What load balancers are you familiar with? What experience do you have working with them and what technologies have you used?

The following types of load balancers are known:

• Hardware Load Balancers: Specialized devices. Example: F5 BIG-IP.
• Software Load Balancers: Operate as software. Examples: HAProxy, Nginx, AWS Elastic Load Balancing (ELB), Google Cloud Load Balancing, Azure Load Balancer.

Experience includes working with HAProxy and Nginx as software load balancers, as well as with cloud solutions like AWS ELB (Application Load Balancer and Network Load Balancer).

HAProxy:

• Used for balancing TCP and HTTP traffic.
• Configurations were made through configuration files.
• Used for:
  • Distributing HTTP requests among web servers.
  • Ensuring high availability of databases (TCP traffic).
• Implemented:
  • Load balancing algorithms (round-robin, leastconn).
  • Server health checks.
  • SSL termination.

# Example HAProxy configuration
global
    log /dev/log    local0
    chroot /var/lib/haproxy
    stats socket /run/haproxy/admin.sock mode 660 level admin expose-fd listeners
    stats timeout 30s
    user haproxy
    group haproxy
    daemon

defaults
    log     global
    mode    http # or tcp
    option  httplog
    option  dontlognull
    timeout connect 5000ms
    timeout client  50000ms
    timeout server  50000ms
    errorfile 400 /etc/haproxy/errors/400.http
    errorfile 403 /etc/haproxy/errors/403.http
    errorfile 408 /etc/haproxy/errors/408.http
    errorfile 500 /etc/haproxy/errors/500.http
    errorfile 502 /etc/haproxy/errors/502.http
    errorfile 503 /etc/haproxy/errors/503.http
    errorfile 504 /etc/haproxy/errors/504.http

frontend http_front
    bind *:80
    default_backend http_back

backend http_back
    balance roundrobin # Load balancing algorithm
    server s1 192.168.1.10:80 check # Server 1 with health check
    server s2 192.168.1.11:80 check # Server 2 with health check

Nginx:

• Used as reverse proxy and HTTP(S) traffic load balancer.
• Configurations were made in nginx.conf or included files.
• Used for:
  • Distributing load among web servers and microservices.
  • Caching, compression, SSL termination.
• Implemented:
  • Various load balancing methods (round-robin, least_conn, ip_hash).
  • Server health checks in the commercial version (Nginx Plus) or with modules.
  • Virtual host configurations.

# Example Nginx configuration
http {
    upstream backend_servers {
        server 192.168.1.20:8080 weight=1; # Server 1 with weight
        server 192.168.1.21:8080 weight=1; # Server 2 with weight
        # least_conn; # Another load balancing method
    }

    server {
        listen 80;
        server_name example.com;

        location / {
            proxy_pass http://backend_servers; # Proxy to server group
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
            # Other proxy settings
        }
    }
}

AWS ELB:

• Application Load Balancer (ALB): Used for balancing HTTP/HTTPS traffic. Layer 7.
  • Routing requests based on URL, headers, and HTTP methods.
  • Integration with Auto Scaling Groups.
  • SSL termination, Web Application Firewall (WAF).
• Network Load Balancer (NLB): Used for balancing TCP/UDP traffic at Layer 4.
  • High performance and low latency.
  • Used for balancing traffic to databases, game servers, and other latency-sensitive applications.

Experience included configuring Listeners, Target Groups, health checks, and integrating with other AWS services via AWS Management Console, AWS CLI, and Terraform.

Technologies:

• Configuration: Manual editing of files, Ansible, Chef, Puppet.
• Infrastructure-as-code: Terraform for automated deployment and management of load balancers in the cloud.
• Monitoring: Prometheus, Grafana with exporters for HAProxy/Nginx or via CloudWatch for AWS ELB.
• CI/CD: Including configuration and reconfiguration of load balancers in CI/CD pipelines.

Overall, the choice of load balancer depended on application requirements (traffic type, performance, functionality), infrastructure (cloud or on-premise), and budget.