Understand which devices each Firecracker API endpoint depends on (device-requirement matrix) to avoid 400 BadRequest on boot

Documented steps

1. Reference the Device-API functionality matrix: an endpoint marked R (Required) for a device fails with HTTP 400 if that device is missing, while O (Optional) endpoints succeed without it
2. Key required dependencies: /drives/{id} requires a virtio-block or vhost-user-block device; /network-interfaces/{id} and /mmds plus /mmds/config require a virtio-net device; /mmds/config also requires at least one network interface; /entropy requires the virtio-rng device; /pmem/{id} requires virtio-pmem; /serial requires a serial console; /vsock requires a virtio-vsock device; /hotplug/memory requires virtio-mem
3. boot-source, cpu-config, machine-config, logger, metrics, vm and snapshot endpoints have no required devices (all O) and can be called before any devices are attached
4. Use this before scripting a boot sequence so you attach the matching device for every endpoint you intend to call
5. Device attach ordering is up to you, but each endpoint validates that its required device exists at call time