app/docs/concepts/runs.md

Runs: pipelines that finish

A flow that automates a house never ends — a value arrives, nodes fire, and it waits for the next one. A research pipeline is the other shape: parameters go in, stages execute in order, and at some point it is done and has produced something worth keeping. Fluksio calls the second one a run, and it is the same engine either way.

This is what makes Fluksio usable where Kedro, MLflow or ClearML would be: a run has parameters that identify it, a result, per-step metrics, artifacts and a place in a queryable history — without a second server, and without paying a project bootstrap on every execution.

A batch flow

Set mode: "batch" on the flow and name the messages its result should hold:

{
  "name": "train_polymer_gnn",
  "mode": "batch",
  "outputs": ["final_loss", "report"],
  "inputs": [
    {"spec": {"name": "lr", "dtype": "float"}, "initial": 0.1},
    {"spec": {"name": "steps", "dtype": "int"}, "initial": 3000}
  ],
  "nodes": [{"id": "train", "timeout": 7200, "device": "gpu", "...": "..."}]
}

A batch flow is built and validated like any other — it appears on the canvas, its ports are type-checked — but it is never activated: no subscriptions, no schedules, no webhooks. It runs when a run asks it to, and not otherwise.

Its inputs are its parameters. A run supplies values for them; anything it does not supply keeps the declared initial value.

One thing a batch flow may not do is rate-limit a port (interval). A rate limit holds a value back for a timer to release, and a run has no timer — the value would be dropped rather than delayed, so submitting is refused instead.

Submitting

curl -X POST $FLUKSIO/runs/flows/train_polymer_gnn \
     -H "Authorization: Bearer $TOKEN" -H 'Content-Type: application/json' \
     -d '{"params": {"lr": 0.3, "steps": 4000}, "seed": 7}'

The answer is immediate and the run is queued; a training run is measured in hours, so nothing waits for it. Poll GET /api/v1/runs/{id} for its status, result, per-node record and artifacts.

Wrong parameters are refused before anything executes — an undeclared name, or a value of the wrong type, comes back as a 422 naming the problem.

Sweeps

An ensemble is the same parameters at different seeds; a grid search is the parameters spread out. Both are one call, and the caller builds the list:

curl -X POST $FLUKSIO/runs/flows/train_polymer_gnn/sweep \
     -H "Authorization: Bearer $TOKEN" -H 'Content-Type: application/json' -d '{
  "runs": [{"params": {"lr": 0.1}, "seed": 1}, {"params": {"lr": 0.3}, "seed": 1}]
}'

From a terminal that is fluksio sweep train_polymer_gnn --param lr=0.1,0.3, which builds the product of the lists you give it and posts the same call.

They share a group_id, so GET /api/v1/runs?group=… is the sweep, and they execute in parallel. That is safe because each run has a state backend of its own: message names are global keys, so two runs of one flow would otherwise overwrite each other's values. They do not.

Producing values before you are finished

A training loop has numbers worth keeping long before it has a result. Those numbers are outputs, not logs: a node declares a port for them and produces them over time, which in Python is a generator.

def process(lr, steps):
    loss = 1.0
    for _ in range(steps):
        loss = train_one_step(lr)
        yield {"loss": loss}          # published now, on the `loss` port
    return {
        "weights": fluksio.save_artifact(dump(model), "weights.npz"),
        "final_loss": loss,
    }

Mark the port it streams on, so the flow says what it does:

{"name": "loss", "dtype": "float", "stream": true}

Every yield is published the instant it happens — same port, same type check, same place on the canvas as any other value. Whatever the generator returns is the node's result, and is what downstream nodes read. If you never return, the last thing you yield is the result instead.

This is the whole reason the framework does not have a logging API. A metric that escapes through log_metric() is undeclared: invisible to validation, absent from the canvas, and stored somewhere the graph knows nothing about. A metric that leaves through a port is a message — so a chart binds to it directly, a downstream node can consume it, and the run keeps its series without anyone asking.

Where a yield cannot reach — the value comes from inside somebody else's callback, and they call you rather than the other way round — fluksio.emit writes the same ports the same way:

import fluksio


def process():
    model.fit(callbacks=[LambdaCallback(
        on_epoch_end=lambda epoch, logs: fluksio.emit(loss=logs["loss"])
    )])
    return {"weights": ...}

What a run does with them

Every number a node emits is kept as the run's series, stepped by the count of emissions on that message. Read one back with GET /api/v1/runs/{id}/metrics?name=<flow>.loss — or leave name off for every series the run kept — or compare runs:

GET /api/v1/runs/series/compare?ids=<a>,<b>,<c>&metric=<flow>.loss

That answers in the series shape a chart widget already draws, so three training curves side by side is a widget binding. During a run the values also arrive live on the flow socket, so a chart bound to the port fills in as the training goes.

A streaming port may set interval to thin out what reaches the canvas — the run's history still keeps every value, because the interval is asking for the display not to be flooded, not for the curve to have holes in it.

Emitting has a second effect: a node's timeout measures silence, not duration. A node that yields every few seconds can run for hours under a timeout of 300; one that says nothing for longer than its timeout is killed. There is no timeout unless one is set — a training node that reports nothing is usually working — so set timeout where going quiet means stuck, at how long the node may plausibly be.

In a live flow, an emission also wakes whatever is downstream of it, exactly as a subscriber publishing does. In a run it does not: a run's graph is scheduled once, and three thousand mid-node cascades would leave "the run has finished" with nothing to mean.

Artifacts

Bytes never travel as a message. save_artifact writes them to a content-addressed store and returns a small reference — digest, size, media type, name — which is what an artifact-typed port carries:

def process(weights):          # requires: weights, dtype "artifact"
    path = fluksio.load_artifact(weights)
    ...

Because the address is the content's hash, a sweep whose fifty configs share one preprocessed input stores it once, and a reference stays valid wherever the store is reachable from. Artifacts a run produced are listed on it and downloadable at GET /api/v1/artifacts/{digest}.

Stage caching

A run mostly does not redo what an earlier one already did. Before a node executes it is fingerprinted — a sha256 over its source, its settings and the values it is about to read — and if some earlier run of that same fingerprint finished, what that one returned is restored into this run's state and the node is skipped. It is recorded with the status cached and a duration of zero, and its artifacts are listed on the new run as well, so they stay downloadable from either.

The settings go into the key raw, so a secret contributes its {"$secret": name} reference and never its value. An artifact input counts as its content digest: the same bytes under a different filename are the same input. Each node on a run carries the cache_key it was looked up by.

The run history is the cache; there is no second store. A node's returned outputs are kept on its run record as canonical JSON, up to 256000 characters — a node returning more than that is simply not cacheable that run. An entry whose artifact bytes have since left the store is a miss, not an error.

Only python nodes are cached, and by default all of them are. A built-in node type or a connector node has side effects and no source to fingerprint, so neither is ever a candidate. Turn it off for one node with @node(..., cache=False) — the flow document carries it as cache, so the canvas and the API can change it too — or for one run with fluksio run --no-cache, fluksio sweep --no-cache, or "no_cache": true in the submission body.

What a cached node does not bring back is what it emitted on the way. Its returned outputs are restored; the values it published mid-execution are not, because those were the story of an execution that is not happening this time. So a skipped training node contributes no loss curve to the new run — if you want the curve, that run has to actually train.

Objects that cannot be serialized

A live model, a DataLoader, a JAX-compiled function — these do not cross a node boundary, and no framework flag will make them. There are exactly two patterns, and they are both deliberate:

• Keep them in one node. Stages that must share live memory are one node. Building the model and training it is one stage; the fact that Kedro would make them two nodes is Kedro's problem, not a structure worth reproducing.
• Cross at a checkpoint. Save what matters as an artifact and rebuild from it on the other side. That is the boundary that also survives the next node running on a different machine.

Running a node somewhere else

A node that needs a GPU declares the label of the machine that has one:

{"id": "train", "device": "gpu", "device_policy": "require", "timeout": 7200}

A worker on that machine dials out to the engine, because the engine generally cannot reach it — different network, no inbound route — and because nothing should expose Redis across hosts. Install it on the box, mint it a token, and start it:

curl -X POST $FLUKSIO/workers/tokens -d '{"name": "gpu-dev"}'   # once, as an admin

pip install fluksio-worker

fluksio-worker \
  --url wss://api.example.com/api/v1/workers/attach \
  --token "$FLUKSIO_WORKER_TOKEN" \
  --labels gpu,cuda12 \
  --python /opt/torch-venv/bin/python

fluksio-worker is its own distribution — the agent, the node runner, and websockets. Nothing of the engine, so a GPU box does not install a database driver to run a training step. Where pip is not an option, the two files still work copied into one directory and run with python agent.py …; the engine serves the runner at GET /api/v1/workers/runtime.

--python is the interpreter node code runs on, which is how the GPU box keeps its CUDA wheels without the engine ever installing them. The node's source travels with every call, so nothing has to be deployed there.

A few consequences worth knowing:

• import fluksio inside a node is the worker's own reporter — emit, save_artifact, load_artifact — installed before the node's code runs, so the installed fluksio package (if the box has one) never shadows it.
• A node bound to a device is compiled on that machine. A node importing torch is correct on the GPU box and a missing module on the engine, so checking it on the engine would fail a node that is fine.
• If nothing carrying the label is attached, the run stays queued and says what it is waiting for. Submit first, switch the GPU box on later.
• Cancelling a run kills what it is executing, there or here, and leaves other runs of the same node alone.
• If the worker disappears mid-call, the run fails in seconds with worker went away mid-call rather than waiting out its timeout.
• device_policy: "prefer" runs locally when no such worker is attached; "require" (the default) waits for one.

Durability

Submitting journals the run to a Redis stream of its own, separate from the one the automations use — a burst of five hundred sweep runs must not stand between a house and its heating. An engine that is down when a run is submitted picks it up when it starts.

From the moment a run is claimed, its database row is the record and the queue is finished with it. Redelivering two hours of training because an acknowledgement was late is not recovery; instead a running run refreshes a lease, and one whose lease goes stale is marked abandoned — which is what a run whose engine was killed mid-training becomes.

Looking at what ran

The Runs screen is the experiment log: every run newest-first, filtered by flow, by status, or down to one sweep. A sweep is worth filtering to — the table then draws a column per parameter that actually varied, which is what makes fifty runs of one flow readable.

Tick two or more and their curves go side by side. That comparison is the address, so a link to it is a link someone else can open.

One run in full is params, the per-node record with its logs and traceback, the artifacts it made, its metrics and its result.

A dashboard, read against runs

A run records values under the same names a dashboard binds to — a run of study writes study.loss — so a dashboard is already a way of looking at one. Open in dashboard from a run or a comparison opens any dashboard with ?runs=a,b,c on it, and the widgets resolve from those runs instead of from the live engine: each chart draws a line per run, the tiles that show one number show the first, and the controls go quiet because there is nothing left to publish to.

Nothing about the dashboard is specific to runs. The page built to watch a training run happen is the page that shows the finished ones.

If a flow has no dashboard yet, the same menu offers to build one from what the flow declares — a chart per streaming port, a tile per output:

POST /api/v1/dashboards/from-flow/study

It publishes study_results and is an ordinary dashboard afterwards; editing it is how it stops being generic.

A tile that always shows the last few

The other direction is a chart pinned to runs rather than a page opened against them, which is what a panel over a bench wants. Set a chart's source to Runs, name the metric, and pick either the latest N of a flow, one sweep, or specific runs. It re-reads on its own and whenever a run finishes.

When a run draws nothing

A node restored from the stage cache replays no emissions — a cache hit returns what the node returned, not what it emitted on the way. So a run that reused an earlier one has a result and an empty curve, and the chart says so rather than looking broken.

What this costs, compared

The repository ships a benchmark that measures submitting a run against a Kedro project doing the same nothing:

fluksio — submit accepted     median   15.3 ms
          submit -> result    median   60.8 ms
kedro   — kedro run           median 1109.5 ms

The difference is not the orchestration; it is that Fluksio does not boot a project per run. The engine is already up, and the workers already have the node's code compiled. On a 510-run sweep, that gap is about nine minutes of pure startup that never happens.

See also

• Getting started: data science — the same material as a first setup
• Writing node code — generators, fluksio.emit, artifacts
• Remote workers — attaching the machine with the GPU
• The HTTP API — every endpoint used above