Load Balancers & Proxies

• Load Balancer — Distributes incoming traffic across multiple servers
• Forward Proxy — Sits in front of clients (hides the client from the server)
• Reverse Proxy — Sits in front of servers (hides servers from the client)

flowchart TB
    subgraph Clients[Clients]
        U1[User 1]
        U2[User 2]
        U3[User 3]
    end

    subgraph LB[Load Balancer / Reverse Proxy]
        LBR[Distributes traffic<br/>Round-robin, least connections]
    end

    subgraph Servers[Backend Servers]
        S1[Server 1]
        S2[Server 2]
        S3[Server 3]
    end

    subgraph Database[Database]
        DB[(Database)]
    end

    U1 --> LBR
    U2 --> LBR
    U3 --> LBR
    LBR --> S1
    LBR --> S2
    LBR --> S3
    S1 --> DB
    S2 --> DB
    S3 --> DB

    style Clients fill:#3b82f6,color:#fff
    style LB fill:#7c3aed,color:#fff
    style Servers fill:#10b981,color:#fff
    style Database fill:#f59e0b,color:#fff

A load balancer distributes incoming requests across multiple servers so no single server gets overwhelmed.

Load balancing algorithms:

Round Robin       → Request 1 → Server A, Request 2 → Server B, Request 3 → Server C...
Least Connections → Send to server with fewest active connections
IP Hash           → Same user always goes to the same server (session persistence)
Weighted          → More powerful servers get more traffic

Why use a load balancer?

• Scalability — add more servers as traffic grows
• High availability — if one server fails, traffic goes to the others
• SSL termination — decrypt HTTPS at the load balancer (less work for servers)

A forward proxy sits between the client and the internet:

Client → Forward Proxy → Internet → Server

Used for:

• Anonymity — hides the client’s IP from the server
• Bypassing restrictions — access blocked websites
• Content filtering — schools/corporations block certain sites
• Caching — serve frequently accessed content faster

A reverse proxy sits between the internet and your servers:

Internet → Reverse Proxy → Server

Used for:

• Load balancing — distribute traffic
• Caching — cache responses to reduce server load
• SSL termination — handle HTTPS at the proxy
• Security — hide internal server details
• Rate limiting — prevent abuse

Common tools:

• A load balancer spreads traffic across multiple servers for scalability and reliability
• A forward proxy sits in front of clients (hides the user — like a VPN)
• A reverse proxy sits in front of servers (hides the server — like Cloudflare)
• Load balancers use algorithms like round-robin and least connections
• Common tools: Nginx (reverse proxy), HAProxy (load balancer), Cloudflare (CDN + proxy)