When I first encountered network diagrams showing load balancers positioned behind firewalls, my immediate reaction was skepticism. After all, this architecture means:

• All inbound traffic must first traverse the firewall
• The firewall becomes a potential bottleneck
• Single point of failure concerns emerge

Here's a simple visualization of the traffic flow:

Internet -> Firewall -> Load Balancer -> Web Servers

The primary rationale becomes clear when we examine modern security requirements. Firewalls provide:

• Deep packet inspection
• Protocol validation
• Stateful connection tracking

Consider this Nginx configuration snippet that would sit behind such an architecture:

server {
    listen 80;
    server_name example.com;
    
    # Only accept connections from firewall IP
    allow 192.168.1.1;
    deny all;
    
    location / {
        proxy_pass http://backend_pool;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    }
}

While it's true that this adds latency, modern firewalls handle significant throughput. The tradeoff becomes:

Major cloud providers follow this pattern. AWS's documentation explicitly states:

"Application Load Balancers should be placed in public subnets, protected by network ACLs and security groups acting as firewalls."

Here's a Terraform example for such a setup:

resource "aws_security_group" "alb_firewall" {
  name        = "alb_firewall"
  description = "Allow HTTP/HTTPS to ALB"
  
  ingress {
    from_port   = 80
    to_port     = 80
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

resource "aws_lb" "web" {
  name               = "web-alb"
  internal           = false
  load_balancer_type = "application"
  security_groups    = [aws_security_group.alb_firewall.id]
  subnets            = aws_subnet.public.*.id
}

The firewall-LB combination enables sophisticated protection:

# Example WAF rule that complements firewall protection
SecRule REQUEST_HEADERS:User-Agent "@pm scanner crawler" \
    "id:1001,phase:1,deny,msg:'Bad Bot Detected'"

This layered approach creates defense in depth where the firewall handles network-level threats while the load balancer manages application-layer concerns.

When implementing an F5 BIG-IP load balancer in a web server infrastructure, the placement decision between firewall and load balancer creates distinct traffic patterns. Let's examine the packet flow in both scenarios:

# Typical packet flow in firewall-behind-LB configuration:
Internet → F5 LB (VIP) → Internal Web Servers

# Packet flow in firewall-forward configuration:
Internet → Firewall → F5 LB (VIP) → Internal Web Servers

The primary rationale for placing the firewall first stems from defense-in-depth principles. Modern web applications face sophisticated attacks that require multiple security layers:

• Firewalls filter L3/L4 attacks before they reach the LB
• Web Application Firewalls (WAF) handle L7 protections
• LB maintains session persistence and health monitoring

While firewall placement does introduce potential bottlenecks, modern hardware mitigates these concerns:

// Sample throughput metrics (hypothetical):
Firewall-forward: 12Gbps throughput with 50μs latency  
LB-forward: 15Gbps throughput with 35μs latency

The 20% throughput difference often becomes negligible when considering security benefits.

The single point of failure concern can be addressed through proper HA design:

# Example HA firewall configuration (Cisco ASA):
failover lan unit primary
failover lan interface failover GigabitEthernet0/3
failover key *****
failover link failover GigabitEthernet0/3

Major cloud providers demonstrate hybrid approaches that combine both models:

• AWS: Internet-facing ALB with security groups
• Azure: Application Gateway behind Network Security Groups
• GCP: Global Load Balancer with Cloud Armor WAF

For enterprises with F5 deployments, consider these best practices:

# F5 iRule example for additional security
when HTTP_REQUEST {
    if { [HTTP::header User-Agent] contains "malicious-bot" } {
        drop
    }
    pool web_pool
}

The optimal architecture depends on your specific threat model, performance requirements, and existing infrastructure.