ALB vs NGINX vs HAProxy

AWS Application Load Balancer (ALB), NGINX, and HAProxy are the three most common load balancing solutions. ALB is a fully managed AWS service. NGINX and HAProxy are open-source, self-managed proxies that can run anywhere.

Architecture Overview

AWS ALB — Managed Service

ALB is a fully managed Layer 7 load balancer in AWS. It auto-scales, integrates with ACM for SSL, routes to ECS tasks, EKS pods, EC2 instances, and Lambda functions. You do not manage servers — AWS handles availability, scaling, and patching.

NGINX — Web Server + Reverse Proxy

NGINX is a high-performance web server and reverse proxy. It handles HTTP load balancing, SSL termination, caching, and request routing. NGINX Plus adds commercial features like active health checks, session persistence, and a real-time dashboard. OpenResty extends NGINX with Lua scripting.

HAProxy — Pure Load Balancer

HAProxy is purpose-built for load balancing and proxying. It consistently leads industry benchmarks for throughput and latency. Features include advanced ACLs, stick tables for session affinity, and agent-based health checks. HAProxy's stats page provides real-time metrics out of the box.

Performance Comparison

HAProxy and NGINX handle millions of concurrent connections with sub-millisecond added latency. ALB auto-scales but adds 1-5ms latency due to its managed architecture. For latency-critical system designs, self-managed proxies win.

At extreme scale, HAProxy's event-driven architecture can saturate 10Gbps+ links on commodity hardware. ALB's scaling is transparent but you cannot control or optimize it.

Cost Analysis

ALB charges per hour (~$16/month) plus per Load Balancer Capacity Unit (LCU). At high traffic volumes, ALB costs can exceed running dedicated NGINX or HAProxy instances on EC2.

NGINX and HAProxy are open source. Your cost is the compute they run on. For cost-aware architectures, self-managed load balancers on reserved instances are often cheaper.

System Design Interviews

In system design interviews, load balancer choice signals architecture maturity. ALB for managed simplicity, NGINX for web-serving + proxying, HAProxy for raw performance. Many production architectures use ALB in front of NGINX/HAProxy for defense in depth.

See also: load balancing concepts and infrastructure patterns.