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5.3.2. Compute Cost Optimization (Purchasing Options, Right-Sizing)

šŸ’” First Principle: Optimizing compute costs involves strategically selecting EC2 purchasing options and continuously right-sizing instances to align resource capacity precisely with workload demand.

Scenario: You manage a batch processing application that can tolerate interruptions, and a core web application with a stable 24/7 load. You need to reduce compute costs for both.

Compute resources (primarily EC2 instances) often represent the largest portion of an AWS bill. SysOps Administrators must employ various strategies to optimize these costs.

Key Strategies for Compute Cost Optimization:
  • Right-Sizing: (Continuously evaluating compute instance types and sizes to ensure they are appropriately matched to workload requirements.)
    • Process: Monitor EC2 instance CPU utilization, memory (via CloudWatch Agent), and network I/O. Use AWS Compute Optimizer for recommendations.
    • Goal: Avoid over-provisioning (paying for unused capacity) or under-provisioning (leading to performance bottlenecks).
  • EC2 Purchasing Options:
    • On-Demand Instances: Pay by the second/hour. For unpredictable, short-term workloads.
    • Spot Instances: (Leverage unused EC2 capacity for up to 90% savings.) Ideal for fault-tolerant, flexible, and interruption-tolerant workloads (e.g., batch jobs, testing).
    • Reserved Instances (RIs): (Commit to a specific amount of compute capacity for 1 or 3 years for significant discounts.) For steady-state, predictable workloads.
    • Savings Plans: (A flexible pricing model offering discounts for a 1 or 3-year commitment to a consistent amount of compute usage, measured in $/hour.) Provides flexibility across EC2, Fargate, and Lambda usage.

āš ļø Common Pitfall: Not utilizing cost-saving purchasing options (RIs, Savings Plans, Spot) for predictable or fault-tolerant workloads, leading to higher On-Demand costs.

Key Trade-Offs: Cost savings (Spot, RIs, Savings Plans) versus flexibility and predictability (On-Demand).

Reflection Question: How does strategically selecting EC2 purchasing options (Spot Instances for batch, Savings Plans for web) and continuously right-sizing instances fundamentally optimize compute costs by aligning resource capacity with workload demand?