Fix MongoDB Connection Refused Error

Common Error Messages:
• "Error: couldn't connect to server 127.0.0.1:27017"
• "MongoDB connection refused"
• "Error connecting to MongoDB: connect ECONNREFUSED"

What This Error Means

The "connection refused" error occurs when your MongoDB client cannot establish a connection to the MongoDB server. This typically happens when:

The MongoDB service (mongod) is not running
MongoDB is running on a different port than expected
Firewall rules are blocking the connection
The MongoDB configuration is incorrect

Immediate Fix

Step 1: Check MongoDB Service Status

First, verify if MongoDB is actually running:

# On Ubuntu/Debian:
sudo systemctl status mongod

# On CentOS/RHEL:
sudo systemctl status mongod

# On macOS with Homebrew:
brew services list | grep mongodb
        

Step 2: Start MongoDB Service

If MongoDB is not running, start it:

# On Ubuntu/Debian:
sudo systemctl start mongod
sudo systemctl enable mongod  # Auto-start on boot

# On CentOS/RHEL:
sudo systemctl start mongod
sudo systemctl enable mongod

# On macOS with Homebrew:
brew services start mongodb-community

# Manual start (if service commands don't work):
sudo mongod --config /etc/mongod.conf
        

Step 3: Check Port and Configuration

Verify MongoDB is listening on the correct port:

# Check what's listening on port 27017:
sudo netstat -tlnp | grep :27017

# Or using ss command:
sudo ss -tlnp | grep :27017

# Check MongoDB configuration:
cat /etc/mongod.conf
        

Step 4: Test Connection

# Test connection locally:
mongo --host 127.0.0.1 --port 27017

# Or with modern MongoDB shell:
mongosh "mongodb://127.0.0.1:27017"
        

Root Cause

1. Service Not Running

The most common cause is that the MongoDB daemon (mongod) has stopped or failed to start. This can happen due to:

System restart without auto-start configured
Resource constraints (disk space, memory)
Configuration file errors
Permission issues on data directory

2. Configuration Issues

Check your /etc/mongod.conf file for common issues:

# Common configuration problems:
net:
  port: 27017
  bindIp: 127.0.0.1  # Change to 0.0.0.0 for external access

storage:
  dbPath: /var/lib/mongo  # Ensure this directory exists and has correct permissions

systemLog:
  destination: file
  logAppend: true
  path: /var/log/mongodb/mongod.log
        

3. Firewall Blocking Connections

If connecting from another machine, check firewall rules:

# Ubuntu/Debian (ufw):
sudo ufw allow 27017

# CentOS/RHEL (firewalld):
sudo firewall-cmd --permanent --add-port=27017/tcp
sudo firewall-cmd --reload

# Check if port is blocked:
telnet your-server-ip 27017
        

How to Prevent This

1. Enable Auto-Start

sudo systemctl enable mongod

2. Monitor Service Health

Set up monitoring to alert when MongoDB goes down:

# Simple health check script:
#!/bin/bash
if ! pgrep mongod > /dev/null; then
    echo "MongoDB is down!" | mail -s "MongoDB Alert" admin@yourcompany.com
    sudo systemctl start mongod
fi
            

3. Log Rotation

Ensure log files don't fill up disk space:

# Add to /etc/logrotate.d/mongod:
/var/log/mongodb/*.log {
    daily
    missingok
    rotate 52
    compress
    notifempty
    create 644 mongod mongod
    postrotate
        /bin/kill -SIGUSR1 `cat /var/lib/mongo/mongod.lock 2> /dev/null` 2> /dev/null || true
    endscript
}
            

Security Note: If you change bindIp from 127.0.0.1 to 0.0.0.0 to allow external connections, ensure you have proper authentication and firewall rules in place to prevent unauthorized access.

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