• Protocols (HTTP/1, HTTP/2, gRPC, databases, caching, etc.). • Infrastructures (IaaS, CaaS, on premise, etc.). • Intermediate load balancers (AWS ELB, F5, etc.). • Observability output (stats, tracing, and logging). • Implementations (often partial) of retry, circuit breaking, rate limiting, timeouts, and other distributed systems best practices. • Authentication and Authorization. • Per language libraries for service calls.