r6g.xlarge is AWS's memory-optimized EC2 size at 4 vCPU and 32 GiB. In the name, "r" stands for RAM, "6" is the generation, "g" marks AWS Graviton (ARM) processors and "xlarge" is the size within the r6g family. It runs on AWS Graviton2 Processor at 2.5 GHz, and AWS introduced it in June 2020. AWS has since shipped r7g, r8g and r9g; r7g.xlarge is the direct replacement at this size, scoring 102,571 CoreMark/s against this instance's 79,507 — roughly 29% more throughput for the same vCPU count. On Rackspace Spot the same shape is mh.vs2.large — 4 vCPU, 32 GiB, matched on both dimensions, about 90% below the US East (N. Virginia) on-demand rate.
Match qualityx86 substitution
r6g.xlarge is Graviton (arm64). Rackspace Spot does not have arm64 servers, so mh.vs2.large is an x86_64 substitute with similar specs.
You will need x86 builds of your container images. Most software rebuilds without changes, but anything with compiled native code needs a real rebuild rather than a retag. Speed per core also differs between the two chips, so it is worth testing before deciding how many nodes to run.