Use a Firecracker custom CPU template to homogenize a heterogeneous fleet so all guests see an identical CPU feature set

Documented steps

1. Audit the union of CPU features across all host CPU models in your fleet (Intel/AMD mixes allowed at the instruction-set level if you avoid cross-vendor CPUID representation)
2. Pick the lowest common denominator of features you want every guest to see, then encode that as CPUID/MSR modifiers in a custom template JSON
3. Apply the same template on every host via PUT /cpu-config (x86_64) before InstanceStart, ensuring identical guest-visible CPUID
4. For cross-vendor Intel+AMD instruction-set parity, use the T2CL template on Intel hosts and T2A on AMD hosts (these two are designed to give feature parity for Hetzner-style heterogeneous fleets)
5. Test on each distinct host model and compare guest /proc/cpuinfo output to confirm uniformity
6. Keep the template JSON under version control (e.g. in the repo along with the snapshot/kernel artifacts)