet.
   • Set Target Capacity (number of instances or vCPU/Memory) and Maximum Price per instance.
3. Set Allocation Strategy:
   • Lowest Price: Prioritizes the lowest-cost instance pools.
   • Capacity Optimized: Prioritizes instance types with the most available Spot capacity.
4. Enable Instance Interruption Behavior:
   • Define how the Spot Fleet should respond to interruptions (Stop, Hibernate, Terminate).
5. Launch Spot Fleet: Review your configuration and click Request Spot Fleet.

AWS automatically provisions and manages instances within the specified fleet parameters, automatically replacing interrupted instances.

Step 4: Use Spot Instances with Auto Scaling

You can also configure Auto Scaling groups to include Spot Instances. This setup helps maintain instance counts based on demand while keeping costs down.

1. Open the Auto Scaling Console: Go to Auto Scaling Groups in the EC2 console.
2. Create or Edit an Auto Scaling Group:
   • Select your Launch Template or Launch Configuration.
   • Choose Mixed Instances Policy under Instance Purchasing Options.
3. Configure Mixed Instances:
   • Define a combination of On-Demand and Spot Instances based on your application requirements.
   • Set a percentage or instance count for Spot Instances.
4. Set Allocation Strategy: Select Capacity Optimized to increase Spot Instance availability by choosing instance types with the most capacity.
5. Add Scaling Policies: Configure scaling policies based on load metrics to add or remove instances automatically.

Auto Scaling groups can automatically replace Spot Instances that are interrupted, keeping your application up and running with minimal downtime.

Step 5: Manage Spot Instance Interruption Notifications

AWS provides a two-minute notification before a Spot Instance is terminated due to a lack of available capacity or price increases. You can use these notifications to gracefully handle interruptions.

1. Set Up Interruption Notifications:
   • Interruption notices are sent to the instance’s EC2 Instance Metadata service.
   • Access these notices by querying the metadata endpoint from within the instance:perlCopy codehttp://169.254.169.254/latest/meta-data/spot/termination-time
2. Handle Interruption Gracefully:
   • Set up a script within your instance to monitor this endpoint and initiate shutdown or data backup procedures if a termination notice is received.
   • For example, save the application state, move data to persistent storage, or detach and reattach storage volumes.

Step 6: Monitor and Optimize Spot Instance Usage

Monitor your Spot Instance usage regularly to ensure optimal performance and cost-effectiveness.

1. Use AWS Cost Explorer:
   • Open Cost Explorer in the Billing and Cost Management console to track Spot Instance spending.
   • Use the filters to view Spot Instance usage and identify cost-saving opportunities.
2. Track Spot Fleet Metrics in CloudWatch:
   • AWS CloudWatch provides metrics such as Spot Fleet Requests, Capacity Metrics, and Interruption Counts to monitor fleet health and manage Spot Instance usage.
3. Optimize Allocation Strategy: Adjust Spot Fleet and Auto Scaling configuration based on demand, workload requirements, and availability trends.

Best Practices for Using Spot Instances

1. Diversify Instance Types: Increase availability and minimize interruptions by using multiple instance types across different availability zones.
2. Use Spot Instances with On-Demand Instances: In production environments, consider a blend of Spot and On-Demand Instances to balance cost savings with availability.
3. Implement Interruption Handling: Use the interruption notice to ensure your application gracefully handles instance interruptions.
4. Use Spot Instances in Stateless Architectures: For best results, use Spot Instances in stateless applications, containerized workloads, or distributed systems where interruptions are less disruptive.
5. Leverage AWS Spot Advisor: AWS Spot Advisor recommends instance types with higher availability and lower interruption rates, helping you choose the most reliable Spot Instances.

Frequently Asked Questions Related to Using AWS Spot Instances