How does a L4 load balancer differ from an L7 load balancer?

L4 and L7 load balancers differ in the OSI layer they operate at and, consequently, in their functionality.

• L4 (Transport Layer) — the load balancer operates at the TCP/UDP level. It distributes traffic based on IP addresses and ports without analyzing the packet contents. This is a faster and simpler method of load balancing but with less flexibility.

• L7 (Application Layer) — the load balancer operates at the HTTP/HTTPS level and above. It can analyze request contents, headers, URLs, cookies, and make routing decisions based on this data. It allows for complex rules, such as path-based routing, A/B testing, and authentication.

Example:

• An L4 load balancer can direct all TCP connections to one of the servers without protocol analysis.
• An L7 load balancer can route requests with /api to one backend, and requests with /static to another.

The choice depends on performance requirements and functionality.