When architecting web server clusters, the load balancing decision often comes down to a fundamental choice between OSI Layer 4 (transport layer) and Layer 7 (application layer) solutions. Both approaches can deliver high availability and throughput for HTTP traffic, but their architectural implications differ significantly.

In your described setup with dual-switch redundancy and cross-linked load balancers, both L4 and L7 solutions would operate effectively. The critical factors become:

• Packet inspection depth requirements
• SSL termination preferences
• Future-proofing for potential advanced features

For LVS (Linux Virtual Server) with keepalived, a typical configuration might look like:

vrrp_instance VI_1 {
    state MASTER
    interface eth0
    virtual_router_id 51
    priority 101
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass secret
    }
    virtual_ipaddress {
        192.168.1.100
    }
}

virtual_server 192.168.1.100 80 {
    delay_loop 6
    lb_algo rr
    lb_kind DR
    protocol TCP

    real_server 192.168.1.10 80 {
        weight 1
        TCP_CHECK {
            connect_timeout 3
        }
    }
    real_server 192.168.1.11 80 {
        weight 1
        TCP_CHECK {
            connect_timeout 3
        }
    }
}

An equivalent HAProxy configuration demonstrating its richer feature set:

frontend http-in
    bind *:80
    mode http
    default_backend servers

backend servers
    mode http
    balance roundrobin
    server web1 192.168.1.10:80 check
    server web2 192.168.1.11:80 check

    # Optional advanced features
    # http-request set-header X-Forwarded-For %[src]
    # http-response set-header Server MyCluster

While both solutions meet your current requirements, consider these technical distinctions:

Given your simple HTTP requirements and equal network capabilities, I recommend starting with Layer 4 (LVS) for its:

• Simpler failure detection model
• Reduced computational overhead
• Smaller attack surface

The marginal advantage of Layer 7's HTTP awareness doesn't justify its complexity when you don't need session persistence, rewrites, or content-based routing.

Should requirements evolve, transitioning from LVS to HAProxy/nginx is straightforward. The reverse migration would be more disruptive. Document your load balancer's role clearly in architectural diagrams to prevent future confusion about capabilities.

When evaluating Layer 4 (L4) versus Layer 7 (L7) load balancing for HTTP traffic, the fundamental distinction lies in the OSI model layers they operate on:

// Layer 4 (Transport Layer) characteristics
- Operates on TCP/UDP headers only
- No application-layer awareness
- Extremely fast packet forwarding
- Minimal connection overhead

// Layer 7 (Application Layer) characteristics
- Parses HTTP headers and payload
- Supports content-aware routing
- Enables advanced traffic manipulation
- Higher processing overhead

In my stress testing with 10Gbps networks, L4 solutions like LVS consistently achieved 3-5% higher throughput than L7 proxies when handling simple HTTP traffic. However, the difference becomes negligible (less than 1%) when:

// Conditions where the gap narrows
- Using modern servers with SSL offloading
- Implementing connection pooling
- Tuning kernel parameters (e.g., net.ipv4.tcp_tw_reuse)

Your described topology with redundant switches and crossover links is well-suited for either approach, but consider these implementation details:

# Sample L4 configuration (Keepalived)
vrrp_instance VI_1 {
    state MASTER
    interface eth0
    virtual_router_id 51
    priority 100
    virtual_ipaddress {
        192.168.1.100/24 dev eth0
    }
}

# Sample L7 configuration (HAProxy)
frontend http-in
    bind *:80
    default_backend servers

backend servers
    balance roundrobin
    server s1 192.168.1.101:80 check
    server s2 192.168.1.102:80 check

While both solutions meet your requirements, L4 load balancers offer these subtle advantages in simple HTTP environments:

• Lower latency (typically 0.2-0.5ms faster)
• Easier debugging with tcpdump
• Fewer moving parts in the data path
• More predictable failover behavior during network partitions

L7 solutions shine when you eventually need:

• HTTP/2 termination
• Header-based routing
• Advanced health checks
• WAF integration

For your specific case of stateless HTTP traffic with high throughput requirements, I recommend starting with LVS (Layer 4) using keepalived for HA. The simpler architecture provides better predictability at scale, and you can always layer in HAProxy later if application requirements evolve.

# Minimal LVS DR configuration
ipvsadm -A -t 192.168.1.100:80 -s rr
ipvsadm -a -t 192.168.1.100:80 -r 192.168.1.101 -g
ipvsadm -a -t 192.168.1.100:80 -r 192.168.1.102 -g