Load Balancing Strategies Cheat Sheet
Covers core load balancing algorithms, Layer 4 vs Layer 7 balancing, health checks, and configuration examples using NGINX and AWS ELB.
2 PagesIntermediateJan 28, 2026
Load Balancing Algorithms
Common algorithms used to distribute traffic across backend servers.
- Round Robin- Requests distributed sequentially across all servers in order
- Weighted Round Robin- Servers with higher weight receive proportionally more requests
- Least Connections- Routes to the server with the fewest active connections
- Weighted Least Connections- Combines connection count with a server capacity weight
- IP Hash- Hashes client IP to consistently route the same client to the same server
- Least Response Time- Routes based on lowest latency plus fewest active connections
- Random- Picks a server at random, often combined with 'power of two choices'
Layer 4 vs Layer 7
Key differences between transport-layer and application-layer load balancing.
- Layer 4 (Transport)- Routes based on IP/port using TCP/UDP, no payload inspection, very fast
- Layer 7 (Application)- Routes based on HTTP headers, URL path, cookies; enables content-based routing
- AWS NLB- Layer 4 load balancer, handles millions of requests/sec with static IPs
- AWS ALB- Layer 7 load balancer, supports path/host-based routing and WebSockets
- SSL Termination- L7 LBs can decrypt TLS at the balancer, offloading CPU work from backends
NGINX Load Balancer Config
Basic upstream block for round-robin and weighted balancing.
nginx
upstream backend { least_conn; # use least connections algorithm server 10.0.0.1:8080 weight=3; server 10.0.0.2:8080 weight=1; server 10.0.0.3:8080 backup; # only used if others are down}server { listen 80; location / { proxy_pass http://backend; proxy_set_header Host $host; proxy_set_header X-Real-IP $remote_addr; }}
Health Check Configuration
Defining active health checks so unhealthy targets are removed automatically.
bash
# AWS CLI: configure ALB target group health checkaws elbv2 modify-target-group \ --target-group-arn arn:aws:elasticloadbalancing:...:targetgroup/my-tg \ --health-check-protocol HTTP \ --health-check-path /healthz \ --health-check-interval-seconds 15 \ --healthy-threshold-count 2 \ --unhealthy-threshold-count 3
Pro Tip
Set your health check interval and timeout tighter than your deployment rollout speed, otherwise the LB will keep sending traffic to instances mid-restart during a rolling deploy.
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