Add deployable Express backend for Render with Vercel CORS integration

[Copilot]

Adds a standalone Node.js/Express backend under backend/ ready to deploy on Render, configured to accept requests from the already-deployed frontend at https://crowd-monitoring-hack2skill.vercel.app.

New files: backend/

• server.js — Express server with:
  • CORS allowlist: Vercel frontend + localhost:3000/5173
  • GET /health — Render health check endpoint
  • GET / — base route
  • POST /api/predict — stub endpoint echoing payload + sample density result; replace body with real model logic
  • JSON 404 catch-all
• package.json — npm start → node server.js; deps: express, cors, dotenv
• render.yaml — Render web service config (rootDir: backend, free plan, healthCheckPath: /health)
• .env.example — PORT=10000 + commented secret placeholders

Frontend integration

Set VITE_API_BASE_URL in Vercel project settings to the Render service URL, then call:

const API_BASE = import.meta.env.VITE_API_BASE_URL;
await fetch(`${API_BASE}/api/predict`, { method: "POST", body: JSON.stringify(payload) });

README

Added Render Backend Deployment section covering deploy steps, Vercel env var setup, and local dev instructions.

Original prompt

Create a pull request in repository erenyeager101/Crowd_monitoring to prepare a deployable backend for Render and connect it with the already deployed frontend at https://crowd-monitoring-hack2skill.vercel.app/.

Implement the following changes:

1. Add a new backend/ directory with the files below.

2. Create backend/package.json with:

   • name crowd-monitoring-backend
   • main server.js
   • scripts: start runs node server.js
   • dependencies: express, cors, dotenv

3. Create backend/server.js as a single Express server file that includes:

   • dotenv setup
   • PORT from env with default 10000
   • JSON body parsing
   • CORS configured to allow:
     • https://crowd-monitoring-hack2skill.vercel.app
     • http://localhost:3000
     • http://localhost:5173
   • GET /health returning 200 JSON status payload
   • GET / returning a simple running message JSON
   • POST /api/predict stub endpoint that echoes request payload and returns a sample result object
   • 404 JSON handler

4. Create backend/.env.example including:

   • PORT=10000
   • commented placeholders for other secrets

5. Create backend/render.yaml with a web service config:

   • type: web
   • env: node
   • rootDir: backend
   • buildCommand: npm install
   • startCommand: npm start
   • healthCheckPath: /health
   • free plan

6. Update repository documentation (README or backend README) with concise deployment instructions:

   • how to deploy backend on Render
   • where to set frontend env var to backend URL (Vercel)
   • expected API base URL usage pattern

Acceptance criteria:

• Backend runs locally with npm start from backend/.
• /health returns successful JSON response.
• CORS permits the deployed frontend domain.
• Render can deploy using the provided config.
• PR includes all new files under backend/ and docs update.

The following is the prior conversation context from the user's chat exploration (may be truncated):

User: Prepare the backend of proj3ct to be depoyed on render

Assistant: I can help with that.
To proceed, I need one clarification before I make any repo changes:

Do you want me to prepare the backend in this repository: erenyeager101/Crowd_monitoring?

Also, please confirm:

1. Backend stack (Node/Express, Django, Flask, FastAPI, etc.)
2. Deploy target on Render (Web Service, Background Worker, or both)
3. Whether you want me to:
   • create/update render.yaml
   • add start/build scripts
   • add env var template (.env.example)
   • update README with deploy steps

Once you confirm, I’ll generate the exact changes needed for Render deployment.

User: Prepare the backend of proj3ct to be depoyed on render as frontned is already deployed on https://crowd-monitoring-hack2skill.vercel.app/ and we need backend to host on render so prepare and add all files to a backend folder with a single server file that i will host... then connect these both so it runs properly

Assistant: Great — I can do this, but I still need one required detail before I can safely make repo-specific changes:

Please confirm the repository name in owner/repo format where I should add the backend/ folder.
From context, I think it is erenyeager101/Crowd_monitoring — please reply “yes” (or provide the correct one).

Also confirm the backend runtime you want for the single server file:

• Node.js (Express) (recommended for quick Render deploy), or
• something else.

Once you confirm, I’ll give you:

1. exact backend/ structure,
2. single-server backend code,
3. Render config/start command,
4. frontend-to-backend connection steps for your Vercel app (https://crowd-monitoring-hack2skill.vercel.app/).

User: Yes

Assistant: Perfect. I’ll set it up assuming erenyeager101/Crowd_monitoring and a Node.js + Express single-file backend in backend/server.js.

What to add

Create these files:

backend/
  package.json
  server.js
  .env.example
  render.yaml

1) backend/package.json

{
  "name": "crowd-monitoring-backend",
  "version": "1.0.0",
  "description": "Backend for Crowd Monitoring app",
  "main": "server.js",
  "type": "commonjs",
  "scripts": {
    "start": "node server.js"
  },
  "dependencies": {
    "cors": "^2.8.5",
    "dotenv": "^16.4.5",
    "express": "^4.19.2"
  }
}

2) backend/server.js

const express = require("express");
const cors = require("cors");
const dotenv = require("dotenv");

dotenv.config();

const app = express();
const PORT = process.env.PORT || 10000;

// Allow your deployed frontend + local dev
const allowedOrigins = [
  "https://crowd-monitoring-hack2skill.vercel.app",
  "http://localhost:3000",
  "http://localhost:5173"
];

app.use(
  cors({
    origin: function (origin, callback) {
      // Allow requests with no origin (Postman/mobile apps/curl)
      if (!origin) return callb...

</details>



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Project	Deployment	Actions	Updated (UTC)
crowd-monitoring	Error		Mar 22, 2026 5:11am
crowd-monitoring-hack2skill	Ready	Preview, Comment	Mar 22, 2026 5:11am
vite	Error		Mar 22, 2026 5:11am