API gateway
What an API gateway does, how Spring Cloud Gateway routes, filters and rate-limits requests, and when to use a gateway versus a BFF.
Service discovery
How services find each other with Eureka, Consul or Kubernetes DNS, client-side versus server-side discovery, health checks and load balancing.
Config server
How Spring Cloud Config Server serves configuration from Git, refreshes it at runtime, encrypts secrets, and when Kubernetes ConfigMaps are a better choice.