What is the difference between application layer load balancers and network layer load balancers?

Layer 4 load balancers operate at the transport layer of the OSI model, distributing traffic based on IP addresses and ports. They do not analyze packet contents and are usually faster because they make decisions based on less information.

Layer 7 load balancers operate at the HTTP/HTTPS level and above. They can analyze request contents, such as URL, headers, cookies, and make routing decisions based on this data. This allows implementing more complex scenarios, such as content-based routing or authentication.

Example:

• Layer 4 balancer can direct traffic to servers on port 80 or 443.
• Layer 7 balancer can route requests with URL /api to one server, and requests with URL /static to another.