Struct VmSpec 

pub struct VmSpec {
    pub kernel: Option<PathBuf>,
    pub rootfs: Option<PathBuf>,
    pub rootfs_read_only: Option<bool>,
    pub vcpu_count: Option<u8>,
    pub mem_size_mib: Option<u32>,
    pub boot_args: Option<String>,
    pub rootfs_rate_limit: Option<RateLimiter>,
    pub network_interfaces: Vec<NetworkInterface>,
    pub restore_from: Option<SnapshotRef>,
    pub track_dirty_pages: Option<bool>,
}

Per-VM configuration override. Every field is optional; None falls back to the provider’s workspace-level default (e.g. FirecrackerConfig).

Use VmSpec::default for cold boot with workspace defaults, or set VmSpec::restore_from to restore from a snapshot instead of cold-booting.

To do a warm-pool handoff — a pre-restored VM that swaps its TAP and IP onto a new tenant — set VmSpec::restore_from with SnapshotRef::network_overrides populated. Firecracker 1.10+ supports this; 1.6 rejects it.

Fields

kernel: Option<PathBuf>

Kernel image path. None = use workspace default.

rootfs: Option<PathBuf>

Rootfs image path. None = use workspace default.

rootfs_read_only: Option<bool>

Mount rootfs read-only. None = use workspace default.

vcpu_count: Option<u8>

vCPU count override.

mem_size_mib: Option<u32>

Memory size in MiB override.

boot_args: Option<String>

Kernel command-line override.

rootfs_rate_limit: Option<RateLimiter>

Rate limit applied to the rootfs drive.

network_interfaces: Vec<NetworkInterface>

Network interfaces to attach pre-boot. Firecracker requires these to be configured before InstanceStart. Empty by default — the VM has no network unless explicitly set.

restore_from: Option<SnapshotRef>

If set, the VM boots from a snapshot via PUT /snapshot/load instead of cold-booting. The spec’s kernel, rootfs, vcpu_count, mem_size_mib, boot_args, and network_interfaces are ignored when restoring (the snapshot encodes its own machine config). Use SnapshotRef::network_overrides to swap network interfaces on restore.

track_dirty_pages: Option<bool>

Track dirty pages during execution — required to later capture diff snapshots. None = enabled (FC’s safer default for snapshot-friendly workloads).

Trait Implementations

impl Clone for VmSpec

fn clone(&self) -> VmSpec

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for VmSpec

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for VmSpec

fn default() -> VmSpec

Returns the “default value” for a type.