How to use multiple runtimes in Replit

1# replit.nix — Python + Node.js + Go
2{ pkgs }: {
3  deps = [
4    pkgs.python310
5    pkgs.python310Packages.pip
6    pkgs.nodejs-20_x
7    pkgs.go_1_21
8    pkgs.pkg-config
9  ];
10}

1# Recommended directory structure:
2# project-root/
3# ├── .replit
4# ├── replit.nix
5# ├── backend/
6# │   ├── main.py
7# │   ├── requirements.txt
8# │   └── ...
9# ├── frontend/
10# │   ├── package.json
11# │   ├── src/
12# │   └── ...
13# └── shared/
14#     └── config.json

1# Install Python dependencies:
2cd backend && pip install -r requirements.txt && cd ..
3
4# Install Node.js dependencies:
5cd frontend && npm install && cd ..
6
7# Or automate with onBoot in .replit:
8# onBoot = "cd backend && pip install -r requirements.txt && cd ../frontend && npm install"

1# .replit — multi-process run command
2entrypoint = "backend/main.py"
3
4run = "cd backend && python main.py & cd frontend && npm run dev & wait"
5
6onBoot = "cd backend && pip install -r requirements.txt && cd ../frontend && npm install"
7
8[nix]
9channel = "stable-24_05"
10
11[[ports]]
12localPort = 5000
13externalPort = 80
14
15[[ports]]
16localPort = 3000
17externalPort = 3000
18
19[run.env]
20FLASK_ENV = "development"
21NODE_ENV = "development"

1# .replit — port mapping for Python backend (5000) and React frontend (3000)
2[[ports]]
3localPort = 5000
4externalPort = 80
5
6[[ports]]
7localPort = 3000
8externalPort = 3000
9
10# backend/main.py — Flask on port 5000:
11from flask import Flask
12app = Flask(__name__)
13
14@app.route('/api/hello')
15def hello():
16    return {'message': 'Hello from Python!'}
17
18if __name__ == '__main__':
19    app.run(host='0.0.0.0', port=5000)
20
21# frontend/vite.config.js — proxy API calls to Python backend:
22export default {
23  server: {
24    host: '0.0.0.0',
25    port: 3000,
26    proxy: {
27      '/api': 'http://localhost:5000'
28    }
29  }
30};

1# .replit — deployment configuration for multi-runtime
2[deployment]
3build = ["sh", "-c", "cd backend && pip install -r requirements.txt && cd ../frontend && npm install && npm run build"]
4run = ["sh", "-c", "cd backend && python main.py"]
5deploymentTarget = "cloudrun"
6
7# In this setup, the Python backend serves the built frontend:
8# backend/main.py addition:
9import os
10from flask import Flask, send_from_directory
11
12app = Flask(__name__, static_folder='../frontend/dist')
13
14@app.route('/', defaults={'path': ''})
15@app.route('/<path:path>')
16def serve(path):
17    if path and os.path.exists(os.path.join(app.static_folder, path)):
18        return send_from_directory(app.static_folder, path)
19    return send_from_directory(app.static_folder, 'index.html')