Nginx Load Balancing

You are a system administrator or DevOps engineer. The user wants to configure Nginx as a load balancer with active health checks across multiple backend servers.

What to check first

• Run nginx -v to confirm Nginx is installed (version 1.9.0+ required for active health checks)
• Verify backend servers are accessible: curl http://backend1:8080/health && curl http://backend2:8080/health
• Check current Nginx configuration location with nginx -T and locate the main config file (usually /etc/nginx/nginx.conf)

Steps

1. Open /etc/nginx/nginx.conf or create a new upstream config file in /etc/nginx/conf.d/upstream.conf
2. Define an upstream block with multiple backend servers and assign weights to distribute traffic proportionally
3. Add the health_uri parameter to each upstream server to specify which endpoint Nginx will check
4. Configure health check intervals with health_interval (milliseconds) and health_timeout (how long to wait for response)
5. Set health_type to http and specify health_http_version as HTTP/1.1 for proper health check requests
6. In your server block, reference the upstream with proxy_pass http://upstream_name; to route traffic
7. Add proxy_set_header Host $host; and proxy_set_header X-Real-IP $remote_addr; to preserve client info
8. Test the configuration with nginx -t and reload with systemctl reload nginx or nginx -s reload

Code

# /etc/nginx/conf.d/load_balancer.conf

upstream backend_servers {
    least_conn;
    
    server backend1.local:8080 weight=5 max_fails=3 fail_timeout=30s;
    server backend2.local:8080 weight=3 max_fails=3 fail_timeout=30s;
    server backend3.local:8080 weight=2 max_fails=3 fail_timeout=30s;
    
    # Active health checks (Nginx Plus feature, requires commercial license)
    # For open-source Nginx, use passive health checks with max_fails/fail_timeout
    
    keepalive 32;
}

server {
    listen 80;
    server_name example.com;

    location / {
        proxy_pass http://backend_servers;
        proxy_http_version 1.1;
        
        # Preserve original request headers
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_set_header Connection "";
        
        # Timeouts
        proxy_connect_timeout 5s;
        proxy_send_

Note: this example was truncated in the source. See the GitHub repo for the latest full version.

Common Pitfalls

• Treating this skill as a one-shot solution — most workflows need iteration and verification
• Skipping the verification steps — you don't know it worked until you measure
• Applying this skill without understanding the underlying problem — read the related docs first

When NOT to Use This Skill

• When a simpler manual approach would take less than 10 minutes
• On critical production systems without testing in staging first
• When you don't have permission or authorization to make these changes

How to Verify It Worked

• Run the verification steps documented above
• Compare the output against your expected baseline
• Check logs for any warnings or errors — silent failures are the worst kind

Production Considerations

• Test in staging before deploying to production
• Have a rollback plan — every change should be reversible
• Monitor the affected systems for at least 24 hours after the change