Netboot installer: TFTP/HTTP servers, initramfs, EEPROM artifacts, plan

docs/PLAN.md

@@ -28,6 +28,36 @@
 - Synology NAS on same LAN — shared storage target (NFS) for cluster
   workloads
 
+## Rebuild architecture (decided 2026-09-19)
+
+Fully unattended network reimage, no per-node physical access:
+
+- **Synology** (`192.168.1.157`) hosts three services (all auto-start, see
+  `configs/`):
+  - `planck-tftp.service` — custom python TFTP server on :69 serving
+    `/volume1/plancknetboot/tftp/` (firmware, kernel, installer initramfs)
+  - `planck-netboot.service` — python HTTP helper on :8000 (GET `rootfs.tar`
+    template, GET `/events/<name>` progress log, POST = upload)
+  - NFS read-only export of the share for future use
+- **Installer initramfs** (`configs/installer-init.sh`): busybox + sfdisk +
+  e2fsprogs. Identifies the node by CPU serial (map in
+  `configs/hostmap`), wipes `/dev/sda`, downloads the Debian 13 Raspberry Pi
+  OS Lite template over HTTP, installs it, sets hostname/ssh keys/user,
+  POSTs `pieeprom-revert.upd/.sig` to `tftp/<serial>/`, reboots.
+- **Bootloader flow**: nodes' EEPROM is flashed (via staged `pieeprom.upd`
+  from the old OS) to install-mode: `BOOT_ORDER=0xf142` (network first),
+  `TFTP_IP=192.168.1.157`, `TFTP_PREFIX=1` (per-serial dirs),
+  `ENABLE_SELF_UPDATE=1`. After install, the TFTP-served
+  `bootloader_update=1` config + `<serial>/pieeprom.upd` reverts the node to
+  `BOOT_ORDER=0xf14` (USB first). Fresh OS boots from SSD; firstboot service
+  tidies up.
+- **Reinstall a node anytime**: stage install-mode EEPROM again + reboot
+  (delete `tftp/<serial>/pieeprom.*` on the Synology first if it exists).
+- Node password: see `configs/node-password.txt` (gitignored). SSH is
+  key-based; password exists for console/sudo recovery.
+- UniFi MFA blocks API access; DHCP reservations deferred — mDNS
+  (`planck0NN.local`) works across subnets today.
+
 ## Phases
 
 - [x] Phase 0 — Access + inventory (SSH keys on all 20, docs/)