AWS r8idn.2xlargevsAWS r8idn.4xlarge

r8idn.2xlarge pairs 8 vCPUs with 64GB of RAM at $0.9379/hr On-Demand (about $675/mo at 24×7). r8idn.4xlarge pairs 16 vCPUs with 128GB at $1.8758/hr (~$1351/mo). r8idn.2xlarge is 100% cheaper per hour than r8idn.4xlarge ($0.9379/hr gap).

Because both instances are in the **r8idn 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: r8idn.2xlarge gives you 8 vCPUs and 64GB of RAM, r8idn.4xlarge gives you 16 vCPUs and 128GB. 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 r8idn.2xlarge delivers ~99% more single-thread Sysbench score per dollar (3571 vs 1790 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 (14121 vs 28288) are what to weigh. Spot pricing flips many of these comparisons — when r8idn.2xlarge drops to $0.3822/hr and r8idn.4xlarge drops to $0.8657/hr, the cheap-per-hour winner can swing meaningfully.

In practice, pick r8idn.2xlarge when your workload is closer to memory-optimized (memory-bound work — in-memory databases, real-time analytics, large caches). Pick r8idn.4xlarge 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.