# Design v2 — implementation errata (RHEL/Rocky 9) Records where the as-built implementation diverges from `diskless-fleet-design-v2.pdf`. The PDF remains authoritative for the architecture; this note captures deltas discovered bringing the build up on **Rocky 9.8** until they are folded into a consolidated **v3**. Last updated 2026-06-22. The architecture is unchanged: 802.1X EAP-TLS with a TPM-held key, MACsec on the access link, dm-verity-protected erofs root over NVMe/TCP, signed UKI, and the FROM-scratch OCI release artifact. Only the items below differ. ## 1. Design-level change — writable root overlay **PDF says (§3 step 8, §5):** runtime state lives on a tmpfs overlay enabled by the kernel cmdline option **`rootovl`**. **As built:** the cmdline uses **`systemd.volatile=overlay`** instead. **Why:** `rootovl`/`overlayfs` is a Debian/third-party dracut module; RHEL/Rocky dracut does not ship it (`dracut: module 'overlayfs' cannot be found`). `systemd.volatile=overlay` is the RHEL-native, systemd-supported mechanism and is the recommended overlay for dm-verity-protected read-only roots. Behaviour is equivalent: the verity erofs root mounts read-only and a tmpfs overlay carries runtime writes; per-host `machine-id` is still generated into the overlay. **Caveat:** requires `systemd-volatile-root.service` in the initramfs (bundled by recent dracut; `install_items` it if the root stays read-only at boot). The known failure mode is NFS root — not applicable here (NVMe block root). Set in [../scripts/extract-artifacts.sh](../scripts/extract-artifacts.sh); module list in [../files/etc/dracut.conf.d/90-diskless.conf](../files/etc/dracut.conf.d/90-diskless.conf). ## 1b. Design-level change — dm-verity uses two namespaces, not in-file offset **PDF says (§5):** the erofs data and the dm-verity hash tree share a single NVMe/TCP namespace, appended in one file and split on the host with `systemd.verity_root_options=hash-offset=`. **As built:** data and hash are **two separate namespaces** — `rootfs.erofs` (data) and `rootfs.hash` (hash tree) — each a file in the OCI artifact, served as its own NVMe namespace with a distinct pinned UUID. The cmdline uses `systemd.verity_root_data=` / `systemd.verity_root_hash=` by-id devices with no offset. **Why:** Rocky 9.8 `systemd-veritysetup` does not support `hash-offset=` — it logs `Encountered unknown option 'hash-offset=…', ignoring` then `Failed to load verity superblock: invalid argument`, so the single-namespace layout never maps `/dev/mapper/root`. Two namespaces is the design's own documented fallback and uses systemd's native verity (no custom activation code; keeps root-hash signature support for production). Devices are referenced by stable `/dev/disk/by-id/nvme-uuid.` (not `/dev/nvmeNnM`) because controller indices shift with the transient discovery controller. **Touches:** [../scripts/extract-artifacts.sh](../scripts/extract-artifacts.sh) (emits `rootfs.hash`, two UUIDs, offset-free cmdline), [../scripts/build-oci.sh](../scripts/build-oci.sh) (artifact list + SHA256SUMS), [../serving/spdk-setup.sh](../serving/spdk-setup.sh) (2nd bdev/namespace), and CLAUDE.md invariant #9. ## 1c. Design-level addition — pre-auth boot path & per-host identity enrolment Two design points the PDF leaves implicit; both are load-bearing for the secure model and are recorded here pending v3. **The boot path is inherently pre-auth, so a pre-auth permit-set is mandatory.** The firmware (UEFI HTTP boot / PXE→iPXE) fetches the UKI **before** any OS or supplicant exists — there is no firmware 802.1X supplicant — so the UKI/initramfs fetch always happens in the unauthenticated state. The secure model therefore requires the authenticator to permit a *scoped* set of services pre-auth (DHCP/DNS + TFTP + HTTP to the serving host) and only complete 802.1X once the **OS** is running; RADIUS returns the secure VLAN on Access-Accept, after which DHCP-for-the-running-system and the NVMe/TCP root ride **`macsec0`** (post-auth, encrypted). Mechanism on a real switch: low-impact 802.1X / a pre-auth dACL / boot→secure dynamic VLAN. Consequences: - Pre-auth traffic has **no MACsec** (plaintext at L2). Integrity of the boot therefore comes from **Secure Boot** (the signed UKI + signed `fleet-ipxe`), not the network — this is *why* signing matters: the boot transport is untrusted. - `hostapd` wired (the bench authenticator) is strictly port-based and can't model a pre-auth per-flow permit — the in-place pre-auth ACL is a real-switch feature, validated on the 820's switch, not the VM rig (see `serving/dot1x-bench/`). **Per-host 802.1X identity is created by an enrolment flow, never baked in** (invariant #1). Chosen pattern: **trust-on-first-use with out-of-band fingerprint approval** — on an empty TPM the host generates a key *in* the TPM (`0x81010001`), submits a CSR to an enrolment **broker** (reachable via the same pre-auth permit-set, e.g. an `/enrol/` location on the serving nginx → broker → step-ca signer), and shows a fingerprint on the Plymouth splash; an admin cross-checks it and approves; the signed cert is written to NV `0x01800001` and authentication proceeds. Enrol triggers on **empty-NV only** (expired cert → automatic renew; auth-failure-with-cert → alert, not re-enrol). The fingerprint authorises *which device*; **TPM attestation** (step-ca ACME `device-attest-01`) proves *key residency* — use both for full assurance. Runs in a provisioning UKI/mode, not the production initramfs. Full design + decisions: **TODO #11** (the network-identity counterpart to **#10**, which enrols Secure Boot PK/KEK/db; both share the provisioning-UKI vehicle). ## 2. Implementation notes (not architectural) These don't contradict the PDF (it doesn't specify them) but are worth recording. - **Network backend.** The dracut hook uses the `network-manager` dracut module (ported 2026-06-17 from `network-legacy`/`ifup`/`dhclient`). NM hands its initramfs connections to the real-root NetworkManager, which **renews the DHCP lease** in the running system — network-legacy's one-shot lease was never renewed, so the address dropped at lease expiry and the NVMe/TCP root died. Managed/unmanaged is mode-aware: secure path → `macsec0` managed (NM DHCPs + renews it), physical `en*` unmanaged (wpa_supplicant owns EAPOL/MKA), enforced by the `nm-unmanaged.sh` cmdline hook writing a `/run/NetworkManager/conf.d` drop-in before NM starts; test path → boot NIC managed, hook is a no-op. No static unmanaged file (it couldn't be mode-aware). Awaiting boot-bench verify. - **Build ISO.** Defaults to a version-pinned Rocky 9.x **minimal** ISO on the internal mirror (`iso_url` + `sha256` `iso_checksum`). `http/ks.cfg` installs only core+sshd+chrony from the ISO; the diskless tooling is pulled online by the provisioner, so the build VM needs outbound repo access. - **Reference serving stack.** §7's SPDK + nginx + DHCP/DNS serving stack has a concrete docker-compose implementation in [../serving/](../serving/), incl. Docker image-volume mounting of the OCI artifact image. - **STIG hardening.** DISA STIG (SSG) is applied with a diskless/UKI/kiosk tailoring; several rule families are deviated because the architecture makes them N/A (no partitions, no GRUB, AIDE→dm-verity) or by lab decision (FIPS off, firewall off, audit local-only). Full rationale + compensating controls: [stig-deviations.md](stig-deviations.md). STIG kernel params live in the UKI cmdline (the no-GRUB compensating control). - Assorted build-time fixes (HCL `%%{` escaping, file-provisioner staging, dracut module naming) are documented in [../CLAUDE.md](../CLAUDE.md) → "RHEL 9.x build notes". ## 3. Temporary deviation — must be reverted before production - **802.1X/MACsec test bypass.** `disable_dot1x=true` bakes `rd.dot1x=0` into the cmdline so the host skips authentication/MACsec and DHCPs the NIC directly, to validate the UKI/rootfs/NVMe-oF path on an open switch port. The auth stack stays in the image (dormant). This is **lab-only**; a production build must drop the flag (`DISABLE_DOT1X: "false"` in CI) to restore the secure boot chain described throughout the PDF.