Configuring Load Balancers

Prerequisites

Before using this skill, ensure:

• Backend servers are identified with IPs or DNS names
• Load balancer type is determined (ALB, NLB, Nginx, HAProxy)
• SSL certificates are available if using HTTPS
• Health check endpoints are defined
• Understanding of traffic distribution requirements (round-robin, least-connections)
• Cloud provider CLI installed (if using cloud load balancers)

Instructions

1. Select Load Balancer Type: Choose based on requirements (L4 vs L7, cloud vs on-prem)
2. Define Backend Pool: List backend servers with ports and weights
3. Configure Health Checks: Set check interval, timeout, and healthy threshold
4. Set Up SSL/TLS: Configure certificates and cipher suites
5. Define Routing Rules: Create path-based or host-based routing
6. Enable Session Persistence: Configure sticky sessions if needed
7. Add Monitoring: Set up logging and metrics collection
8. Test Configuration: Validate syntax and test traffic distribution

Output

Nginx Configuration:

# {baseDir}/nginx/load-balancer.conf
upstream backend_servers {
    least_conn;
    server 10.0.1.10:8080 weight=3;
    server 10.0.1.11:8080 weight=2;
    server 10.0.1.12:8080 backup;
}

server {
    listen 80;
    server_name app.example.com;

    location / {
        proxy_pass http://backend_servers;
        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_connect_timeout 5s;
        proxy_send_timeout 60s;
        proxy_read_timeout 60s;
    }

    location /health {
        access_log off;
        return 200 "healthy\n";
    }
}

AWS ALB (Terraform):

# {baseDir}/terraform/alb.tf
resource "aws_lb" "app_alb" {
  name               = "app-load-balancer"
  internal           = false
  load_balancer_type = "application"
  security_groups    = [aws_security_group.alb_sg.id]
  subnets            = aws_subnet.public[*].id
}

resource "aws_lb_target_group" "app_tg" {
  name     = "app-target-group"
  port     = 80
  protocol = "HTTP"
  vpc_id   = aws_vpc.main.id

  health_check {
    path                = "/health"
    interval            = 30
    timeout             = 5
    healthy_threshold   = 2
    unhealthy_threshold = 2
  }
}

resource "aws_lb_listener" "app_listener" {
  load_balancer_arn = aws_lb.app_alb.arn
  port              = "443"
  protocol          = "HTTPS"
  ssl_policy        = "ELBSecurityPolicy-TLS-1-2-2017-01"
  certificate_arn   = aws_acm_certificate.cert.arn

  default_action {
    type             = "forward"
    target_group_arn = aws_lb_target_group.app_tg.arn
  }
}

Error Handling

Backend Server Unreachable

• Error: "502 Bad Gateway" or connection refused
• Solution: Verify backend server IPs, ports, and firewall rules

SSL Certificate Error

• Error: "certificate verify failed"
• Solution: Check certificate validity, chain, and private key match

Health Check Failures

• Error: "Target is unhealthy"
• Solution: Verify health check path returns 200 status and backends are running

Configuration Syntax Error

• Error: "nginx: configuration file test failed"
• Solution: Run nginx -t to validate syntax and fix errors

Session Persistence Not Working

• Issue: Users losing session on subsequent requests
• Solution: Enable sticky sessions using cookie-based or IP-based persistence

Resources

• Nginx documentation: https://nginx.org/en/docs/
• HAProxy configuration guide: https://www.haproxy.org/
• AWS ALB documentation: https://docs.aws.amazon.com/elasticloadbalancing/
• GCP Load Balancing: https://cloud.google.com/load-balancing/docs
• Example configurations in {baseDir}/lb-examples/