Load Balancer Configuration

Quick Start

Configure nginx to distribute traffic across multiple backend servers with health checks and automatic failover.

Instructions

Step 1: Define upstream block

Create an upstream block with your backend servers:

upstream backend { # Load balancing method (optional, defaults to round-robin) least_conn; # or ip_hash, or omit for round-robin

# Backend servers
server backend1.example.com:8080 weight=3;
server backend2.example.com:8080 weight=2;
server backend3.example.com:8080;

# Backup server (used when all primary servers are down)
server backup.example.com:8080 backup;

# Health check parameters
keepalive 32;

}

Step 2: Configure proxy in server block

Add proxy configuration to route traffic to the upstream:

server { listen 80; server_name example.com;

location / {
    proxy_pass http://backend;
    
    # Essential proxy 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;
    
    # Timeouts
    proxy_connect_timeout 60s;
    proxy_send_timeout 60s;
    proxy_read_timeout 60s;
    
    # Buffering
    proxy_buffering on;
    proxy_buffer_size 4k;
    proxy_buffers 8 4k;
}

}

Step 3: Add health checks

Configure passive health checks (active checks require nginx Plus):

upstream backend { server backend1.example.com:8080 max_fails=3 fail_timeout=30s; server backend2.example.com:8080 max_fails=3 fail_timeout=30s; server backend3.example.com:8080 max_fails=3 fail_timeout=30s; }

Parameters:

• max_fails : Number of failed attempts before marking server as unavailable

• fail_timeout : Time to wait before retrying a failed server

Step 4: Test and reload

Test configuration

nginx -t

Reload nginx

nginx -s reload

Load Balancing Methods

Round-robin (default): Distributes requests evenly across servers

upstream backend { server backend1.example.com:8080; server backend2.example.com:8080; }

Least connections: Routes to server with fewest active connections

upstream backend { least_conn; server backend1.example.com:8080; server backend2.example.com:8080; }

IP hash: Routes same client IP to same server (session persistence)

upstream backend { ip_hash; server backend1.example.com:8080; server backend2.example.com:8080; }

Weighted: Distributes based on server capacity

upstream backend { server backend1.example.com:8080 weight=3; # Gets 3x traffic server backend2.example.com:8080 weight=1; }

Common Patterns

WebSocket proxying

location /ws { proxy_pass http://backend; proxy_http_version 1.1; proxy_set_header Upgrade $http_upgrade; proxy_set_header Connection "upgrade"; }

Sticky sessions with cookie

upstream backend { server backend1.example.com:8080; server backend2.example.com:8080;

# Requires nginx Plus or third-party module
sticky cookie srv_id expires=1h domain=.example.com path=/;

}

Slow start (nginx Plus)

upstream backend { server backend1.example.com:8080 slow_start=30s; server backend2.example.com:8080 slow_start=30s; }

Advanced

For detailed information, see:

• Upstream Patterns - Advanced load balancing algorithms and patterns

• Health Checks - Comprehensive health check configuration

• Caching - Proxy caching strategies for load-balanced backends