What is the difference between an Application Load Balancer (ALB) and a Network Load Balancer (NLB)?
Options
- ALB works at layer 7 with path routing; NLB works at layer 4 for speed (Correct option)
- They are identical and only differ in the price of each hour
- ALB is meant for databases; NLB is meant for web traffic
- NLB understands URLs and paths; ALB does not understand them
Answer
ALB works at layer 7 (HTTP/HTTPS) with path/host routing; NLB works at layer 4 (TCP/UDP) for very high performance and static IPs
Why
Layers refer to the network model: layer 4 = transport (TCP/UDP ports), layer 7 = application (HTTP).
- ALB: understands HTTP, so it can route
/api/*to one service and/web/*to another, terminate TLS, and integrate with WAF. - NLB: forwards TCP/UDP connections without reading HTTP; ultra-low latency, millions of requests, fixed IPs.
Azure equivalents: Application Gateway (layer 7) and Azure Load Balancer (layer 4); Azure Front Door is a global layer 7.
Remember
ALB = L7 HTTP routing. NLB = L4 TCP speed.