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Deployment Guide

Deploy WATFlow workflows to Modal for scheduled serverless execution.

Prerequisites

  1. Modal account - Sign up at modal.com (free tier available)
  2. Workflow tested locally - Run wat run <workflow> first
  3. API keys configured - All required keys in your .env file

Quick Start

# Install Modal (first time only)
uv pip install modal

# Authenticate with Modal (opens browser)
modal setup

# Deploy your workflow
wat deploy my-workflow

What Happens During Deployment

wat deploy my-workflow
  │
  ├─ 1. Generates modal_app.py
  │     (Container configuration)
  │
  ├─ 2. Creates Modal secret from .env
  │     (API keys stored securely)
  │
  ├─ 3. Deploys to Modal
  │     (All files copied to container)
  │
  └─ 4. Prints success with dashboard URL

Files Deployed to Modal

LOCAL                             MODAL CONTAINER
my-workflow/                      /root/my-workflow/
├── main.py            ────────►  ├── main.py
├── config.yaml        ────────►  ├── config.yaml
├── requirements.txt   ────────►  ├── requirements.txt
├── tools/             ────────►  ├── tools/
├── workflows/         ────────►  ├── workflows/
├── credentials.json   ────────►  ├── credentials.json
├── token.json         ────────►  ├── token.json
│                                 │
└── .env               ──secret──►  (env vars injected at runtime)

The .env file is NOT copied directly - its contents become a Modal Secret for security.

Schedule Configuration

Add a deployment section to your workflow's config.yaml:

deployment:
  platform: modal
  schedule: weekly          # daily, weekly, or monthly
  schedule_day: sunday      # For weekly: monday-sunday
  schedule_time: "08:00"    # UTC time (24-hour format)
  timeout: 1800             # Optional: seconds (default 1800)

Omit schedule fields for on-demand only (no automatic runs).

Commands Reference

Command Description
wat deploy <name> Deploy workflow to Modal
wat deploy <name> --dry-run Generate modal_app.py without deploying
modal run modal_app.py::run_workflow Run deployed workflow once
modal logs View workflow logs

After Deployment

Updating a Deployed Workflow

Simply run wat deploy <name> again. It will:

  • Regenerate modal_app.py
  • Update the Modal secret with current .env values
  • Redeploy with the latest code

Troubleshooting

Modal CLI not installed

uv pip install modal

Modal CLI not authenticated

modal setup

Deployment fails

Check the Modal dashboard for error logs. Common issues:

  • Missing dependencies in requirements.txt
  • Invalid Python syntax in tools
  • Missing environment variables

Secret not found

Ensure your .env file exists and contains valid KEY=value pairs.

Cost

Modal pricing is based on compute time. A typical workflow running weekly:

  • ~30 seconds of compute time per run
  • Well within free tier limits

See Modal pricing for details.