The r7g.16xlarge is a memory-optimized AWS EC2 instance: 64 vCPU and 512 GiB of memory, 8.00 GiB per vCPU. In the name, "r" stands for RAM, "7" is the generation, "g" marks AWS Graviton (ARM) processors and "16xlarge" is the size within the r7g family. It runs on AWS Graviton3 Processor at 2.5 GHz, and AWS introduced it in February 2023. AWS has since shipped r8g and r9g; r8g.16xlarge is the direct replacement at this size, scoring 2,040,491 CoreMark/s against this instance's 1,652,572 — roughly 23% more throughput for the same vCPU count. No single Spot node covers 64 vCPU and 512 GiB, so the equivalent is a fleet: 4 × mh.vs1.2xlarge, 64 vCPU and 512 GiB in total, $3.43/hr on AWS in US East (N. Virginia), from $0.084/hr on Rackspace Spot. Spot delivers compute as managed Kubernetes, so a node pool of that size is the native shape of the answer rather than a workaround — provided the workload scales horizontally.
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r7g.16xlarge gives you 64 vCPU and 512 GiB in a single machine. The largest comparable Spot node, mh.vs1.2xlarge, is 16 vCPU and 128 GiB, so the equivalent here is 4 nodes rather than one.
Spot runs as managed Kubernetes, so a 4-node pool is the normal way to run things rather than a workaround. If your workload already sits behind a load balancer, a queue or a scheduler, it spreads across them without changes. If it needs all 64 cores and 512 GiB in one process, it does not.
x86_64 onlyr7g.16xlarge is Graviton (arm64) and Rackspace Spot has no arm64 nodes, so you'd be moving to x86. You'll need x86 builds of your images, and per-core speed differs between the chips — worth testing before you decide how many nodes to run.
