AWS Fargate Spot: Cost optimization with managed container workloads

Before diving into the details, let's clarify the terminology used throughout this article. AWS Fargate (or regular Fargate) refers to AWS's serverless compute engine for containers with standard on-demand pricing. AWS Fargate Spot (or simply Fargate Spot) is the spot pricing version that offers the same compute service at a discounted rate. You might also see these referred to as Fargate On-Demand vs Fargate Spot, or standard Fargate vs spot Fargate. Regardless of the terminology, they represent the same concept: the choice between predictable, always-available capacity and potentially interruptible but more cost-effective capacity.

In the ever-evolving landscape of cloud computing, cost optimization remains a crucial consideration for organizations of all sizes. AWS Fargate Spot offers a compelling solution for running containerized applications at a significantly reduced cost compared to regular Fargate pricing. Let's dive deep into what makes Fargate Spot an attractive option and understand its trade-offs.

Cost Benefits

As of January 2025, the cost savings with Fargate Spot in the eu-west-1 region are substantial:

• Regular Fargate: $32.34/month for 1 vCPU, 1GB container
• Fargate Spot: $9.96/month for the same configuration
• Total savings: Approximately 69%

These savings can significantly impact your cloud budget, especially when running multiple containers or scaling your applications.

Understanding the Trade-offs

Instance Reclamation

The primary consideration when using Fargate Spot is the possibility of instance reclamation. Here are the key points:

1. AWS can reclaim the capacity with a maximum of 2 minutes notice
2. You receive a SIGTERM signal that allows for graceful shutdown
3. The stopTimeout can be configured in your task definition (up to 2 minutes)

For applications running PHP, you can implement signal handling using the pcntl_signal function to manage cleanup operations:

pcntl_signal(SIGTERM, function($signo) {
    // Perform cleanup operations
    // Save state, close connections, etc.
});

Availability Considerations

Spot capacity availability varies by region and Availability Zone (AZ). Some important observations:

1. Capacity unavailability is typically limited to specific AZs
2. Multi-AZ deployments significantly reduce the impact of capacity constraints
3. Current instance longevity can vary:
   • Some containers run continuously for extended periods (15+ days observed)
   • Others might be reclaimed more frequently
   • Reclamation frequency varies by region and AZ

Best Practices and Strategies

Mixed Capacity Providers

One effective strategy is to combine different capacity providers:

1. Use regular Fargate for baseline, stable workloads
2. Leverage Fargate Spot for scaling out during peak periods
3. This hybrid approach balances reliability with cost optimization

Cost Comparison with EC2

When deciding between Fargate and EC2 for container hosting, consider these comparisons:

c5.xlarge (4 vCPU, 8GB RAM)

• EC2 On-demand: $0.17/hour
• Fargate equivalent: $0.19748/hour
• Fargate premium: ~16%

m5.xlarge (4 vCPU, 16GB RAM)

• EC2 On-demand: $0.192/hour
• Fargate equivalent: $0.23304/hour
• Fargate premium: ~21%

t3.xlarge (4 vCPU, 16GB RAM)

• EC2 On-demand: $0.1664/hour
• Fargate equivalent: $0.23304/hour
• Fargate premium: ~40%

The decision between Fargate and EC2 depends largely on:

• Cluster utilization rates
• Operational overhead
• Total Cost of Ownership (TCO) considerations including:
  • Patching requirements
  • Scaling operations
  • Cluster maintenance
  • Team expertise and time investment

Conclusion

AWS Fargate Spot offers significant cost savings for container workloads that can handle occasional interruptions. While it requires careful consideration of application architecture and resilience, the potential 69% cost reduction makes it an attractive option for many use cases. By implementing proper handling of termination signals and using multi-AZ deployments, organizations can effectively mitigate the main drawbacks while taking advantage of the cost benefits.

For optimal results, consider implementing a hybrid approach using both regular Fargate and Fargate Spot, and carefully evaluate your specific use case against the EC2 alternatives when making architectural decisions.