How Load Balancers Keep Websites Fast and Reliable

posted 5 min read

As we discussed Scaling in the last post today, I will try to explain the Load Balancer, so Let's get started

Imagine a scenario You have a bookstore that is getting incredibly popular day by day and as more people start to visit your bookstore you begin to face some issues like:

  • Overcrowding: Too many people in the store at once.
  • Long Checkout Lines: Some counters have very long lines, while others are not busy at all.
  • Customer Frustration: Long waits cause customers to leave without buying.
  • poor service: If one counter breaks down (the cashier is sick), the remaining counters become even more busy.

Now, How can you overcome these issues

Solving the Problem in a Physical Bookstore

we can use scaling approaches ,Let see how we can use Scaling :

a) Vertical Scaling (Make the Store Bigger)

  • Add More Counters in the existing store.
  • Hire more cashiers to handle the increasing load.
  • Create a Larger space to accommodate more customers.

Problem : When there are multiple counters, some customers still end up waiting in line at just one counter, while other counters stay empty. To solve this, we need a system that can evenly distribute customers across all counters, so no counter stays too busy or too idle.

b) Horizontal Scaling (Open More Branches)

  • Open multiple stores in different locations.
  • Customers visit the nearest store instead of overcrowding one.

Problem : If there’s no system guiding customers to the appropriate branch, some stores might be overrun, while others remain underutilized.

Enter the Load Balancer (Physical Context)

The Role of a Load Balancer:

In the physical bookstore, a staff member at the entrance acts as the load balancer:

  • They send customers to the least busy counter.
  • If a counter stops working (like if the cashier leaves), they guide customers to the counters that are still open.
  • This helps spread out the customers evenly, making wait times shorter and reducing frustration.

Example:

  • Counter 1 has 5 customers, Counter 2 has 2 customers, and Counter 3 is free.
  • The load balancer sends the next customer to Counter 3.

Now, let's see how this concept applies to an online bookstore with servers.

The Problem: Server Overload
For the online bookstore the website becomes extremely popular. The same problems occur, but in a digital form:

  • Overcrowding: When too many people try to use the website at the same time, the server gets slow or stops working.
  • Uneven Load Distribution: If there’s no system to share the work, one server may get all the traffic while others sit unused.
  • Unreliable Service: If one server fails, users can’t access the website.

To Overcome this issue online we can use load balancer

A load balancer is a tool that helps manage the flow of visitors to a website. It makes sure that the traffic is shared equally between different servers, so no single server gets too crowded.

Why is it used?

  • To balance traffic: It ensures that no server is overloaded with too many requests at once.
  • To keep the website running: If one server breaks, the load balancer sends the visitors to another working server.
  • To handle more visitors: It allows you to add more servers when needed, so the website can handle more users.

Pros of a Load Balancer:

  • Faster performance: It keeps the website fast by spreading the work across servers.
  • Keeps the website available: If one server goes down, the load balancer sends traffic to other servers, so the website stays online.
  • Helps in scaling: You can add more servers as your website grows, and the load balancer will distribute the traffic evenly.
  • Prevents server crashes: By not overloading any server, it prevents crashes.

Cons of a Load Balancer:

  • Risk of failure: If the load balancer itself fails, it can affect the whole system unless there's a backup.
  • Small delays: The load balancer may cause a small delay in sending the request to the right server.

Load Balancing Algorithms
In addition to helping distribute traffic, load balancers use specific algorithms to determine how the incoming requests are distributed to the different servers. Let’s explore the most commonly used load balancing algorithms:

  • Round Robin Algorithm

    This is the most basic and commonly used load balancing algorithm. It simply distributes requests to the servers one by one in a circular fashion, without considering the current load on the servers.

How it works:
Each incoming request is sent to the next server in line. Once the last server in the list is reached, the load balancer starts sending requests to the first server again.
Let me Explain you this by an Example:

  • Let’s say you have three servers: Server 1, Server 2, and Server 3.

    • Request 1 goes to Server 1.
    • Request 2 goes to Server 2.
    • Request 3 goes to Server 3.
    • Request 4 starts again and goes to Server 1.
  • Least Connections Algorithm

    the Least Connections algorithm considers how many active connections are already open on each server. The load balancer sends traffic to the server with the fewest active connections, ensuring that no server is overloaded.

  • How it works:
    The load balancer constantly monitors the number of active connections on each server. When a new request comes in, it sends the request to the server with the least number of active connections, helping to distribute the load evenly.
    Let me Explain you this by an Example:

  • Server 1 has 10 active connections.

  • Server 2 has 5 active connections.
  • Server 3 has 2 active connections.
    The load balancer will send the next request to Server 3, as it has the least number of active connections.

  • IP Hashing Algorithm

    The IP Hashing algorithm uses the client’s IP address to decide which server should handle their requests. This means a user with the same IP address will always connect to the same server. It’s helpful when a user’s session data (like login details or shopping cart) is stored on a specific server.
    How it Works:

  • The load balancer takes the user’s IP address (e.g., 192.168.1.10).

  • It runs the IP address through a formula (called "hashing") to pick a specific server.
  • Every time the user visits, the same IP will map to the same server.

Why Are These Algorithms Important?
These load balancing algorithms are crucial because they allow the load balancer to distribute traffic in the most efficient way possible, ensuring that:

  • Server Load is Balanced
  • Faster Response Times
  • Better Scalability

Choosing the Right Algorithm
The choice of load balancing algorithm largely depends on:

  • The traffic patterns: Predictable traffic is better suited for Round Robin, while unpredictable traffic may benefit more from Least Connections.
  • The type of service: Applications needing session consistency should use IP Hashing.

In conclusion, load balancers are essential for ensuring optimal performance and scalability in digital systems. Whether you're just learning or planning to implement one, understanding algorithms like Round Robin and Least Connections is crucial.

Do you Have a favorite algorithm or a question about implementation? Let’s keep the conversation going.

If you read this far, tweet to the author to show them you care. Tweet a Thanks
Great explanation, Riya!  The bookstore analogy really made load balancing easy to understand. I especially liked the breakdown of different algorithms like Round Robin and Least Connections. One question—how does a load balancer handle sudden traffic spikes in real-time? Does it automatically scale, or does it need manual intervention? Would love to hear your thoughts!
Great analogy! Very easy to understand. Well done

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