# LoRA training worker

A small host service on **irv-ml1** that runs **sd-scripts** SDXL LoRA training on demand
for **arbo**. It is the infra-ops half of the "in-arbo LoRA training, Phase 1" split:

- **infra-ops (this service)** owns the training worker — the ONLY thing that invokes
  `accelerate launch`. Runs as `llmuser` (the only user that can exec `/opt/fluxgym/.venv`
  and owns the GPU-training surface).
- **comfy-dev (arbo)** owns dispatch, the GPU scheduler + serving-pause, the training-job
  model + durable history + status proxy, and the Studio UI.

Canonical contract: `vh/arbo` → `docs/contracts/in-arbo-lora-training-phase1.contract.md`
(§4.1 worker API, §2 ownership, §4.6 recipe, §7 open items). This service implements §4.1.

## Design posture

- **Fixed invocation only (INV-T7).** arbo sends *bounded parameters*; the worker builds
  exactly one command shape (`sdxl_train_network.py` with the §4.6 lean flag set). There is
  no path from a request to a free-form argument — see `worker/invocation.py`. Every param
  is range/allowlist/path-containment checked before a process is spawned; a bad request is
  a 422, never a silent downgrade.
- **Thin supervisor.** The worker never imports torch/sd-scripts. It *subprocesses* the
  fluxgym venv's `accelerate`, so this process stays tiny and the fluxgym venv stays pristine.
- **One job at a time (§4.1).** arbo's lease is the real serializer (INV-T2); the worker's
  409 is a backstop.
- **Durable (§4.3 boot reconciliation).** Job records persist to JSON; on restart a
  non-terminal job whose OS process is gone is marked `failed` so arbo never sees a phantom
  `training` after a worker blip.

## Wire-shape (the §7 open items, resolved with comfy-dev)

1. **Mount / handoff.** Shared host dir `/worktank/arbo/train/{train_id}/`, group `arbotrain`
   (setgid 2770), members `lkraven` (arbo container uid = 1000) + `llmuser` (worker, uid 1001)
   → both rw, new files inherit the group. arbo adds one bind to its compose:
   `- /worktank/arbo/train:/worktank/arbo/train`. arbo (container) writes `dataset_dir` + the
   kohya folder; the worker (llmuser) reads it and writes `output_dir`; arbo reads the
   `.safetensors` for download. **Never** via `/data` (arbo-only volume).
2. **Bind.** Worker binds `0.0.0.0:8203`. arbo (containerized, traefik-net bridge — host
   loopback unreachable) reaches it via `host.docker.internal:8203` with
   `extra_hosts: ["host.docker.internal:host-gateway"]` in arbo's compose.
3. **TTS-liveness signal.** `GET /gpu-status` reports per-device VRAM (index 0 = 3090,
   index 1 = A6000 under `CUDA_DEVICE_ORDER=PCI_BUS_ID`) + `tts_on_3090`. arbo polls it before
   assigning `device_index` and steers a lean train to the A6000 when TTS is live on the 3090.

## API (§4.1)

| Method + path | Purpose |
|---|---|
| `POST /train` | dispatch a train (409 if busy, 422 on invalid params) → `{worker_job_id}` |
| `GET /train/{id}` | `{status, step, total_steps, loss, eta_s, lora_path?, error?}` |
| `GET /train/{id}/log` | tail of the run log |
| `POST /train/{id}/cancel` | best-effort kill → `cancelled` |
| `GET /gpu-status` | per-device VRAM + `tts_on_3090` |
| `GET /healthz` | liveness + active job id |

`POST /train` body: `{dataset_dir, base_model_path, output_dir, output_name, trigger,
subject_class, repeats, tier, device_index, seed}`. `tier ∈ {fast, balanced, quality}` →
(steps, dim, res) = (400,16,768) / (1500,32,768) / (3000,32,1024). `quality` (1024) requires
`device_index=1` (A6000) — `quality` on the 3090 is a 422.

## Recipe hyperparameters

The contract §4.6 pins the flag *set* + tier→(steps,dim,res) but not lr/scheduler/batch.
Those live as auditable constants in `worker/config.py::SDXL_HPARAMS` (lr 1e-4, cosine,
adamw8bit, min_snr_gamma 5, noise_offset 0.1, batch 1/2 lean/full). **These are
agent-discretion defaults pending a cross-check against the proven Sindra runs** — adjust in
one place if Sindra used different values.

## Deploy

Privileged host setup (group, dirs, /opt install, venv, systemd) is delegated to `infra-ops`
via the elway playbook (needs NOPASSWD sudo on irv-ml1, which infra-ops has):

```bash
# from the eshpfi-management repo root
scripts/elway irv-ml1 --playbook playbooks/deploy-lora-training-worker.yaml
```

The playbook is idempotent: creates the `arbotrain` group + `/worktank/arbo/train` (2770
setgid), rsyncs the code to `/opt/lora-training-worker`, builds the worker venv with `uv`,
installs + enables the systemd unit, and health-gates on `GET /healthz`.

## Test

```bash
cd services/lora-training-worker
uv run --with pytest python -m pytest -q     # invocation-builder (INV-T7) unit tests
```

## Status

- ✅ Worker code + INV-T7 invocation builder + tests (14 green).
- ⬜ Box deploy (elway playbook) + live `/healthz` + `/gpu-status` smoke.
- ⬜ First real end-to-end train once arbo dispatches a studio dataset (arbo backend built +
  dormant; waits on this worker).
- ⬜ Sindra hyperparameter cross-check.