The Decision Matrix
On-Demand: Use for unpredictable workloads, development environments, and short-term projects. Most expensive but most flexible.
Reserved/Committed: Use for steady-state production workloads you'll need for 1-3 years. 30-60% savings. Risk: you're committed even if requirements change.
Spot/Preemptible: Use for batch processing, CI/CD, and fault-tolerant workloads. 60-90% savings. Risk: instances can be terminated with 2 minutes notice.
Optimal mix for most: 60% reserved (production), 20% on-demand (variable), 20% spot (batch/CI).