servectl

Serve a model file over HTTP in one command, with health and Prometheus metrics built in.

You have a trained model on disk and you want it behind an HTTP endpoint to try it, wire it into a demo, or scrape its metrics, without writing a FastAPI app each time. servectl loads the artifact and serves it: a typed /predict, a /health check, and a Prometheus /metrics endpoint, ready to scrape.

$ servectl serve model.joblib --port 8000
servectl: serving 'model' on http://127.0.0.1:8000

$ curl -s localhost:8000/predict -d '{"instances": [[5.1, 3.5, 1.4, 0.2]]}'
{"predictions": [0]}

Install

$ pip install servectl                 # from PyPI, once released
$ pip install git+https://github.com/jmweb-org/servectl   # latest, available now

Loads any joblib/pickle artifact that exposes a scikit-learn-style predict (and optionally predict_proba).

Usage

$ servectl serve model.joblib                 # serve on 127.0.0.1:8000
$ servectl serve model.joblib --host 0.0.0.0 --port 9000
$ servectl info model.joblib                  # inspect without serving

Endpoints

The request body is validated: instances must be a non-empty list of equal- length numeric rows. A bad request returns 400 with a message, not a stack trace.

Metrics

The /metrics endpoint exposes:

• servectl_requests_total{endpoint, outcome} — request count per endpoint and ok/error.
• servectl_predictions_total — total prediction instances served.
• servectl_predict_seconds — prediction latency histogram.

Each server uses its own registry, so the counters reflect only that process.

Prometheus scrape example

If servectl is running on port 8000, add a scrape job like this to prometheus.yml:

scrape_configs:
  - job_name: "servectl"
    metrics_path: "/metrics"
    static_configs:
      - targets: ["localhost:8000"]

For multiple model servers, give each target a stable label so dashboards can separate them:

scrape_configs:
  - job_name: "servectl"
    metrics_path: "/metrics"
    static_configs:
      - targets: ["iris-api:8000"]
        labels:
          model: "iris"
      - targets: ["churn-api:8000"]
        labels:
          model: "churn"

Grafana panel queries

Use these PromQL queries for a basic dashboard:

For per-model latency when you added a model scrape label, group the histogram by both model and le:

histogram_quantile(
  0.95,
  sum by (model, le) (rate(servectl_predict_seconds_bucket[5m]))
)

Scope

servectl is for trying a model, demos, and internal services. It does no authentication, batching, or autoscaling. For a hardened deployment, put it behind a reverse proxy or use a full serving stack; for a quick, observable endpoint from a model file, this is one command.

License

MIT. See LICENSE.