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Load Balancers

Distributing traffic evenly across backend fleets

A Load Balancer (LB) acts as a traffic cop sitting in front of your web servers. It intercepts all incoming HTTP/HTTPS queries and distributes them across a fleet of backend servers.

Why do we need it?

  • High Availability: If one server crashes, the load balancer routes traffic to the surviving servers seamlessly.
  • Scalability: By adding more servers behind the load balancer, your application can handle millions of requests without changing client configurations.
  • Resource Optimization: Prevents any single server from becoming a bottleneck by spreading the CPU/Memory load.

    • In this scenario, we have a Client sending parallel requests, a Load Balancer, and 3 Web Servers.

    Load balancers decide where to route traffic using specific algorithms:

  • Round Robin: Routes requests sequentially (Server 1 ➔ Server 2 ➔ Server 3 ➔ Server 1). It assumes all servers have equal capacity.
  • Random: Dispatches requests completely at random. Useful for testing or when request load is extremely light.
  • IP Hash: Computes a hash of the client's IP address (e.g. 192.168.1.50) and maps it to a specific server. This ensures the same client *always* lands on the same server, preserving session/cache persistence.

    • Interactive Checkpoints

    Click on the check-points below to configure the simulator instantly and see them in action!

    Visualize Round Robin Routing

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    Click here to set the Load Balancer to 'Round Robin' and run the simulation. Watch how each request goes sequentially to Server 1, 2, and 3.

    Enforce IP Hash Stickiness

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    Click here to set the strategy to 'IP Hash'. Run the simulation to see how a client's requests stick to a single server based on their IP hash value.

    In the real world, servers crash or undergo updates. A load balancer uses health checks to detect dead nodes. If a server is unhealthy (or has zero capacity), the load balancer skips it and routes requests to active servers.

    Try it Yourself:

    1. Select Server 1 in the graph canvas.

    2. Under ⚙️ Configure Node, set its Connections Capacity to 0.

    3. Press Play or click Reset & Play to run.

    4. Observe how the load balancer skips Server 1 entirely and balances traffic only between Server 2 and Server 3!

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