How to fix Error: connect ECONNREFUSED 127.0.0.1:5432 in Node.js

# Linux/macOS
sudo systemctl status postgresql
# or
ps aux | grep postgres

# Check if PostgreSQL is listening on port 5432
sudo lsof -i :5432
# or
netstat -an | grep 5432

sudo systemctl status mongod
sudo lsof -i :27017

# Check if anything is listening on the port
lsof -i :3000
netstat -an | grep LISTEN | grep 3000

// PostgreSQL connection example
const { Client } = require('pg');

const client = new Client({
  host: '127.0.0.1',      // Verify this matches where service is running
  port: 5432,              // Verify correct port
  database: 'mydb',
  user: 'postgres',
  password: 'password'
});

client.connect()
  .then(() => console.log('Connected successfully'))
  .catch(err => {
    console.error('Connection error:', err.code, err.message);
    console.error('Attempted connection to:', client.host + ':' + client.port);
  });

// Before (may fail on Node.js 17+)
const client = new Client({
  host: 'localhost',
  port: 5432
});

// After (works reliably)
const client = new Client({
  host: '127.0.0.1',
  port: 5432
});

listen_addresses = '*'

// Listen on all interfaces
app.listen(3000, '0.0.0.0', () => {
  console.log('Server listening on all interfaces port 3000');
});

async function connectWithRetry(maxRetries = 5, delay = 2000) {
  for (let attempt = 1; attempt <= maxRetries; attempt++) {
    try {
      await client.connect();
      console.log('Connected successfully');
      return;
    } catch (err) {
      if (err.code === 'ECONNREFUSED') {
        console.log(`Connection attempt ${attempt}/${maxRetries} failed`);
        if (attempt === maxRetries) {
          throw new Error('Max retries reached. Service may not be running.');
        }
        console.log(`Retrying in ${delay}ms...`);
        await new Promise(resolve => setTimeout(resolve, delay));
      } else {
        // Different error, don't retry
        throw err;
      }
    }
  }
}

connectWithRetry()
  .catch(err => {
    console.error('Failed to connect:', err.message);
    process.exit(1);
  });

# Check firewall status
sudo ufw status

# Allow PostgreSQL port
sudo ufw allow 5432/tcp

# For local development, you can temporarily disable
sudo ufw disable

# Check if firewall is blocking the port
sudo /usr/libexec/ApplicationFirewall/socketfilterfw --getglobalstate

# Check if port is blocked
Test-NetConnection -ComputerName 127.0.0.1 -Port 5432

# docker-compose.yml
services:
  app:
    network_mode: "host"  # Access host services directly
    # Or use host.docker.internal on Docker Desktop

const client = new Client({
  host: 'host.docker.internal',  // Docker Desktop
  port: 5432
});

# docker-compose.yml
services:
  app:
    network_mode: "host"

services:
  app:
    depends_on:
      - postgres
    environment:
      DATABASE_HOST: postgres  # Use service name

  postgres:
    image: postgres:15
    ports:
      - "5432:5432"

docker run --add-host=host.docker.internal:host-gateway your-image