140 lines
7.4 KiB
Markdown
140 lines
7.4 KiB
Markdown
# CLAUDE.md — Diskless Fleet Boot System
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This repo builds the boot system for a fleet of diskless hosts:
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PXE/HTTP-booted, authenticating to the network with **802.1X EAP-TLS using a
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TPM-held key**, running **MACsec** on the access link, and mounting an
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immutable **erofs + dm-verity root over NVMe/TCP**. Each release is a signed
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**UKI** plus root image packaged as a **FROM-scratch OCI artifact image**.
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The authoritative architecture document is
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`docs/diskless-fleet-design-v2.pdf` — read it before structural changes.
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## Repo layout
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```
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diskless.pkr.hcl Packer template (qemu builder)
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http/ks.cfg Kickstart for the throwaway build VM
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files/dracut/95dot1x-macsec/ Custom dracut module (the heart of the system)
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files/etc/dot1x/ Supplicant config + RADIUS CA (placeholder)
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files/etc/dracut.conf.d/90-diskless.conf no-hostonly + drivers + modules
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files/etc/NetworkManager/ NM unmanaged-device config
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scripts/extract-artifacts.sh qcow2 -> kernel/initramfs/erofs+verity/cmdline
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scripts/build-oci.sh ukify + sbsign + roothash gate + OCI image
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docs/ Design PDF and supporting notes
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```
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## Build & test commands
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```bash
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packer init .
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packer validate . # always before committing template changes
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packer build -var image_version=X.Y.Z \
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-var nic_drivers="ice mlx5_core" \
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-var oci_image=<registry>/fleet-boot . # add sb_key/sb_cert for signed builds
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bash -n files/dracut/95dot1x-macsec/*.sh scripts/*.sh # shell syntax gate
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shellcheck files/dracut/95dot1x-macsec/*.sh scripts/*.sh
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```
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Build-host deps: qemu-kvm, libguestfs-tools, erofs-utils, cryptsetup, jq,
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systemd-ukify, sbsigntools, buildah (or docker).
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## Architecture invariants — do not violate these
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These encode failure modes that brick the fleet. Treat them as hard
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constraints; if a task appears to require breaking one, stop and flag it
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instead of working around it.
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1. **No per-host state in any artifact, ever.** No hostnames, keys, certs,
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MACs, or per-host config in the initramfs, rootfs, UKI, or OCI image.
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All host identity derives from the TPM at runtime (key at persistent
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handle `0x81010001`, cert at NV index `0x01800001`, hostnqn derived from
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the cert serial). If a change needs per-host data, it belongs in the
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enrolment flow, not the image.
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1. **The hook ordering in `dot1x-macsec-up.sh` is load-bearing.**
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NV-cert extraction → supplicant start → wait for `Authorized` + macsec0 →
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DHCP **on macsec0** → hostnqn derivation. Never DHCP before auth
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completes (pre-auth leases are invalid after VLAN assignment); never
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connect NVMe before macsec0 is addressed.
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1. **The supplicant must survive switch-root.** It is launched with
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`exec -a @wpa_supplicant` (systemd root-storage-daemon convention) and
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its state lives under `/run`. Do not “clean up” the `@`, move state off
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`/run`, or hand the interface to NetworkManager — MKA times out in ~6 s
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without keepalives and the root filesystem link dies. The NM
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unmanaged-devices config exists for this reason; keep it in sync with
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interface naming.
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1. **roothash coupling is a hard gate.** `build-oci.sh` refuses to build if
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the `roothash=` in the UKI cmdline ≠ `verity.json`. Never weaken, skip,
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or warn-instead-of-fail this check: a mismatched UKI/rootfs pair is an
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unbootable fleet.
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1. **The UKI cmdline is immutable once signed.** Any cmdline change
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(including `NVMET_TRADDR`) requires a rebuild + re-sign. Prefer a
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per-environment DNS name for NVMe discovery over per-environment builds.
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1. **Signing keys never enter the build VM or this repo.** `sb_key` /
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`sb_cert` are CI/HSM-provided paths on the build host. Never commit key
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material, never copy keys into provisioner steps, never echo them in
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logs. Unsigned builds are lab-only and must keep their loud warning.
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1. **Reproducibility of the root image is a security property.**
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`mkfs.erofs` runs with fixed UUID and `-T 0`; the verity root hash must
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be a pure function of the input tree. Don’t introduce timestamps,
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random seeds, or build-host paths into the rootfs.
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1. **The initramfs is built `--no-hostonly` and contents are asserted.**
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The build VM is virtio-only; real NIC drivers, `macsec`, `nvme-tcp`,
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erofs, and veritysetup are explicitly listed in
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`90-diskless.conf` and checked via `lsinitrd | grep` in the template.
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When adding a runtime dependency to the hook, add it to the dracut
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module’s `install()` *and* extend the lsinitrd assertion.
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1. **The OCI artifact image stays FROM scratch.** Only
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`/artifacts/{fleet-<ver>.efi, rootfs.erofs, verity.json, SHA256SUMS}`.
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No shell, no tools, no base image. Serving software (SPDK, nginx) lives
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in separate, independently versioned images — never merge them into the
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artifact image.
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1. **Deployments are pinned by digest.** One commit per fleet release in
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the deployment manifest; that manifest is the single source coupling
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UKI ↔ namespace. Rollback = revert the commit.
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## Things that look like bugs but aren’t
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- `identity="fleet-host"` in the supplicant config is intentionally generic;
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RADIUS derives real identity from the certificate CN/SAN.
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- `/etc/machine-id` is truncated empty in the image; each host generates its
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own into the tmpfs overlay at boot.
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- `/etc/fstab` is effectively empty; root comes from netroot + verity.
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- The build VM has no TPM. Correct — nothing host-specific exists at build
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time. CI boot tests use swtpm.
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- `files/etc/dot1x/radius-ca.pem` is a placeholder; builds succeed with it
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but authentication cannot. Replace per environment, don’t commit real
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internal CA material unless the repo’s classification allows it.
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## Known bench-verify items (check before trusting a change in production)
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- TPM key reference method in wpa_supplicant: `private_key="handle:..."`
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via OpenSSL tpm2 provider vs tpm2-pkcs11 URI — depends on the distro
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build; the supplicant config carries both options.
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- erofs module availability on the target RHEL kernel (fallback:
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journal-less ext4 in `extract-artifacts.sh`).
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- `systemd.verity_root_options=hash-offset` support in the shipped systemd
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(fallback: split data/hash into two namespaces).
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- `network-legacy` dracut module availability (the hook’s `ifup` step needs
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porting if a future release drops it).
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## Testing changes
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Full boot-chain smoke test runs in QEMU/Proxmox: swtpm (test key at the
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fleet handle, test cert in NV) + hostapd as wired 802.1X/MACsec
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authenticator + FreeRADIUS on a veth/bridge (bridge needs
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`group_fwd_mask=8` or EAPOL is silently dropped). Pass criteria: port
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`Authorized`, macsec0 addressed, NVMe namespace connected, verity root
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mapped, overlay writable, supplicant alive after switch-root.
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Any change to the dracut module, supplicant config, or cmdline must pass
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this before merge. Template-only changes need `packer validate` +
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shellcheck at minimum.
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## Conventions
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- Shell: bash, `set -euo pipefail` in scripts (dracut hooks source
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dracut-lib instead and must stay POSIX-ish bash compatible with the
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initramfs environment — no GNU-only tools not installed by the module).
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- Keep comments that explain *why* (timing constraints, kernel behaviours);
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they encode bench findings that are expensive to rediscover.
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- Versioning: semver on `image_version`; the OCI tag matches; the git tag
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matches; one release == one digest == one manifest commit. |