Modal Scheduled Jobs

Reviewed against Modal 1.6.0 and official scheduling documentation. Schedules were constructed locally only; these application-specific job bodies are illustrative and were not deployed or triggered.

Overview

Modal supports running functions automatically on a schedule, either using cron syntax or fixed intervals. Deploy scheduled functions with modal deploy and they run unattended in the cloud.

Schedule Types

modal.Cron

Standard cron syntax — stable across deploys:

import modal

app = modal.App("scheduled-tasks")

# Daily at 9 AM UTC
@app.function(schedule=modal.Cron("0 9 * * *"))
def daily_report():
    generate_and_send_report()

# Every Monday at midnight
@app.function(schedule=modal.Cron("0 0 * * 1"))
def weekly_cleanup():
    cleanup_old_data()

# Every 15 minutes
@app.function(schedule=modal.Cron("*/15 * * * *"))
def frequent_check():
    check_system_health()

Cron Syntax Reference

┌───────────── minute (0-59)
│ ┌───────────── hour (0-23)
│ │ ┌───────────── day of month (1-31)
│ │ │ ┌───────────── month (1-12)
│ │ │ │ ┌───────────── day of week (0-6, Sun=0)
│ │ │ │ │
* * * * *

modal.Period

Fixed interval — resets on each deploy:

# Every 5 hours
@app.function(schedule=modal.Period(hours=5))
def periodic_sync():
    sync_data()

# Every 30 minutes
@app.function(schedule=modal.Period(minutes=30))
def poll_updates():
    check_for_updates()

# Every day
@app.function(schedule=modal.Period(days=1))
def daily_task():
    ...

modal.Period resets its timer on each deployment. If you need a schedule that doesn't shift with deploys, use modal.Cron. Cron defaults to UTC; use modal.Cron("0 9 * * *", timezone="America/New_York") for a named timezone. Scheduled Functions must be callable with no required arguments. Make repeated scheduled writes idempotent; redeployment and retries are not exactly-once guarantees.

Deploying Scheduled Functions

Schedules only activate when deployed:

modal deploy script.py

modal run and modal serve do not activate schedules.

Monitoring

• View scheduled runs in the Apps section of the Modal dashboard
• Each run appears with its status, duration, and logs
• Use the "Run Now" button on the dashboard to trigger manually

Management

• Schedules cannot be paused — remove the schedule and redeploy to stop
• To change a schedule, update the schedule parameter and redeploy
• To stop entirely, either remove the schedule parameter or run modal app stop <name>

Common Patterns

ETL Pipeline

@app.function(
    schedule=modal.Cron("0 2 * * *"),  # 2 AM UTC daily
    secrets=[modal.Secret.from_name("db-creds")],
    timeout=7200,
)
def etl_pipeline():
    import os
    data = extract(os.environ["SOURCE_DB_URL"])
    transformed = transform(data)
    load(transformed, os.environ["DEST_DB_URL"])

Model Retraining

@app.function(
    schedule=modal.Cron("0 0 * * 0"),  # Weekly on Sunday
    gpu="H100",
    volumes={"/data": data_vol, "/models": model_vol},
    timeout=86400,
)
def retrain():
    model = train_on_latest_data("/data/training/")
    torch.save(model.state_dict(), "/models/latest.pt")
    model_vol.commit()

Health Checks

@app.function(
    image=modal.Image.debian_slim().uv_pip_install("requests"),
    schedule=modal.Period(minutes=5),
    secrets=[modal.Secret.from_name("slack-webhook")],
)
def health_check():
    import os, requests
    status = check_all_services()
    if not status["healthy"]:
        response = requests.post(os.environ["SLACK_URL"], json={"text": f"Alert: {status}"}, timeout=30)
        response.raise_for_status()

The webhook URL is read from a Modal Secret (SLACK_URL), not hardcoded or taken from untrusted input. Keep notification endpoints in Secrets and avoid POSTing to URLs constructed from user-supplied data.