To ensure high availability and performance of Web applications, it is now common to use a load-balancer.
While some people uses layer 4 load-balancers, it can be sometime recommended to use layer 7 load-balancers to be more efficient with HTTP protocol.
NOTE: To understand better the difference between such load-balancers, please read the Load-Balancing FAQ.
A load-balancer in an infrastructure
The picture below shows how we usually install a load-balancer in an infrastructure:
This is a logical diagram. When working at layer 7 (aka Application layer), the load-balancer acts as a reverse proxy.
So, from a physical point of view, it can be plugged anywhere in the architecture:
- in a DMZ
- in the server LAN
- as front of the servers, acting as the default gateway
- far away in an other separated datacenter