Courier: Dropbox migration to gRPC

This post introduces Courier, Dropbox's gRPC-based RPC framework. It details the decision to adopt gRPC over legacy systems, highlighting its integration with existing infrastructure for security (service identity, TLS mutual auth, ACLs, rate limiting), observability (stats, tracing), and reliability (deadlines, circuit-breaking). Performance optimizations like ECDSA keypairs for TLS handshakes are also discussed.