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MongoDB Connection Fix Guide

Issue: "Database connection unavailable" - 503 Error

The backend is returning a 503 error because it cannot connect to MongoDB Atlas. This is a common issue when deploying to Vercel.

Root Causes

  1. MongoDB Atlas IP Whitelist - Vercel uses dynamic IPs that need to be whitelisted
  2. Connection String Issues - Incorrect or expired credentials
  3. Network Access Settings - MongoDB Atlas firewall blocking connections
  4. Serverless Cold Starts - Connection timing out on first request

Solution Steps

Step 1: Fix MongoDB Atlas Network Access (CRITICAL)

  1. Go to MongoDB Atlas
  2. Select your cluster: Sample-Data
  3. Click on Network Access in the left sidebar
  4. Click Add IP Address
  5. Select "Allow Access from Anywhere" (0.0.0.0/0)
    • This is necessary for Vercel since it uses dynamic IPs
    • Click Confirm

Important: This is the most common cause of the 503 error!

Step 2: Verify Database User Credentials

  1. In MongoDB Atlas, go to Database Access
  2. Verify user: jenilrupapara340_db_user
  3. If the user doesn't exist or password is wrong:
    • Click Add New Database User
    • Username: jenilrupapara340_db_user
    • Password: gPaASk6ZOa4Wa44L (or create a new one)
    • Database User Privileges: Read and write to any database
    • Click Add User

Step 3: Update Connection String (if needed)

If you created a new user or changed the password, update the connection string:

Current connection string in code:

mongodb+srv://jenilrupapara340_db_user:gPaASk6ZOa4Wa44L@sample-data.vyal4lo.mongodb.net/bavadiya-realty?retryWrites=true&w=majority

To get the correct connection string:

  1. In MongoDB Atlas, click Connect on your cluster
  2. Choose Connect your application
  3. Copy the connection string
  4. Replace <password> with your actual password
  5. Replace <dbname> with bavadiya-realty

Step 4: Set Environment Variable in Vercel

  1. Go to Vercel Dashboard
  2. Select your backend project: bavadiya-realty-backend
  3. Go to Settings → Environment Variables
  4. Add or update: 
    MONGO_URI=mongodb+srv://jenilrupapara340_db_user:gPaASk6ZOa4Wa44L@sample-data.vyal4lo.mongodb.net/bavadiya-realty?retryWrites=true&w=majority
  5. Make sure it's enabled for Production, Preview, and Development
  6. Click Save

Step 5: Redeploy Backend

After making changes to environment variables:

cd backend
vercel --prod

Or trigger a redeploy from Vercel Dashboard:

  1. Go to Deployments
  2. Click the three dots on the latest deployment
  3. Click Redeploy

Step 6: Test the Connection

Test Health Endpoint

curl https://bavadiya-realty-backend.vercel.app/api/health

Expected Response (Success):

{
  "status": "healthy",
  "timestamp": "2025-11-19T13:11:00.000Z",
  "database": {
    "state": "connected",
    "stateCode": 1,
    "userCount": 1
  },
  "environment": "production"
}

If Still Failing:

{
  "status": "unhealthy",
  "timestamp": "2025-11-19T13:11:00.000Z",
  "database": {
    "state": "disconnected",
    "stateCode": 0
  },
  "environment": "production"
}

Test Login Endpoint

curl -X POST https://bavadiya-realty-backend.vercel.app/api/login \
  -H "Content-Type: application/json" \
  -d '{"username":"DharmeshBavadiya","password":"BavadiyaRealtyAdmin!2024"}'

Common Error Messages and Solutions

Error: "MongoServerSelectionError: connection timed out"

Solution: Add 0.0.0.0/0 to MongoDB Atlas Network Access (Step 1)

Error: "Authentication failed"

Solution: Verify database user credentials (Step 2)

Error: "Database connection unavailable"

Solution:

  1. Check Vercel logs: vercel logs bavadiya-realty-backend --prod
  2. Verify MONGO_URI environment variable is set correctly
  3. Ensure MongoDB cluster is not paused (check Atlas dashboard)

Error: "MongooseServerSelectionError: Could not connect to any servers"

Solution:

  1. Verify connection string format
  2. Check if MongoDB cluster is running (not paused)
  3. Verify network access settings

Checking Vercel Logs

To see detailed error messages:

# Install Vercel CLI if not already installed
npm i -g vercel

# Login to Vercel
vercel login

# View logs
vercel logs bavadiya-realty-backend --prod

Look for messages like:

  • ✅ MongoDB connected (Success)
  • ❌ MongoDB connection error (Failure - check the error message)

MongoDB Atlas Cluster Status

Make sure your cluster is not paused:

  1. Go to MongoDB Atlas Dashboard
  2. Check if cluster shows "Paused"
  3. If paused, click Resume button

Alternative: Test Connection Locally

To test if the connection string works:

cd backend
node -e "
const mongoose = require('mongoose');
mongoose.connect('mongodb+srv://jenilrupapara340_db_user:gPaASk6ZOa4Wa44L@sample-data.vyal4lo.mongodb.net/bavadiya-realty?retryWrites=true&w=majority')
  .then(() => { console.log('✅ Connected'); process.exit(0); })
  .catch(err => { console.error('❌ Error:', err.message); process.exit(1); });
"

Quick Checklist

  • MongoDB Atlas Network Access allows 0.0.0.0/0
  • Database user exists with correct credentials
  • MONGO_URI environment variable is set in Vercel
  • MongoDB cluster is not paused
  • Backend has been redeployed after env variable changes
  • Health endpoint returns "connected" status

Still Not Working?

If you've completed all steps and it's still not working:

  1. Check MongoDB Atlas Status Page: https://status.cloud.mongodb.com/
  2. Verify Vercel Status: https://www.vercel-status.com/
  3. Create a new MongoDB cluster and update the connection string
  4. Contact Support:

Success Indicators

You'll know it's working when:

  1. Health endpoint returns "state": "connected"
  2. Login endpoint returns a JWT token
  3. Frontend can successfully log in
  4. No 503 errors in browser console

Code Changes Made

The following improvements were made to handle serverless connections better:

  1. Connection Caching - Reuses existing connections in serverless environment
  2. Automatic Reconnection - Attempts to reconnect if connection is lost
  3. Better Error Messages - Detailed logging for debugging
  4. Health Check Endpoint - Easy way to verify connection status
  5. Optimized Timeouts - Faster failure detection and retry logic

Environment Variables Checklist

Make sure these are set in Vercel:

MONGO_URI=mongodb+srv://jenilrupapara340_db_user:gPaASk6ZOa4Wa44L@sample-data.vyal4lo.mongodb.net/bavadiya-realty?retryWrites=true&w=majority
JWT_SECRET=your_super_secret_jwt_key_change_this_in_production_123456789
NODE_ENV=production
DEFAULT_ADMIN_USERNAME=DharmeshBavadiya
DEFAULT_ADMIN_PASSWORD=BavadiyaRealtyAdmin!2024
DEFAULT_ADMIN_EMAIL=admin@bavadiyarealty.com
BCRYPT_ROUNDS=12
JWT_EXPIRES_IN=24h
ALLOWED_ORIGINS=https://bavadiyarealty.vercel.app
PORT=3000

Next Steps After Fix

Once the connection is working:

  1. Test login from frontend
  2. Verify data operations (create, read, update, delete)
  3. Monitor Vercel logs for any issues
  4. Consider setting up monitoring/alerts for database connectivity