Client-side vs Server-side Load Balancing (L4 vs L7).

1. Client-side vs Server-side LB:

• Server-side: Request hits a central LB (like Nginx), which then routes to an instance. (Pros: Simple. Cons: Central point of failure).
• Client-side: The calling service (Client) gets a list of instances from Service Discovery (Eureka) and decides which one to call. (Pros: Better performance, no central hop).

2. Layer 4 vs Layer 7:

• Layer 4 (Transport): Routes based on IP and Port. Very fast.
• Layer 7 (Application): Routes based on URL path, Headers, or Cookies. Slower but much more "Intelligent". Most microservices use L7 for routing.