The c6g.4xlarge pairs 16 vCPU with 32 GiB of RAM, the 2.00 GiB-per-vCPU ratio that marks a compute-optimized instance. In the name, "c" stands for compute, "6" is the generation, "g" marks AWS Graviton (ARM) processors and "4xlarge" is the size within the c6g family. It runs on AWS Graviton2 Processor at 2.5 GHz, and AWS introduced it in June 2020. AWS has since shipped c7g, c8g and c9g; c7g.4xlarge is the direct replacement at this size, scoring 413,330 CoreMark/s against this instance's 321,737 — roughly 28% more throughput for the same vCPU count. ch.vs1.2xlarge on Rackspace Spot lines up one-for-one: 16 vCPU and 32 GiB, about 92% below the US East (N. Virginia) on-demand rate.
Match qualityx86 substitution
c6g.4xlarge is Graviton (arm64). Rackspace Spot does not have arm64 servers, so ch.vs1.2xlarge 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.
