gRPC-based RPC Framework (Courier)

Dropbox developed Courier, a gRPC-based RPC framework, to standardize inter-service communication. Courier integrates gRPC with Dropbox's existing infrastructure for authentication, authorization, service discovery, stats, logging, and tracing. It provides features like service identity, TLS mutual authentication, ACLs, rate limiting, deadline propagation, and circuit-breaking to enhance security, observability, and reliability. The framework also includes introspection endpoints for debugging and performance optimizations like ECDSA keypairs for TLS handshakes.