Deploying Juntos Applications

Juntos unlocks platforms Rails can’t reach—and works everywhere JavaScript runs.

Table of Contents

• Deploying Juntos Applications
  • Sweet Spots
  • Also Works
  • Quick Comparison
  • Choosing a Target
  • Default Target Inference
  • Hybrid Development
    • Recommended Pairings
    • Example Configuration
    • Offline-First Browser Apps
  • Database Setup Guides

Sweet Spots

These targets require transpilation. Rails can’t run here; Juntos can:

Also Works

For traditional hosting, Juntos works but Rails does too. Reasons to choose Juntos on a server runtime:

• npm ecosystem — access to JavaScript libraries not available in Ruby
• Event-driven model — JavaScript’s async I/O may suit some workloads better than Ruby’s Global VM Lock (GVL)
• Unified codebase — one codebase across browser, edge, and server

Quick Comparison

Choosing a Target

Choose Browser if:

• Your app works offline or local-first
• Data stays on the user’s device
• You want zero infrastructure
• Rails can’t do this

Choose Vercel, Deno Deploy, or Cloudflare if:

• You want global edge distribution
• You need auto-scaling and pay-per-request
• You want fast cold starts (~5-50ms)
• Rails can’t do this

Choose Fly.io if:

• You need native WebSocket support (Turbo Streams without Pusher)
• You want CLI-driven workflow (no dashboard copying)
• You want managed Postgres with automatic failover
• Rails works here too—but Juntos + MPG provides a streamlined CLI workflow

Choose Node.js, Bun, or Deno if:

• You need npm packages not available in Ruby
• Your workload benefits from JavaScript’s event-driven async model
• You want one codebase across browser, edge, and server
• Rails works here too—but Juntos has advantages

Choose Capacitor if:

• You want native iOS/Android apps
• You need device APIs (camera, GPS, push notifications)
• You want App Store/Google Play distribution
• Rails can’t do this

Choose Electron if:

• You want native desktop apps (macOS, Windows, Linux)
• You need OS integration (system tray, global shortcuts, file system)
• You want distributable installers (DMG, EXE, AppImage)
• Rails can’t do this

Choose Tauri if:

• You want lightweight desktop apps (~3-10MB vs Electron’s ~150MB)
• Lower memory usage is important
• You’re comfortable with Rust for custom native features
• You want the smallest possible bundle size
• Rails can’t do this

Default Target Inference

When you don’t specify a target, Juntos infers it from your database:

bin/juntos up -d dexie      # → browser
bin/juntos up -d sqlite     # → node
bin/juntos up -d neon       # → vercel
bin/juntos up -d d1         # → cloudflare
bin/juntos up -d mpg        # → fly

Override with -t:

bin/juntos up -t node -d neon   # Force Node.js with Neon

Hybrid Development

You don’t need to hit remote databases during development. Use the familiar config/database.yml pattern—a local database for development, a cloud database for production.

Recommended Pairings

Example Configuration

# config/database.yml
development:
  adapter: sqlite
  database: db/development.sqlite3

production:
  adapter: d1
  database: myapp_production

# Development: instant feedback, no cloud round-trips
bin/juntos up -d sqlite

# Production: deploy to Cloudflare with D1
bin/juntos deploy -d d1

The SQL dialect matches between SQLite and D1, so your migrations and queries work in both environments.

Offline-First Browser Apps

The browser target enables offline-first applications that sync with a Rails backend:

1. Browser app — runs entirely client-side with IndexedDB (Dexie)
2. Rails API — traditional server for sync and shared data
3. Sync on reconnect — browser app treats Rails as an API when connectivity returns

This pattern works well for:

• Mobile apps in spotty connectivity
• Field data collection
• Event scoring/judging systems
• Any scenario where the app must work without internet

# Same models power both apps
development:
  adapter: dexie      # Browser app
  database: myapp_dev

production:
  adapter: pg         # Rails API backend
  url: <%= ENV['DATABASE_URL'] %>

Database Setup Guides

For detailed setup instructions, see the Database Overview:

• Neon — Serverless PostgreSQL
• Turso — SQLite at the edge
• PlanetScale — Serverless MySQL
• Supabase — Full backend platform