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intermediate
8 min read
System Design
10/14/2025
#load balancer #system design #scalability #high availability

Choosing the Right Load Balancer: A Practical Guide

Quick Summary (TL;DR)

A load balancer is a device or service that distributes incoming network traffic across multiple backend servers to ensure no single server becomes overwhelmed. This improves application responsiveness and reliability. The choice of load balancer depends on your needs: Layer 4 load balancers operate at the transport level (TCP/UDP) and are very fast, while Layer 7 load balancers operate at the application level (HTTP/HTTPS) and can make more intelligent, content-aware routing decisions.

Key Takeaways

  • Layer 4 for Speed, Layer 7 for Smarts: Use a Layer 4 load balancer when you need high performance and simple traffic distribution. Use a Layer 7 load balancer when you need to make routing decisions based on application-level information, such as URL paths, hostnames, or cookies.
  • Round Robin is a Simple Start: The Round Robin algorithm, which cycles through servers sequentially, is the simplest load balancing method. However, the Least Connections algorithm is often more effective as it directs traffic to the server with the fewest active connections.
  • Sticky Sessions are a Trade-off: “Sticky sessions” (or session affinity) direct all requests from a single user to the same backend server. This can be necessary for older, stateful applications but should be avoided in modern, stateless applications as it complicates scalability and failover.

The Solution

Load balancing is a fundamental component for building scalable and highly available systems. By placing a load balancer in front of your backend servers, you create a single point of entry for all client requests. The load balancer then intelligently distributes these requests across your pool of healthy servers. This not only prevents any one server from becoming a bottleneck but also allows you to seamlessly add or remove servers from the pool to handle fluctuating traffic loads. It also improves reliability by automatically redirecting traffic away from servers that have failed health checks.

Implementation Steps

  1. Determine Your Load Balancing Layer (4 vs. 7) If you just need to distribute TCP or UDP traffic and speed is paramount, choose a Layer 4 load balancer. If you are dealing with HTTP/HTTPS traffic and need to route based on paths (e.g., /api to API servers, /images to an image service), you need a Layer 7 load balancer.

  2. Select a Load Balancing Algorithm For most use cases, start with Round Robin for its simplicity or Least Connections for better traffic distribution. More advanced algorithms like Least Response Time can also be considered if server performance varies.

  3. Configure Health Checks The load balancer needs to know which servers are healthy enough to receive traffic. Configure a health check endpoint (e.g., a /health HTTP endpoint) on your backend servers. The load balancer will periodically poll this endpoint and stop sending traffic to any server that fails the check.

  4. Choose a Load Balancer Provider For most applications, a managed load balancer from a cloud provider (like AWS Elastic Load Balancer or Google Cloud Load Balancing) is the easiest and most reliable option. For on-premise or custom needs, software load balancers like NGINX or HAProxy are popular choices.

Common Questions

Q: What is the difference between a hardware and a software load balancer? A hardware load balancer is a dedicated physical appliance, offering very high performance but at a high cost and with less flexibility. A software load balancer is an application that runs on standard servers (e.g., NGINX, HAProxy), offering excellent flexibility and cost-effectiveness, which is why it’s the standard for most cloud-based applications.

Q: Can I use multiple load balancers? Yes, it’s common to use a combination. For example, you might use a Layer 4 load balancer for initial, high-volume traffic distribution across regions, and then use Layer 7 load balancers within each region to make more fine-grained routing decisions to specific services.

Q: How does a load balancer handle SSL/TLS? Layer 7 load balancers can perform SSL/TLS termination. This means the load balancer handles the decryption of incoming HTTPS traffic and sends unencrypted traffic to the backend servers. This offloads the computational overhead of SSL/TLS from your application servers and simplifies certificate management.

Tools & Resources

  • NGINX: A high-performance, open-source web server, reverse proxy, and load balancer. It is one of the most popular software load balancers in the world.
  • HAProxy: Another widely used, open-source software load balancer and reverse proxy that is known for its reliability and efficiency.
  • AWS Elastic Load Balancing (ELB): A managed load balancing service from Amazon Web Services that includes Application Load Balancers (Layer 7) and Network Load Balancers (Layer 4).

System Design & Architecture

Microservices & Security

DevOps & Infrastructure

Need Help With Implementation?

Setting up a resilient and scalable load balancing architecture is critical for modern applications. Built By Dakic provides cloud architecture and DevOps consulting to help you design and implement the right load balancing solution for your needs, ensuring high availability and performance. Get in touch for a free consultation.