Boot a Firecracker microVM from a kernel and root filesystem via the Firecracker API (boot-source, drives, network, InstanceStart)

Documented steps

1. Start Firecracker against a unix socket: firecracker --api-sock /tmp/firecracker.socket --enable-pci (--enable-pci uses PCI VirtIO transport instead of legacy MMIO for higher throughput/lower latency)
2. Configure the boot source: curl -X PUT --unix-socket /tmp/firecracker.socket -d '{"kernel_image_path":"./vmlinux","boot_args":"console=ttyS0 reboot=k panic=1"}' http://localhost/boot-source
3. Attach the root filesystem as a block device: curl -X PUT --unix-socket /tmp/firecracker.socket -d '{"drive_id":"rootfs","path_on_host":"./rootfs.ext4","is_root_device":true,"is_read_only":false}' http://localhost/drives/rootfs
4. Add a network interface backed by a host TAP: create the TAP (ip tuntap add dev tap0 mode tap; ip addr add 172.16.0.1/30 dev tap0; ip link set tap0 up), enable ip_forward + iptables MASQUERADE for outbound NAT
5. Attach the interface: curl -X PUT --unix-socket /tmp/firecracker.socket -d '{"iface_id":"net1","guest_mac":"06:00:AC:10:00:02","host_dev_name":"tap0"}' http://localhost/network-interfaces/net1
6. API requests are handled asynchronously, so wait for config to settle, then start: sleep 0.015; curl -X PUT --unix-socket /tmp/firecracker.socket -d '{"action_type":"InstanceStart"}' http://localhost/actions
7. Inside the guest set the default route via the host TAP IP and add DNS: ip route add default via 172.16.0.1 dev eth0; echo 'nameserver 8.8.8.8' > /etc/resolv.conf