Building Enterprise JavaScript Applications

Layer 4/7 load balancers

Another way to load balance client requests is to use a load balancer. Instead of exposing the backend servers on multiple IP addresses and letting the client pick which server to use, we can instead keep our backend servers hidden behind a private local network. When a client wants to reach our application, it would send the request to the load balancer, which will forward the requests to the backends.

Generally speaking, there are two types of load balancers—Layer 4 (L4), Layer 7 (L7). Their names relate to the corresponding layer inside the Open Systems Interconnection (OSI) reference model—a standard conceptual model that partitions a communication system into abstraction layers:

There are numerous standard protocols ...