Fix MongoServerError: connect ECONNREFUSED 127.0.0.1:27017

TL;DR

ECONNREFUSED on port 27017 means your app tried to reach MongoDB, but the service isn't running — nothing is listening on that port. Nine times out of ten, one command is all you need:

# Linux (systemd)
sudo systemctl start mongod

# macOS (Homebrew)
brew services start mongodb-community

# Windows
net start MongoDB

Root Cause

ECONNREFUSED is a TCP-level error. The OS actively rejected the connection — the port is closed. That happens for a few reasons:

• The mongod process isn't running
• MongoDB is listening on a different port or bind address
• A firewall is blocking port 27017
• The data directory has wrong permissions, preventing mongod from starting
• MongoDB crashed on startup (the logs will say why)

Step 1 — Check if mongod is running

# Linux / macOS
ps aux | grep mongod

# Or check the service status
sudo systemctl status mongod

A status of inactive (dead) means MongoDB stopped — or never started. Jump to Step 2.

Step 2 — Start MongoDB

# Linux (systemd — Ubuntu, Debian, RHEL, CentOS)
sudo systemctl start mongod
sudo systemctl enable mongod   # auto-start on boot

# macOS (Homebrew)
brew services start mongodb-community

# macOS (manual, if installed without Homebrew)
mongod --config /usr/local/etc/mongod.conf

# Windows (Command Prompt as Administrator)
net start MongoDB

Step 3 — Verify the port is listening

Don't assume the start succeeded. Confirm MongoDB is actually accepting connections on port 27017:

# Linux / macOS
ss -tlnp | grep 27017
# or
lsof -i :27017

# Windows
netstat -ano | findstr 27017

You want to see output like this:

tcp  0  0  127.0.0.1:27017  0.0.0.0:*  LISTEN  1234/mongod

That line confirms MongoDB is listening. Try your app again — the ECONNREFUSED error should be gone.

Step 4 — If mongod fails to start, check the logs

Sometimes systemctl start mongod returns no error but the service immediately dies. The logs will tell you exactly what went wrong:

# Linux
sudo journalctl -u mongod -n 50 --no-pager

# Or check the log file directly
sudo tail -n 50 /var/log/mongodb/mongod.log

Common log errors and fixes

Permission denied on data directory

# Log output:
# exception in initAndListen: NonExistentPath: Data directory /var/lib/mongodb not found.

# Fix: create the directory and fix ownership
sudo mkdir -p /var/lib/mongodb
sudo chown -R mongodb:mongodb /var/lib/mongodb
sudo chmod 755 /var/lib/mongodb

Port already in use

# Log output:
# Address already in use for socket: 0.0.0.0:27017

# Find what's using the port
sudo lsof -i :27017

# Kill the process if it's a stale mongod
sudo kill -9 <PID>

Lock file from a previous crash

# Log output:
# Unclean shutdown detected. Please visit...

# Remove the lock file
sudo rm /var/lib/mongodb/mongod.lock
sudo mongod --repair --dbpath /var/lib/mongodb
sudo systemctl start mongod

Step 5 — Check the bind IP in mongod.conf

MongoDB running but still getting refused? The bind address is likely the problem. By default, MongoDB only listens on 127.0.0.1 — connections from other hosts or containers get rejected before they even reach the auth layer.

# Open the config file
sudo nano /etc/mongod.conf

# Look for this section:
net:
  port: 27017
  bindIp: 127.0.0.1   # ← Only accepts local connections

To allow connections from other hosts — a Docker container, a second server, etc. — change bindIp:

net:
  port: 27017
  bindIp: 0.0.0.0   # Accept from any IP (use with firewall rules)

Then restart:

sudo systemctl restart mongod

Security note: Only bind to 0.0.0.0 if MongoDB sits behind a firewall. Never expose port 27017 directly to the internet without authentication and network restrictions.

Step 6 — Firewall check

Connecting to a remote MongoDB host? A firewall could be silently dropping packets on port 27017. Open the port explicitly:

# Ubuntu (ufw)
sudo ufw allow 27017/tcp
sudo ufw status

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

Step 7 — Docker and Docker Compose

Docker adds a networking wrinkle. Inside a container, 127.0.0.1 points to the container itself — not the host machine. So if your Node.js app runs in Docker and MongoDB is on the host (or in a different container), the connection string needs to change:

# Wrong — resolves to the container's loopback, not the host
MONGODB_URI=mongodb://127.0.0.1:27017/mydb

# Correct — use host.docker.internal (Docker Desktop on macOS / Windows)
MONGODB_URI=mongodb://host.docker.internal:27017/mydb

# Correct — if MongoDB is a service in docker-compose.yml, use the service name
MONGODB_URI=mongodb://mongo:27017/mydb

Example docker-compose.yml:

services:
  app:
    build: .
    environment:
      - MONGODB_URI=mongodb://mongo:27017/mydb
    depends_on:
      - mongo
  mongo:
    image: mongo:7
    ports:
      - "27017:27017"

Verification

Use mongosh to confirm the connection works end-to-end:

mongosh mongodb://127.0.0.1:27017
# Expected:
# Connecting to: mongodb://127.0.0.1:27017/
# MongoServerVersion: 7.x.x
# >

Or test with a quick Node.js snippet using Mongoose:

const mongoose = require('mongoose');
mongoose.connect('mongodb://127.0.0.1:27017/test')
  .then(() => console.log('Connected!'))
  .catch(err => console.error(err));

Connected! in the output means the fix worked. No more ECONNREFUSED.