t1→t2 hypervisor: 3224 ms → 264 ms (12×). 128 MiB guest now boots
cleanly without OOM, reverting the temporary 512 MiB bump.
Root causes:
1. build-microvm-image.sh staged the entire chroot into the cpio
without dropping /boot, embedding a duplicate vmlinuz, Alpine's
stock initramfs-virt, System.map, and a "boot → ." symlink loop
(~25 MiB). Decompression peak exceeded 128 MiB. Strip /boot after
the kernel is copied out, before the cpio. Initramfs drops from
31 MiB → 11 MiB (53 MiB → 28 MiB uncompressed); total artifact
42 MiB → 22 MiB.
2. vm/lifecycle.go burned 3 s of fixed sleep on every direct-boot
launch: 2 s nbdkit pre-exec wait (no nbdkit on direct-boot) and
1 s post-fork settle (QEMU binds QMP within ~10 ms when there is
no firmware, ROM, or block layer). Both extracted to
directBoot-aware helpers — nbdkitPreExecWait collapses to 0, and
qemuStartSettleWait to 50 ms.
3. KernelCmdline only carried `console=ttyS0 virtio_mmio.device=…`.
Added boot-time perf flags: quiet loglevel=3 (silence printk over
115200-baud isa-serial), mitigations=off (KVM guest on trusted
host, single-tenant LB workload), tsc=reliable, no_timer_check,
reboot=t, i8042.{nopnp,noaux,nokbd} (microvm has no PS/2).
4. init.sh dropped modprobe virtio_mmio (built-in:
CONFIG_VIRTIO_MMIO=y) and tightened polling: fw_cfg/iface waits go
from 10 × 200 ms (up to 2 s) to 5 × 20 ms (up to 100 ms).
Phase 2 gates:
- t1→t2 ≤ 300 ms ✅ 264 ms / 281 ms
- artifact ≤ 50 MiB ✅ 22 MiB (gate already in build script)
- ELBv2 e2e green ✅ 32/33 (pre-existing client-VM failure,
unrelated to microvm path)
virtio_net depends on net_failover/failover for live-migration support.
Stripping them left virtio_net with unresolved symbols
(net_failover_create/destroy), so the module failed to load and the
guest came up with only lo. init.sh then skipped every NIC ("no
interface found for MAC ..."), leaving lb-agent with no network path
to AWSGW and the LB stuck in provisioning.
Add *failover*.ko* to the keep-list. Image size unchanged at 42 MiB
(under the 50 MiB Phase 2 gate). ELBv2 e2e now reaches active and
2/2 targets healthy for both ALB and NLB internal LBs.
The directory-only keep-list (drivers/virtio, drivers/firmware) missed
virtio_net.ko which lives in drivers/net/, virtio_blk in drivers/block/,
and virtio-rng in drivers/char/hw_random/. Switch to find-based approach:
collect all virtio*.ko* and *fw_cfg*.ko* regardless of subdirectory, then
restore them into their original relative paths under kernel/.
Artifacts now: 42 MiB (vmlinuz 11 MiB + initramfs 31 MiB), gate passes.
tar extraction without root silently demotes device files to 0-byte regular
files (mknod requires CAP_MKNOD). The kernel opens /dev/console when wiring
init's stdio to the serial console; a regular file there causes all init output
to be silently discarded to RAM — the VM appears stuck at 'Run /init as init
process' with no subsequent console output and lb-agent never heartbeats.
Fix: after rootfs population, wipe /dev and recreate console (c 5 1) and
null (c 1 3) via sudo mknod. devtmpfs provides all other devices at runtime
once init.sh mounts it.
joshsiv-mulga