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Load Balancer in System Design

My next post in System Design series! In this post, we will explore the concept of Load Balancers. Load balancing is a crucial component in building scalable and reliable systems, ensuring that your application can handle varying loads efficiently and continue to provide a smooth user experience.

What is a Load Balancer?

A Load Balancer is a device or software that distributes incoming network traffic across multiple servers. The goal is to ensure that no single server becomes overwhelmed, thus improving the performance and reliability of the application.

Real-World Example:

Imagine our bookstore experiencing a surge of customers during a holiday sale. If only one cashier is available, the line will grow long, and customers will become frustrated. To handle the increased load, we could add more cashiers and distribute customers evenly among them. This way, no single cashier is overwhelmed, and customers are served more efficiently.

Fig: Balancing customers at a bookstore

How it Relates to Web Applications:

In a web application, a load balancer distributes incoming requests across multiple servers. This ensures that no single server handles too many requests, which could slow down the application or cause it to crash. By distributing the load, the application remains responsive and reliable.

Fig: A load balancer helps navigate new traffic

Types of Load Balancers

  1. Hardware Load Balancers:
    • Definition: Physical devices dedicated to load balancing tasks.
    • Pros: High performance, dedicated resources, and robust security features.
    • Cons: Expensive, requires physical space, and can be complex to manage.
  2. Software Load Balancers:
    • Definition: Software solutions that perform load balancing tasks.
    • Pros: Cost-effective, flexible, and easy to deploy.
    • Cons: Can be limited by the hardware they run on, may require more management.
  3. Cloud Load Balancers:
    • Definition: Load balancing services provided by cloud platforms.
    • Pros: Scalable, managed by cloud providers, and integrates well with cloud services.
    • Cons: Dependent on the cloud provider, can incur additional costs.

Load Balancing Algorithms

Load balancers use various algorithms to decide how to distribute incoming traffic:

  1. Round Robin:
    • Definition: Distributes requests sequentially across servers.
    • Pros: Simple and effective for equally powerful servers.
    • Cons: Does not account for server load or capacity.
  2. Least Connections:
    • Definition: Directs traffic to the server with the fewest active connections.
    • Pros: Balances load more efficiently, especially with varying server capacities.
    • Cons: Can lead to uneven distribution if not managed properly.
  3. IP Hash:
    • Definition: Distributes requests based on the client’s IP address.
    • Pros: Ensures that requests from the same client go to the same server.
    • Cons: Can cause uneven load distribution if client requests are not evenly distributed.

Example: Load Balancer in Action

Imagine your web application is experiencing a surge in traffic due to a successful marketing campaign.

  1. Without Load Balancer:
    • All requests go to a single server.
    • The server becomes overwhelmed and starts responding slowly or crashes.
    • Users experience delays or errors.
  2. With Load Balancer:
    • Requests are distributed across multiple servers.
    • Each server handles a manageable amount of traffic.
    • The application remains responsive, and users have a smooth experience.

Comparison Table:

AspectBookstore ExampleWeb Application Example
Without Load BalancerOne cashier handles all customersOne server handles all requests
With Load BalancerMultiple cashiers with managed queuesMultiple servers with distributed requests
Pros of Load BalancerFaster service, no overwhelmed cashierImproved performance, reliability, and scalability
Cons of Load BalancerRequires coordination among cashiersRequires setup and management

Importance of Load Balancers

Challenges

Video Explanation:

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