Tools: Load Balancers Explained

The Scaling Problem ## What Is a Load Balancer? ## Why Use Load Balancers? ## Load Balancing Algorithms ## Layer 4 vs Layer 7 Load Balancing ## Health Checks ## Real-World Setup ## Load Balancer vs Reverse Proxy ## Key Takeaways When your application starts getting traffic, one server is never enough. At scale, distributing traffic correctly becomes one of the most important architectural decisions. In this article, we’ll break down: Even if the server is powerful, it will eventually hit limits: The solution is horizontal scaling. But how do users know which server to hit? That’s where load balancers come in. A load balancer is a system that: 1️⃣ Scalability Add more servers without changing client logic. 2️⃣ High Availability If one server fails, traffic is redirected. 3️⃣ Fault Tolerance Prevents cascading failures. 4️⃣ Zero-Downtime Deployments You can remove a server from rotation during updates. Round Robin Requests distributed sequentially. Simple, effective for uniform workloads. Least Connections Traffic goes to the server with the fewest active connections. Good for uneven workloads. IP Hash Same client IP → same backend server. Useful for session stickiness. Layer 4 (Transport Layer) Layer 7 (Application Layer) Load balancers constantly monitor backend servers. It is removed from rotation. This prevents sending traffic to unhealthy instances. In production systems, architecture often looks like this: Many tools (like NGINX) do both. Templates let you quickly answer FAQs or store snippets for re-use. Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink. Hide child comments as well For further actions, you may consider blocking this person and/or reporting abuse CODE_BLOCK: Clients → Load Balancer → Server Pool Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: Clients → Load Balancer → Server Pool CODE_BLOCK: Clients → Load Balancer → Server Pool CODE_BLOCK: Users ↓ Load Balancer ↓ Web Servers (Auto-scaled) ↓ Database / Cache Layer Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: Users ↓ Load Balancer ↓ Web Servers (Auto-scaled) ↓ Database / Cache Layer CODE_BLOCK: Users ↓ Load Balancer ↓ Web Servers (Auto-scaled) ↓ Database / Cache Layer - What a load balancer is - Why it’s needed - Types of load balancers - Algorithms used - Health checks - Real-world architecture patterns - 500,000 users - Peak traffic - CPU saturation - Memory exhaustion - Network bottlenecks - Accepts incoming client requests - Distributes them across multiple backend servers - Ensures no single server is overloaded - Works at TCP/UDP level - Doesn’t inspect HTTP content - Works at HTTP level - Can route based on: URL path Headers Cookies - Enables smarter routing - Stops responding - Returns errors - AWS ELB / ALB - Google Cloud Load Balancer - Sits in front of servers - Forwards requests - Specifically distributes load - Load balancers distribute traffic across servers - Enable horizontal scaling - Improve availability - Support multiple routing strategies - Critical in system design interviews