bvandeusenandClaude Opus 5
445164c852
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Operator, 2026-09-23: *"auto should be always on, not a setting, so that idle
instances quiet down when not running. the number that is visible and
something the user can tweak and manage should be the cap itself the number of
running workers is handled by the autoscaling function which is always on."*
They are right, and the reason it was not built this way is worth stating: the
manual dial came first (steps 2-4) and the autoscaler came last (step 7), as
an opt-in BESIDE a control that already existed. Nothing ever asked whether
the dial should still exist once something could move it automatically. Each
step was defensible; the result was three operator settings over one number.
## `slots`, `enabled` and `autoscale` are gone
`slots` was a MEASUREMENT wearing a preference's clothes. How many workers a
lane runs is read live and moved every minute; storing it meant the operator
had to keep two numbers in agreement and the autoscaler had to be told it was
allowed to touch one of them.
`autoscale` gated the mechanism behind a choice, so a lane nobody opted in
never gave its workers back — which is why an idle instance never quieted
down.
`enabled` is derived: a cap of zero means no consumers. "Off" and "may use no
workers" were two spellings of one fact, stored separately, free to disagree.
## Two sweeps become one
`reconcile_lanes_sync` drove the pool to the stored `slots`; `autoscale_lanes_
sync` moved it away from that same number; and most of step 7's hardest
reasoning — a stored value that is a FLOOR, a target of `max(stored, current)`
— existed only to stop them fighting. Delete the stored number and the problem
is not solved, it is absent.
`size_lanes_sync` runs every minute and owns both consumers and pool size. It
also subsumes what the reconcile was for: a worker restarted at its ENV
concurrency is corrected on the next tick rather than after five.
Growth is immediate, shrink is one worker per tick. Deliberately asymmetric —
"always on" is only pleasant if the ramp keeps up, and +1/minute would take
four minutes to answer a burst. Being one worker too large for a minute costs
a sleeping process; being too small costs work not happening. For ML the
asymmetry matters most: every new slot reloads a multi-GB model, so the slow
shrink is what stops a quiet patch from paying that cost again a minute later.
## The caps ship at one, and zero for ML
Per the operator. Conservative on purpose — and a conservative default nobody
knows how to raise is just a slow product, which is the other half of what
they asked for:
"there needs to be something that tells the user to bump those numbers to
improve processing rate or they'd never know the controls exist."
So a lane running everything its cap allows while work piles up says so, in
its own row, with the headroom named: *"4,060 waiting and all 1 worker busy.
Raise the cap to run more at once — this machine allows up to 7."*
It fires only when raising the cap would actually help. Not when the lane is
keeping up, not when the sizing pass has room it has not taken, and not at the
machine ceiling — where "raise the cap" is advice nobody can take.
## Migration 0105 rewrites the caps rather than carrying them
The old defaults (4/2/2/1) bounded a manual control and were loose because
moving within them was the ordinary act. The number now means "the most
workers this lane may use", which is a different promise; carrying the old
figure over would quadruple the worker lane on every existing install at the
moment this deploys.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LVjrnpQjRgHdvq95rASoiR
94 lines
3.6 KiB
Python
94 lines
3.6 KiB
Python
"""Worker lanes: what each is doing, and the dial that changes it.
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Milestone 422 step 2. The write half of a surface `api/system_activity.py`
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only reads.
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## Why this is a separate blueprint
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`system_activity` says in its own first line that it is read-only, and it
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answers a different question: its `/workers` is keyed on celery HOSTNAME and
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reports which nodes answered. That stays as it is — the existing
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SystemActivityTab consumes it.
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This is keyed on LANE, joins the stored cap to the live pool, and accepts
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writes. Two endpoints answering "which celery processes exist" and "how much
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work is each lane allowed to do" are not the same endpoint, and folding the
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second into the first would make a read-only module a write one.
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"""
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from __future__ import annotations
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from datetime import UTC, datetime
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from quart import Blueprint, jsonify, request
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from ..extensions import get_session
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from ..services.worker_control import LaneUpdateRefused, lane_view, set_lane
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from ..services.worker_lanes import LANES_BY_NAME
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from ._responses import error_response as _bad
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workers_bp = Blueprint("workers", __name__, url_prefix="/api/system/workers")
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@workers_bp.route("", methods=["GET"])
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async def list_lanes():
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"""Every lane: its cap, the ceiling above it, and what is live.
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Response: {lanes: [...], fetched_at: iso8601}
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Deliberately NOT cached, unlike system_activity's 2s/5s caches. This is
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the surface an operator watches while dragging a stepper, and a cached
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reply would show them the value from before their own change and read as
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the control having failed.
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"""
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async with get_session() as session:
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lanes = await lane_view(session)
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return jsonify({
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"lanes": lanes,
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"fetched_at": datetime.now(UTC).isoformat(),
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})
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@workers_bp.route("/<name>", methods=["POST"])
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async def update_lane(name: str):
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"""Set a lane's cap. Stores it, then makes the live lane obey it.
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ONE field, since 2026-09-23. It used to take `slots`, `slots_cap`,
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`enabled` and `autoscale`; how many workers are running is now a
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measurement the sizing pass owns, and `enabled` is `cap > 0`.
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Two failure kinds, deliberately different statuses:
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* **400** — the value is not allowed (negative, or above what this
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container can hold). Nothing was stored. The body carries `detail`,
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which is the sentence the UI shows; a refused control with no reason
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reads as a bug.
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* **200 with `applied: false`** — the value WAS stored but could not be
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pushed, because the lane is not currently answering. Not an error: the
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sizing pass carries it within a minute, and the UI should say "saved,
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not yet live" rather than "that didn't work".
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"""
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lane = LANES_BY_NAME.get(name)
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if lane is None:
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return _bad("unknown_lane", detail=name, known=sorted(LANES_BY_NAME))
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body = await request.get_json()
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if not isinstance(body, dict):
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return _bad("invalid_body", detail="body must be a JSON object")
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if "slots_cap" not in body:
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return _bad("invalid_body", detail="give slots_cap")
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value = body["slots_cap"]
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# Rejected rather than coerced: `True` is an int in Python, and silently
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# reading it as a cap of 1 would be a control that appears to work and
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# sets something nobody asked for.
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if not isinstance(value, int) or isinstance(value, bool):
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return _bad("invalid_body", detail="slots_cap must be an integer")
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async with get_session() as session:
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try:
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result = await set_lane(session, lane, slots_cap=value)
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except LaneUpdateRefused as exc:
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return _bad("refused", detail=str(exc))
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return jsonify(result)
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