AWS r8i.16xlargevsAWS r8i-flex.16xlarge

r8i.16xlarge pairs 64 vCPUs with 512GB of RAM at $4.4454/hr On-Demand (about $3201/mo at 24×7). r8i-flex.16xlarge pairs 64 vCPUs with 512GB at $4.2230/hr (~$3041/mo). r8i-flex.16xlarge is 5% cheaper per hour than r8i.16xlarge ($0.2224/hr gap).

r8i.16xlarge (memory-optimized, Intel Xeon (x86_64)) and r8i-flex.16xlarge (memory-optimized, Intel Xeon (x86_64)) target different workload shapes. The vCPU:RAM ratios are different (64:512 vs 64:512), and depending on the architectures involved you may also see meaningful single-thread performance and per-hour-cost differences. This kind of cross-category comparison is most useful when you're early in the design phase and not yet sure whether your workload is CPU-bound, memory-bound, or balanced — once that's clear, the right pick is usually obvious.

Benchmark data for at least one of these instances is still being collected, so a direct performance-per-dollar comparison isn't possible yet. Sysbench scores are pending for r8i.16xlarge and 3336/112300 for r8i-flex.16xlarge. Check back as the benchmark queue completes — newer-generation instances typically score 10–30% higher on single-thread and 15–50% higher on multi-core vs the previous generation in the same series.

In practice, pick r8i.16xlarge when your workload is closer to memory-optimized (memory-bound work — in-memory databases, real-time analytics, large caches). Pick r8i-flex.16xlarge 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.