Nginx Load Balancing Updates Adding and Removing Backend Instances

Nginx Load Balancing Updates

As your traffic grows, you need to add more Node.js instances. This guide covers updating Nginx for load balancing.

Initial Load Balancing Config

upstream nodejs_backend {
    server 127.0.0.1:3000;
}

Adding More Instances

upstream nodejs_backend {
    server 127.0.0.1:3000;
    server 127.0.0.1:3001;
    server 127.0.0.1:3002;
}

# Start new instances
PORT=3001 pm2 start src/server.js --name api-2
PORT=3002 pm2 start src/server.js --name api-3

# Update Nginx
sudo nginx -t && sudo systemctl reload nginx

Load Balancing Methods

# Round-robin (default)
upstream backend {
    server 127.0.0.1:3000;
    server 127.0.0.1:3001;
}

# Least connections
upstream backend {
    least_conn;
    server 127.0.0.1:3000;
    server 127.0.0.1:3001;
}

# IP hash (for WebSockets/sessions)
upstream backend {
    ip_hash;
    server 127.0.0.1:3000;
    server 127.0.0.1:3001;
}

# Weighted (for different capacity servers)
upstream backend {
    server 127.0.0.1:3000 weight=3;
    server 127.0.0.1:3001 weight=1;
}

Health Checks

upstream backend {
    server 127.0.0.1:3000 max_fails=3 fail_timeout=30s;
    server 127.0.0.1:3001 max_fails=3 fail_timeout=30s;
}

Removing an Instance (Zero Downtime)

# Mark as down (Nginx stops sending new requests)
upstream backend {
    server 127.0.0.1:3000;
    server 127.0.0.1:3001 down;  # Temporarily down
}

# Reload Nginx
sudo systemctl reload nginx

# Stop the instance
pm2 stop api-2

# Remove from config when done
sudo nano /etc/nginx/sites-available/devtinder
# Remove the 'down' line
sudo systemctl reload nginx

The Takeaway

To update Nginx load balancing: add new servers to the upstream block, choose a method (round-robin, least_conn, ip_hash, weighted), set health checks (max_fails, fail_timeout), use 'down' to remove instances with zero downtime, and reload after each change. For WebSockets, always use ip_hash for sticky sessions.