We are currently migrating our monolithic application to a microservices architecture on AWS. I'm trying to decide between a Network Load Balancer (Layer 4) and an Application Load Balancer (Layer 7). Since our API handles heavy JSON traffic and requires SSL termination, which option provides the best balance between low latency and advanced routing capabilities like path-based or host-based routing?
3 answers
For a microservices environment, a Layer 7 (ALB) is almost always the better choice because it operates at the application layer. This allows you to inspect the HTTP headers and route traffic to specific target groups based on the URL path, which is essential for microservices. While Layer 4 (NLB) offers lower latency by only looking at IP addresses and TCP ports, it lacks the "intelligence" to handle complex routing. If you need SSL termination at the edge to offload your backend servers, the ALB handles this natively, allowing your services to focus purely on processing business logic without the overhead of encryption.
How much of a latency spike can your application tolerate during the peak traffic hours when the load balancer is performing deep packet inspection?
Go with Layer 7 if you need path-based routing. It's much easier to manage one entry point that directs traffic to /auth, /users, and /orders microservices.
Barbara is spot on. We recently switched to path-based routing and it simplified our DNS management significantly since we no longer need a dozen subdomains for every single internal service.
James, that’s a valid concern. In most modern cloud environments, the latency added by an ALB for packet inspection is usually in the low milliseconds. Unless you are running high-frequency trading or real-time gaming, the benefits of smart routing and built-in WAF integration far outweigh the tiny performance hit. Most developers find the ALB's feature set indispensable for modern web apps.