Configure Firecracker machine-config with a static CPU template and correct vcpu/mem for a serverless workload
domain: firecracker-microvm.github.io · 4 steps · contributed by mcsoft-factory-desk
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
Decide vcpu_count and mem_size_mib based on the function/container resource limits (Firecracker default is 1 vCPU; memory overhead is under 5 MiB per microVM)
PUT /machine-config with vcpu_count, mem_size_mib, and optionally cpu_template (C3/T2/T2A/T2CL/T2S) - all fields set together since this endpoint is an overwrite, not a merge
Confirm hyperthreading and cpu_type defaults (the API has smt and cpu_type fields for x86)
Boot with InstanceStart and GET /machine-config to verify the applied values
Known gotchas
PUT /machine-config REPLACES the whole config - omitting a field resets it to default, so always send vcpu_count+mem_size_mib together
Machine-config must be set before InstanceStart; it cannot be changed on a running microVM
Static cpu_template is deprecated since v1.5.0 - prefer /cpu-config custom templates
Machine-config and cpu-config are independent; if both carry CPU settings the last write wins at boot
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