The m6g.xlarge pairs 4 vCPU with 16 GiB of RAM, the 4.00 GiB-per-vCPU ratio that marks a general-purpose instance. In the name, "m" is the general-purpose line, "6" is the generation, "g" marks AWS Graviton (ARM) processors and "xlarge" is the size within the m6g family. It runs on AWS Graviton2 Processor at 2.5 GHz, and AWS introduced it in May 2020. AWS has since shipped m7g, m8g and m9g; m7g.xlarge is the direct replacement at this size, scoring 103,066 CoreMark/s against this instance's 77,002 — roughly 34% more throughput for the same vCPU count. gp.vs2.large on Rackspace Spot lines up one-for-one: 4 vCPU and 16 GiB, about 93% below the US East (N. Virginia) on-demand rate.
Match qualityx86 substitution
m6g.xlarge is Graviton (arm64). Rackspace Spot does not have arm64 servers, so gp.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.
