AWS r8i.2xlargevsAWS r8i-flex.xlarge

r8i.2xlarge pairs 8 vCPUs with 64GB of RAM at $0.5557/hr On-Demand (about $400/mo at 24×7). r8i-flex.xlarge pairs 4 vCPUs with 32GB at $0.2639/hr (~$190/mo). r8i-flex.xlarge is 53% cheaper per hour than r8i.2xlarge ($0.2917/hr gap).

Because both instances are in the **r8i family**, the only thing that changes between them is sizing — same silicon, same architecture (Intel Xeon (x86_64)), same burstable/sustained behavior. The choice is purely about how much capacity you actually need: r8i.2xlarge gives you 8 vCPUs and 64GB of RAM, r8i-flex.xlarge gives you 4 vCPUs and 32GB. AWS scales pricing close to linearly within a family, so picking the right size is mostly about right-sizing your workload, not getting a better deal per vCPU.

On raw price-per-performance, the two are r8i-flex.xlarge delivers ~111% more single-thread Sysbench score per dollar (5984 vs 12628 points per $1/hr). That's the cleanest signal we have for "which one runs your workload faster per dollar," but it only matters if your workload is single-thread-bound; for parallel workloads the multi-core scores (13992 vs 6992) are what to weigh. Spot pricing flips many of these comparisons — when r8i.2xlarge drops to $0.2508/hr and r8i-flex.xlarge drops to $0.1198/hr, the cheap-per-hour winner can swing meaningfully.

In practice, pick r8i.2xlarge when your workload is closer to memory-optimized (memory-bound work — in-memory databases, real-time analytics, large caches). Pick r8i-flex.xlarge when it's closer to memory-optimized (memory-bound work — in-memory databases, real-time analytics, large caches). When neither side is obviously right, the cheaper hourly rate usually wins for fault-tolerant batch workloads, while the higher single-core score usually wins for latency-sensitive web traffic. The regional pricing tables linked from each instance page below show where each is currently cheapest — sometimes a >20% regional gap flips the comparison entirely.