Refactor VM lifecycle around capabilities

Make host-integrated VM features fit a standard Go extension path instead of adding more one-off branches through vm.go. This is the enabling refactor for future work like shared mounts, not the /work feature itself.

Add a daemon capability pipeline plus a structured guest-config builder, then move the existing /root work-disk mount, built-in DNS, and NAT wiring onto those hooks. Generalize Firecracker drive config at the same time so later storage features can extend machine setup without another hardcoded path.

Add banger doctor on top of the shared readiness checks, update the docs to describe the new architecture, and cover the new seams with guest-config, capability, report, CLI, and full go test verification. Also verify make build and a real ./banger doctor run on the host.

internal/daemon/capabilities.go

@@ -0,0 +1,272 @@
+package daemon
+
+import (
+	"context"
+	"errors"
+	"net"
+	"strings"
+
+	"banger/internal/firecracker"
+	"banger/internal/guestconfig"
+	"banger/internal/model"
+	"banger/internal/system"
+	"banger/internal/vmdns"
+)
+
+type vmCapability interface {
+	Name() string
+}
+
+type startPreflightCapability interface {
+	AddStartPreflight(context.Context, *Daemon, *system.Preflight, model.VMRecord, model.Image)
+}
+
+type guestConfigCapability interface {
+	ContributeGuest(*guestconfig.Builder, model.VMRecord, model.Image)
+}
+
+type machineConfigCapability interface {
+	ContributeMachine(*firecracker.MachineConfig, model.VMRecord, model.Image)
+}
+
+type prepareHostCapability interface {
+	PrepareHost(context.Context, *Daemon, *model.VMRecord, model.Image) error
+}
+
+type postStartCapability interface {
+	PostStart(context.Context, *Daemon, model.VMRecord, model.Image) error
+}
+
+type cleanupCapability interface {
+	Cleanup(context.Context, *Daemon, model.VMRecord) error
+}
+
+type configChangeCapability interface {
+	ApplyConfigChange(context.Context, *Daemon, model.VMRecord, model.VMRecord) error
+}
+
+type doctorCapability interface {
+	AddDoctorChecks(context.Context, *Daemon, *system.Report)
+}
+
+func (d *Daemon) registeredCapabilities() []vmCapability {
+	if len(d.vmCaps) > 0 {
+		return d.vmCaps
+	}
+	return []vmCapability{
+		workDiskCapability{},
+		dnsCapability{},
+		natCapability{},
+	}
+}
+
+func (d *Daemon) addCapabilityStartPrereqs(ctx context.Context, checks *system.Preflight, vm model.VMRecord, image model.Image) {
+	for _, capability := range d.registeredCapabilities() {
+		if hook, ok := capability.(startPreflightCapability); ok {
+			hook.AddStartPreflight(ctx, d, checks, vm, image)
+		}
+	}
+}
+
+func (d *Daemon) contributeGuestConfig(builder *guestconfig.Builder, vm model.VMRecord, image model.Image) {
+	for _, capability := range d.registeredCapabilities() {
+		if hook, ok := capability.(guestConfigCapability); ok {
+			hook.ContributeGuest(builder, vm, image)
+		}
+	}
+}
+
+func (d *Daemon) contributeMachineConfig(cfg *firecracker.MachineConfig, vm model.VMRecord, image model.Image) {
+	for _, capability := range d.registeredCapabilities() {
+		if hook, ok := capability.(machineConfigCapability); ok {
+			hook.ContributeMachine(cfg, vm, image)
+		}
+	}
+}
+
+func (d *Daemon) prepareCapabilityHosts(ctx context.Context, vm *model.VMRecord, image model.Image) error {
+	prepared := make([]vmCapability, 0, len(d.registeredCapabilities()))
+	for _, capability := range d.registeredCapabilities() {
+		hook, ok := capability.(prepareHostCapability)
+		if !ok {
+			continue
+		}
+		if err := hook.PrepareHost(ctx, d, vm, image); err != nil {
+			d.cleanupPreparedCapabilities(context.Background(), vm, prepared)
+			return err
+		}
+		prepared = append(prepared, capability)
+	}
+	return nil
+}
+
+func (d *Daemon) postStartCapabilities(ctx context.Context, vm model.VMRecord, image model.Image) error {
+	for _, capability := range d.registeredCapabilities() {
+		if hook, ok := capability.(postStartCapability); ok {
+			if err := hook.PostStart(ctx, d, vm, image); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+func (d *Daemon) cleanupCapabilityState(ctx context.Context, vm model.VMRecord) error {
+	return d.cleanupPreparedCapabilities(ctx, &vm, d.registeredCapabilities())
+}
+
+func (d *Daemon) cleanupPreparedCapabilities(ctx context.Context, vm *model.VMRecord, capabilities []vmCapability) error {
+	var err error
+	for index := len(capabilities) - 1; index >= 0; index-- {
+		hook, ok := capabilities[index].(cleanupCapability)
+		if !ok {
+			continue
+		}
+		err = joinErr(err, hook.Cleanup(ctx, d, *vm))
+	}
+	return err
+}
+
+func (d *Daemon) applyCapabilityConfigChanges(ctx context.Context, before, after model.VMRecord) error {
+	for _, capability := range d.registeredCapabilities() {
+		if hook, ok := capability.(configChangeCapability); ok {
+			if err := hook.ApplyConfigChange(ctx, d, before, after); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+func (d *Daemon) addCapabilityDoctorChecks(ctx context.Context, report *system.Report) {
+	for _, capability := range d.registeredCapabilities() {
+		if hook, ok := capability.(doctorCapability); ok {
+			hook.AddDoctorChecks(ctx, d, report)
+		}
+	}
+}
+
+type workDiskCapability struct{}
+
+func (workDiskCapability) Name() string { return "work-disk" }
+
+func (workDiskCapability) AddStartPreflight(_ context.Context, _ *Daemon, checks *system.Preflight, vm model.VMRecord, _ model.Image) {
+	if exists(vm.Runtime.WorkDiskPath) {
+		return
+	}
+	for _, command := range []string{"mkfs.ext4", "mount", "umount", "cp"} {
+		checks.RequireCommand(command, toolHint(command))
+	}
+}
+
+func (workDiskCapability) ContributeGuest(builder *guestconfig.Builder, _ model.VMRecord, _ model.Image) {
+	builder.AddMount(guestconfig.MountSpec{
+		Source:  "/dev/vdb",
+		Target:  "/root",
+		FSType:  "ext4",
+		Options: []string{"defaults"},
+		Dump:    0,
+		Pass:    2,
+	})
+}
+
+func (workDiskCapability) ContributeMachine(cfg *firecracker.MachineConfig, vm model.VMRecord, _ model.Image) {
+	cfg.Drives = append(cfg.Drives, firecracker.DriveConfig{
+		ID:       "work",
+		Path:     vm.Runtime.WorkDiskPath,
+		ReadOnly: false,
+	})
+}
+
+func (workDiskCapability) PrepareHost(ctx context.Context, d *Daemon, vm *model.VMRecord, _ model.Image) error {
+	return d.ensureWorkDisk(ctx, vm)
+}
+
+func (workDiskCapability) AddDoctorChecks(_ context.Context, _ *Daemon, report *system.Report) {
+	checks := system.NewPreflight()
+	for _, command := range []string{"mkfs.ext4", "mount", "umount", "cp"} {
+		checks.RequireCommand(command, toolHint(command))
+	}
+	report.AddPreflight("feature /root work disk", checks, "guest /root work disk tooling available")
+}
+
+type dnsCapability struct{}
+
+func (dnsCapability) Name() string { return "dns" }
+
+func (dnsCapability) PostStart(ctx context.Context, d *Daemon, vm model.VMRecord, _ model.Image) error {
+	return d.setDNS(ctx, vm.Name, vm.Runtime.GuestIP)
+}
+
+func (dnsCapability) Cleanup(ctx context.Context, d *Daemon, vm model.VMRecord) error {
+	return d.removeDNS(ctx, vm.Runtime.DNSName)
+}
+
+func (dnsCapability) AddDoctorChecks(_ context.Context, _ *Daemon, report *system.Report) {
+	conn, err := net.ListenPacket("udp", vmdns.DefaultListenAddr)
+	if err != nil {
+		if strings.Contains(strings.ToLower(err.Error()), "address already in use") {
+			report.AddWarn("feature vm dns", "listener address "+vmdns.DefaultListenAddr+" is already in use")
+			return
+		}
+		report.AddFail("feature vm dns", "cannot bind "+vmdns.DefaultListenAddr+": "+err.Error())
+		return
+	}
+	_ = conn.Close()
+	report.AddPass("feature vm dns", "listener can bind "+vmdns.DefaultListenAddr)
+}
+
+type natCapability struct{}
+
+func (natCapability) Name() string { return "nat" }
+
+func (natCapability) AddStartPreflight(ctx context.Context, d *Daemon, checks *system.Preflight, vm model.VMRecord, _ model.Image) {
+	if !vm.Spec.NATEnabled {
+		return
+	}
+	d.addNATPrereqs(ctx, checks)
+}
+
+func (natCapability) PostStart(ctx context.Context, d *Daemon, vm model.VMRecord, _ model.Image) error {
+	if !vm.Spec.NATEnabled {
+		return nil
+	}
+	return d.ensureNAT(ctx, vm, true)
+}
+
+func (natCapability) Cleanup(ctx context.Context, d *Daemon, vm model.VMRecord) error {
+	if !vm.Spec.NATEnabled {
+		return nil
+	}
+	return d.ensureNAT(ctx, vm, false)
+}
+
+func (natCapability) ApplyConfigChange(ctx context.Context, d *Daemon, before, after model.VMRecord) error {
+	if before.Spec.NATEnabled == after.Spec.NATEnabled {
+		return nil
+	}
+	if after.State != model.VMStateRunning || !system.ProcessRunning(after.Runtime.PID, after.Runtime.APISockPath) {
+		return nil
+	}
+	return d.ensureNAT(ctx, after, after.Spec.NATEnabled)
+}
+
+func (natCapability) AddDoctorChecks(ctx context.Context, d *Daemon, report *system.Report) {
+	checks := system.NewPreflight()
+	checks.RequireCommand("ip", toolHint("ip"))
+	d.addNATPrereqs(ctx, checks)
+	if len(checks.Problems()) > 0 {
+		report.Add(system.CheckStatusFail, "feature nat", checks.Problems()...)
+		return
+	}
+	uplink, err := d.defaultUplink(ctx)
+	if err != nil {
+		report.AddFail("feature nat", err.Error())
+		return
+	}
+	report.AddPass("feature nat", "iptables/sysctl available, uplink "+uplink)
+}
+
+func joinErr(current, next error) error {
+	return errors.Join(current, next)
+}

internal/daemon/capabilities_test.go

@@ -0,0 +1,145 @@
+package daemon
+
+import (
+	"context"
+	"errors"
+	"reflect"
+	"testing"
+
+	"banger/internal/firecracker"
+	"banger/internal/guestconfig"
+	"banger/internal/model"
+	"banger/internal/system"
+)
+
+type testCapability struct {
+	name           string
+	prepare        func(context.Context, *Daemon, *model.VMRecord, model.Image) error
+	cleanup        func(context.Context, *Daemon, model.VMRecord) error
+	contribute     func(*guestconfig.Builder, model.VMRecord, model.Image)
+	contributeFC   func(*firecracker.MachineConfig, model.VMRecord, model.Image)
+	configChange   func(context.Context, *Daemon, model.VMRecord, model.VMRecord) error
+	doctor         func(context.Context, *Daemon, *system.Report)
+	startPreflight func(context.Context, *Daemon, *system.Preflight, model.VMRecord, model.Image)
+}
+
+func (c testCapability) Name() string { return c.name }
+
+func (c testCapability) PrepareHost(ctx context.Context, d *Daemon, vm *model.VMRecord, image model.Image) error {
+	if c.prepare != nil {
+		return c.prepare(ctx, d, vm, image)
+	}
+	return nil
+}
+
+func (c testCapability) Cleanup(ctx context.Context, d *Daemon, vm model.VMRecord) error {
+	if c.cleanup != nil {
+		return c.cleanup(ctx, d, vm)
+	}
+	return nil
+}
+
+func (c testCapability) ContributeGuest(builder *guestconfig.Builder, vm model.VMRecord, image model.Image) {
+	if c.contribute != nil {
+		c.contribute(builder, vm, image)
+	}
+}
+
+func (c testCapability) ContributeMachine(cfg *firecracker.MachineConfig, vm model.VMRecord, image model.Image) {
+	if c.contributeFC != nil {
+		c.contributeFC(cfg, vm, image)
+	}
+}
+
+func (c testCapability) ApplyConfigChange(ctx context.Context, d *Daemon, before, after model.VMRecord) error {
+	if c.configChange != nil {
+		return c.configChange(ctx, d, before, after)
+	}
+	return nil
+}
+
+func (c testCapability) AddDoctorChecks(ctx context.Context, d *Daemon, report *system.Report) {
+	if c.doctor != nil {
+		c.doctor(ctx, d, report)
+	}
+}
+
+func (c testCapability) AddStartPreflight(ctx context.Context, d *Daemon, checks *system.Preflight, vm model.VMRecord, image model.Image) {
+	if c.startPreflight != nil {
+		c.startPreflight(ctx, d, checks, vm, image)
+	}
+}
+
+func TestPrepareCapabilityHostsRollsBackPreparedCapabilitiesInReverseOrder(t *testing.T) {
+	vm := testVM("devbox", "image", "172.16.0.2")
+	var cleanupOrder []string
+
+	d := &Daemon{
+		vmCaps: []vmCapability{
+			testCapability{
+				name: "first",
+				prepare: func(context.Context, *Daemon, *model.VMRecord, model.Image) error {
+					return nil
+				},
+				cleanup: func(context.Context, *Daemon, model.VMRecord) error {
+					cleanupOrder = append(cleanupOrder, "first")
+					return nil
+				},
+			},
+			testCapability{
+				name: "second",
+				prepare: func(context.Context, *Daemon, *model.VMRecord, model.Image) error {
+					return nil
+				},
+				cleanup: func(context.Context, *Daemon, model.VMRecord) error {
+					cleanupOrder = append(cleanupOrder, "second")
+					return nil
+				},
+			},
+			testCapability{
+				name: "broken",
+				prepare: func(context.Context, *Daemon, *model.VMRecord, model.Image) error {
+					return errors.New("boom")
+				},
+			},
+		},
+	}
+
+	err := d.prepareCapabilityHosts(context.Background(), &vm, model.Image{})
+	if err == nil || err.Error() != "boom" {
+		t.Fatalf("prepareCapabilityHosts() error = %v, want boom", err)
+	}
+	if !reflect.DeepEqual(cleanupOrder, []string{"second", "first"}) {
+		t.Fatalf("cleanup order = %v, want reverse prepared order", cleanupOrder)
+	}
+}
+
+func TestContributeHooksPopulateGuestAndMachineConfig(t *testing.T) {
+	d := &Daemon{
+		vmCaps: []vmCapability{
+			testCapability{
+				name: "guest",
+				contribute: func(builder *guestconfig.Builder, _ model.VMRecord, _ model.Image) {
+					builder.AddMount(guestconfig.MountSpec{Source: "/dev/vdb", Target: "/work", FSType: "ext4"})
+				},
+				contributeFC: func(cfg *firecracker.MachineConfig, _ model.VMRecord, _ model.Image) {
+					cfg.Drives = append(cfg.Drives, firecracker.DriveConfig{ID: "work", Path: "/tmp/work.ext4"})
+				},
+			},
+		},
+	}
+
+	builder := guestconfig.NewBuilder()
+	d.contributeGuestConfig(builder, model.VMRecord{}, model.Image{})
+
+	cfg := firecracker.MachineConfig{Drives: []firecracker.DriveConfig{{ID: "rootfs", Path: "/dev/root", IsRoot: true}}}
+	d.contributeMachineConfig(&cfg, model.VMRecord{}, model.Image{})
+
+	fstab := builder.RenderFSTab("")
+	if !reflect.DeepEqual(cfg.Drives[1], firecracker.DriveConfig{ID: "work", Path: "/tmp/work.ext4"}) {
+		t.Fatalf("machine drives = %+v, want contributed work drive", cfg.Drives)
+	}
+	if want := "/dev/vdb /work ext4 defaults 0 0\n"; fstab != want {
+		t.Fatalf("guest fstab = %q, want %q", fstab, want)
+	}
+}

internal/daemon/daemon.go

@@ -39,6 +39,7 @@ type Daemon struct {
 	pid            int
 	listener       net.Listener
 	vmDNS          *vmdns.Server
+	vmCaps         []vmCapability
 	imageBuild     func(context.Context, imageBuildSpec) error
 	requestHandler func(context.Context, rpc.Request) rpc.Response
 }

internal/daemon/doctor.go

@@ -0,0 +1,92 @@
+package daemon
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"banger/internal/config"
+	"banger/internal/model"
+	"banger/internal/paths"
+	"banger/internal/system"
+)
+
+func Doctor(ctx context.Context) (system.Report, error) {
+	layout, err := paths.Resolve()
+	if err != nil {
+		return system.Report{}, err
+	}
+	cfg, err := config.Load(layout)
+	if err != nil {
+		return system.Report{}, err
+	}
+	d := &Daemon{
+		layout: layout,
+		config: cfg,
+		runner: system.NewRunner(),
+	}
+	return d.doctorReport(ctx), nil
+}
+
+func (d *Daemon) doctorReport(ctx context.Context) system.Report {
+	report := system.Report{}
+
+	report.AddPreflight("runtime bundle", d.runtimeBundleChecks(), runtimeBundleStatus(d.config))
+	report.AddPreflight("core vm lifecycle", d.coreVMLifecycleChecks(), "required host tools available")
+	d.addCapabilityDoctorChecks(ctx, &report)
+	report.AddPreflight("image build", d.imageBuildChecks(ctx), "image build prerequisites available")
+
+	return report
+}
+
+func (d *Daemon) runtimeBundleChecks() *system.Preflight {
+	checks := system.NewPreflight()
+	hint := paths.RuntimeBundleHint()
+	checks.RequireExecutable(d.config.FirecrackerBin, "firecracker binary", hint)
+	checks.RequireFile(d.config.SSHKeyPath, "ssh private key", `set "ssh_key_path" or refresh the runtime bundle`)
+	checks.RequireFile(d.config.DefaultRootfs, "default rootfs image", `set "default_rootfs" or refresh the runtime bundle`)
+	checks.RequireFile(d.config.DefaultKernel, "kernel image", `set "default_kernel" or refresh the runtime bundle`)
+	if strings.TrimSpace(d.config.DefaultInitrd) != "" {
+		checks.RequireFile(d.config.DefaultInitrd, "initrd image", `set "default_initrd" or refresh the runtime bundle`)
+	}
+	if strings.TrimSpace(d.config.DefaultPackagesFile) != "" {
+		checks.RequireFile(d.config.DefaultPackagesFile, "package manifest", `set "default_packages_file" or refresh the runtime bundle`)
+	}
+	return checks
+}
+
+func (d *Daemon) coreVMLifecycleChecks() *system.Preflight {
+	checks := system.NewPreflight()
+	d.addBaseStartCommandPrereqs(checks)
+	return checks
+}
+
+func (d *Daemon) imageBuildChecks(ctx context.Context) *system.Preflight {
+	checks := system.NewPreflight()
+	d.addImageBuildPrereqs(
+		ctx,
+		checks,
+		firstNonEmpty(d.config.DefaultBaseRootfs, d.config.DefaultRootfs),
+		d.config.DefaultKernel,
+		d.config.DefaultInitrd,
+		d.config.DefaultModulesDir,
+		"",
+	)
+	return checks
+}
+
+func runtimeBundleStatus(cfg model.DaemonConfig) string {
+	if strings.TrimSpace(cfg.RuntimeDir) == "" {
+		return "runtime dir not configured"
+	}
+	return fmt.Sprintf("runtime dir %s", cfg.RuntimeDir)
+}
+
+func firstNonEmpty(values ...string) string {
+	for _, value := range values {
+		if strings.TrimSpace(value) != "" {
+			return value
+		}
+	}
+	return ""
+}

internal/daemon/imagebuild.go

@@ -185,11 +185,16 @@ func (d *Daemon) startImageBuildVM(ctx context.Context, spec imageBuildSpec) (im
 		KernelImagePath: spec.KernelPath,
 		InitrdPath:      spec.InitrdPath,
 		KernelArgs:      system.BuildBootArgs(vm.Name, vm.GuestIP, d.config.BridgeIP, d.config.DefaultDNS),
-		RootDrivePath:   spec.RootfsPath,
-		TapDevice:       vm.TapDevice,
-		VCPUCount:       model.DefaultVCPUCount,
-		MemoryMiB:       model.DefaultMemoryMiB,
-		Logger:          d.logger,
+		Drives: []firecracker.DriveConfig{{
+			ID:       "rootfs",
+			Path:     spec.RootfsPath,
+			ReadOnly: false,
+			IsRoot:   true,
+		}},
+		TapDevice: vm.TapDevice,
+		VCPUCount: model.DefaultVCPUCount,
+		MemoryMiB: model.DefaultMemoryMiB,
+		Logger:    d.logger,
 	})
 	if err != nil {
 		_ = hostnat.Ensure(ctx, d.runner, vm.GuestIP, vm.TapDevice, false)

internal/daemon/preflight.go

@@ -11,56 +11,14 @@ import (
 
 func (d *Daemon) validateStartPrereqs(ctx context.Context, vm model.VMRecord, image model.Image) error {
 	checks := system.NewPreflight()
-	hint := paths.RuntimeBundleHint()
-
-	for _, command := range []string{"sudo", "ip", "dmsetup", "losetup", "blockdev", "truncate", "pgrep", "chown", "chmod", "kill", "e2cp", "e2rm", "debugfs"} {
-		checks.RequireCommand(command, toolHint(command))
-	}
-	checks.RequireExecutable(d.config.FirecrackerBin, "firecracker binary", hint)
-	checks.RequireFile(image.RootfsPath, "rootfs image", "select a valid image or rebuild the runtime bundle")
-	checks.RequireFile(image.KernelPath, "kernel image", `set "default_kernel" or refresh the runtime bundle`)
-	if strings.TrimSpace(image.InitrdPath) != "" {
-		checks.RequireFile(image.InitrdPath, "initrd image", `set "default_initrd" or refresh the runtime bundle`)
-	}
-	if !exists(vm.Runtime.WorkDiskPath) {
-		for _, command := range []string{"mkfs.ext4", "mount", "umount", "cp"} {
-			checks.RequireCommand(command, toolHint(command))
-		}
-	}
-	if vm.Spec.NATEnabled {
-		d.addNATPrereqs(ctx, checks)
-	}
+	d.addBaseStartPrereqs(checks, image)
+	d.addCapabilityStartPrereqs(ctx, checks, vm, image)
 	return checks.Err("vm start preflight failed")
 }
 
 func (d *Daemon) validateImageBuildPrereqs(ctx context.Context, baseRootfs, kernelPath, initrdPath, modulesDir, sizeSpec string) error {
 	checks := system.NewPreflight()
-	hint := paths.RuntimeBundleHint()
-
-	for _, command := range []string{"sudo", "ip", "pgrep", "chown", "chmod", "kill"} {
-		checks.RequireCommand(command, toolHint(command))
-	}
-	checks.RequireExecutable(d.config.FirecrackerBin, "firecracker binary", hint)
-	checks.RequireFile(d.config.SSHKeyPath, "ssh private key", `set "ssh_key_path" or refresh the runtime bundle`)
-	checks.RequireFile(baseRootfs, "base rootfs image", `pass --base-rootfs or set "default_base_rootfs"`)
-	checks.RequireFile(kernelPath, "kernel image", `pass --kernel or set "default_kernel"`)
-	checks.RequireFile(d.config.DefaultPackagesFile, "package manifest", `set "default_packages_file" or refresh the runtime bundle`)
-	if strings.TrimSpace(initrdPath) != "" {
-		checks.RequireFile(initrdPath, "initrd image", `pass --initrd or set "default_initrd"`)
-	}
-	if strings.TrimSpace(modulesDir) != "" {
-		checks.RequireDir(modulesDir, "modules directory", `pass --modules or set "default_modules_dir"`)
-	}
-	if strings.TrimSpace(d.config.DefaultPackagesFile) != "" {
-		if _, err := system.ReadNormalizedLines(d.config.DefaultPackagesFile); err != nil {
-			checks.Addf("package manifest at %s is invalid: %v", d.config.DefaultPackagesFile, err)
-		}
-	}
-	if strings.TrimSpace(sizeSpec) != "" {
-		checks.RequireCommand("e2fsck", toolHint("e2fsck"))
-		checks.RequireCommand("resize2fs", toolHint("resize2fs"))
-	}
-	d.addNATPrereqs(ctx, checks)
+	d.addImageBuildPrereqs(ctx, checks, baseRootfs, kernelPath, initrdPath, modulesDir, sizeSpec)
 	return checks.Err("image build preflight failed")
 }
 
@@ -89,6 +47,53 @@ func (d *Daemon) addNATPrereqs(ctx context.Context, checks *system.Preflight) {
 	}
 }
 
+func (d *Daemon) addBaseStartPrereqs(checks *system.Preflight, image model.Image) {
+	hint := paths.RuntimeBundleHint()
+
+	d.addBaseStartCommandPrereqs(checks)
+	checks.RequireExecutable(d.config.FirecrackerBin, "firecracker binary", hint)
+	checks.RequireFile(image.RootfsPath, "rootfs image", "select a valid image or rebuild the runtime bundle")
+	checks.RequireFile(image.KernelPath, "kernel image", `set "default_kernel" or refresh the runtime bundle`)
+	if strings.TrimSpace(image.InitrdPath) != "" {
+		checks.RequireFile(image.InitrdPath, "initrd image", `set "default_initrd" or refresh the runtime bundle`)
+	}
+}
+
+func (d *Daemon) addBaseStartCommandPrereqs(checks *system.Preflight) {
+	for _, command := range []string{"sudo", "ip", "dmsetup", "losetup", "blockdev", "truncate", "pgrep", "chown", "chmod", "kill", "e2cp", "e2rm", "debugfs"} {
+		checks.RequireCommand(command, toolHint(command))
+	}
+}
+
+func (d *Daemon) addImageBuildPrereqs(ctx context.Context, checks *system.Preflight, baseRootfs, kernelPath, initrdPath, modulesDir, sizeSpec string) {
+	hint := paths.RuntimeBundleHint()
+
+	for _, command := range []string{"sudo", "ip", "pgrep", "chown", "chmod", "kill"} {
+		checks.RequireCommand(command, toolHint(command))
+	}
+	checks.RequireExecutable(d.config.FirecrackerBin, "firecracker binary", hint)
+	checks.RequireFile(d.config.SSHKeyPath, "ssh private key", `set "ssh_key_path" or refresh the runtime bundle`)
+	checks.RequireFile(baseRootfs, "base rootfs image", `pass --base-rootfs or set "default_base_rootfs"`)
+	checks.RequireFile(kernelPath, "kernel image", `pass --kernel or set "default_kernel"`)
+	checks.RequireFile(d.config.DefaultPackagesFile, "package manifest", `set "default_packages_file" or refresh the runtime bundle`)
+	if strings.TrimSpace(initrdPath) != "" {
+		checks.RequireFile(initrdPath, "initrd image", `pass --initrd or set "default_initrd"`)
+	}
+	if strings.TrimSpace(modulesDir) != "" {
+		checks.RequireDir(modulesDir, "modules directory", `pass --modules or set "default_modules_dir"`)
+	}
+	if strings.TrimSpace(d.config.DefaultPackagesFile) != "" {
+		if _, err := system.ReadNormalizedLines(d.config.DefaultPackagesFile); err != nil {
+			checks.Addf("package manifest at %s is invalid: %v", d.config.DefaultPackagesFile, err)
+		}
+	}
+	if strings.TrimSpace(sizeSpec) != "" {
+		checks.RequireCommand("e2fsck", toolHint("e2fsck"))
+		checks.RequireCommand("resize2fs", toolHint("resize2fs"))
+	}
+	d.addNATPrereqs(ctx, checks)
+}
+
 func toolHint(command string) string {
 	switch command {
 	case "ip":

internal/daemon/vm.go

@@ -12,6 +12,7 @@ import (
 
 	"banger/internal/api"
 	"banger/internal/firecracker"
+	"banger/internal/guestconfig"
 	"banger/internal/model"
 	"banger/internal/paths"
 	"banger/internal/system"
@@ -223,8 +224,8 @@ func (d *Daemon) startVMLocked(ctx context.Context, vm model.VMRecord, image mod
 	if err := d.patchRootOverlay(ctx, vm, image); err != nil {
 		return cleanupOnErr(err)
 	}
-	op.stage("work_disk", "work_disk_path", vm.Runtime.WorkDiskPath)
-	if err := d.ensureWorkDisk(ctx, &vm); err != nil {
+	op.stage("prepare_host_features")
+	if err := d.prepareCapabilityHosts(ctx, &vm, image); err != nil {
 		return cleanupOnErr(err)
 	}
 	op.stage("tap", "tap_device", tap)
@@ -243,7 +244,7 @@ func (d *Daemon) startVMLocked(ctx context.Context, vm model.VMRecord, image mod
 	}
 	op.stage("firecracker_launch", "log_path", vm.Runtime.LogPath, "metrics_path", vm.Runtime.MetricsPath)
 	firecrackerCtx := context.Background()
-	machine, err := firecracker.NewMachine(firecrackerCtx, firecracker.MachineConfig{
+	machineConfig := firecracker.MachineConfig{
 		BinaryPath:      fcPath,
 		VMID:            vm.ID,
 		SocketPath:      apiSock,
@@ -252,13 +253,19 @@ func (d *Daemon) startVMLocked(ctx context.Context, vm model.VMRecord, image mod
 		KernelImagePath: image.KernelPath,
 		InitrdPath:      image.InitrdPath,
 		KernelArgs:      system.BuildBootArgs(vm.Name, vm.Runtime.GuestIP, d.config.BridgeIP, d.config.DefaultDNS),
-		RootDrivePath:   vm.Runtime.DMDev,
-		WorkDrivePath:   vm.Runtime.WorkDiskPath,
-		TapDevice:       tap,
-		VCPUCount:       vm.Spec.VCPUCount,
-		MemoryMiB:       vm.Spec.MemoryMiB,
-		Logger:          d.logger,
-	})
+		Drives: []firecracker.DriveConfig{{
+			ID:       "rootfs",
+			Path:     vm.Runtime.DMDev,
+			ReadOnly: false,
+			IsRoot:   true,
+		}},
+		TapDevice: tap,
+		VCPUCount: vm.Spec.VCPUCount,
+		MemoryMiB: vm.Spec.MemoryMiB,
+		Logger:    d.logger,
+	}
+	d.contributeMachineConfig(&machineConfig, vm, image)
+	machine, err := firecracker.NewMachine(firecrackerCtx, machineConfig)
 	if err != nil {
 		return cleanupOnErr(err)
 	}
@@ -272,16 +279,10 @@ func (d *Daemon) startVMLocked(ctx context.Context, vm model.VMRecord, image mod
 	if err := d.ensureSocketAccess(ctx, apiSock); err != nil {
 		return cleanupOnErr(err)
 	}
-	op.stage("dns", "dns_name", vm.Runtime.DNSName)
-	if err := d.setDNS(ctx, vm.Name, vm.Runtime.GuestIP); err != nil {
+	op.stage("post_start_features")
+	if err := d.postStartCapabilities(ctx, vm, image); err != nil {
 		return cleanupOnErr(err)
 	}
-	if vm.Spec.NATEnabled {
-		op.stage("nat")
-		if err := d.ensureNAT(ctx, vm, true); err != nil {
-			return cleanupOnErr(err)
-		}
-	}
 	system.TouchNow(&vm)
 	op.stage("persist")
 	if err := d.store.UpsertVM(ctx, vm); err != nil {
@@ -455,12 +456,6 @@ func (d *Daemon) deleteVMLocked(ctx context.Context, current model.VMRecord) (vm
 	if err := d.cleanupRuntime(ctx, vm, false); err != nil {
 		return model.VMRecord{}, err
 	}
-	if vm.Spec.NATEnabled {
-		op.debugStage("disable_nat")
-		_ = d.ensureNAT(ctx, vm, false)
-	}
-	op.debugStage("remove_dns", "dns_name", vm.Runtime.DNSName)
-	_ = d.removeDNS(ctx, vm.Runtime.DNSName)
 	op.stage("delete_store_record")
 	if err := d.store.DeleteVM(ctx, vm.ID); err != nil {
 		return model.VMRecord{}, err
@@ -538,10 +533,10 @@ func (d *Daemon) setVMLocked(ctx context.Context, current model.VMRecord, params
 	if params.NATEnabled != nil {
 		op.stage("update_nat", "nat_enabled", *params.NATEnabled)
 		vm.Spec.NATEnabled = *params.NATEnabled
-		if running {
-			if err := d.ensureNAT(ctx, vm, *params.NATEnabled); err != nil {
-				return model.VMRecord{}, err
-			}
+	}
+	if running {
+		if err := d.applyCapabilityConfigChanges(ctx, current, vm); err != nil {
+			return model.VMRecord{}, err
 		}
 	}
 	system.TouchNow(&vm)
@@ -684,14 +679,34 @@ func (d *Daemon) patchRootOverlay(ctx context.Context, vm model.VMRecord, image
 	if err != nil {
 		fstab = ""
 	}
-	newFSTab := system.UpdateFSTab(fstab)
-	for guestPath, data := range map[string][]byte{
-		"/etc/resolv.conf":                      resolv,
-		"/etc/hostname":                         hostname,
-		"/etc/hosts":                            hosts,
-		"/etc/fstab":                            []byte(newFSTab),
-		"/etc/ssh/sshd_config.d/99-banger.conf": sshdConfig,
-	} {
+	builder := guestconfig.NewBuilder()
+	builder.WriteFile("/etc/resolv.conf", resolv)
+	builder.WriteFile("/etc/hostname", hostname)
+	builder.WriteFile("/etc/hosts", hosts)
+	builder.WriteFile("/etc/ssh/sshd_config.d/99-banger.conf", sshdConfig)
+	builder.DropMountTarget("/home")
+	builder.DropMountTarget("/var")
+	builder.AddMount(guestconfig.MountSpec{
+		Source:  "tmpfs",
+		Target:  "/run",
+		FSType:  "tmpfs",
+		Options: []string{"defaults", "nodev", "nosuid", "mode=0755"},
+		Dump:    0,
+		Pass:    0,
+	})
+	builder.AddMount(guestconfig.MountSpec{
+		Source:  "tmpfs",
+		Target:  "/tmp",
+		FSType:  "tmpfs",
+		Options: []string{"defaults", "nodev", "nosuid", "mode=1777"},
+		Dump:    0,
+		Pass:    0,
+	})
+	d.contributeGuestConfig(builder, vm, image)
+	builder.WriteFile("/etc/fstab", []byte(builder.RenderFSTab(fstab)))
+	files := builder.Files()
+	for _, guestPath := range builder.FilePaths() {
+		data := files[guestPath]
 		if err := system.WriteExt4File(ctx, d.runner, vm.Runtime.DMDev, guestPath, data); err != nil {
 			return err
 		}
@@ -878,14 +893,11 @@ func (d *Daemon) cleanupRuntime(ctx context.Context, vm model.VMRecord, preserve
 		DMName:   vm.Runtime.DMName,
 		DMDev:    vm.Runtime.DMDev,
 	})
-	if vm.Spec.NATEnabled {
-		_ = d.ensureNAT(ctx, vm, false)
-	}
-	_ = d.removeDNS(ctx, vm.Runtime.DNSName)
+	featureErr := d.cleanupCapabilityState(ctx, vm)
 	if !preserveDisks && vm.Runtime.VMDir != "" {
-		return errors.Join(snapshotErr, os.RemoveAll(vm.Runtime.VMDir))
+		return errors.Join(snapshotErr, featureErr, os.RemoveAll(vm.Runtime.VMDir))
 	}
-	return snapshotErr
+	return errors.Join(snapshotErr, featureErr)
 }
 
 func clearRuntimeHandles(vm *model.VMRecord) {