Lesson 1: Load Balancers#

What is a Load Balancer?#

A load balancer sits between clients and servers, distributing incoming network traffic across a group of backend servers. This ensures that no single server bears too much load.

Types of Load Balancing#

Layer 4 (Transport Layer)#

• Decisions based on IP address and TCP/UDP ports.
• Faster, less CPU intensive.
• Does not inspect the content of the request.

Layer 7 (Application Layer)#

• Decisions based on the content of the message (URL, HTTP headers, cookies).
• Can route traffic to different services based on URL (e.g., /images to image servers).
• More CPU intensive but smarter.

Algorithms#

• Round Robin: Requests are distributed sequentially.
• Least Connections: Sends request to the server with the fewest active connections.
• IP Hash: The client’s IP address is used to determine which server receives the request (useful for session stickiness).

🛠️ Sruja Perspective: Modeling Load Balancers#

In Sruja, a load balancer is typically modeled as a container or component that sits in front of your application servers.

architecture "Web Application" {
    container LB "Nginx Load Balancer" {
        technology "Nginx"
        tags "load-balancer"
        description "Layer 7 load balancer routing traffic based on URL paths."
    }

    container AppServer "App Server" {
        technology "Python, Django"
        tags "scaled"
    }

    // Traffic flow
    LB -> AppServer "Distributes requests (Round Robin)"
}