A company runs big-data analytics and massively parallel processing on AWS test and development servers and can tolerate occasional interruptions. Which EC2 purchasing option is the most cost-effective?

Spot Instances are the most cost-effective option for workloads that can tolerate interruptions, such as big-data analytics and massively parallel processing on test/development servers. They allow you to bid on unused EC2 capacity, offering significant discounts compared to On-Demand prices. The trade-off is that AWS can reclaim these instances with short notice if the capacity is needed elsewhere. On-Demand Instances are suitable for short-term, irregular workloads where you can't commit to a longer term, but they are more expensive than Spot Instances. Reserved Instances are for steady-state workloads with predictable usage over a 1- or 3-year term, offering significant discounts but requiring a commitment. Savings Plans also offer discounts in exchange for a commitment to a consistent amount of compute usage (measured in $/hour) over 1 or 3 years, but they are not designed for interruptible workloads.