What are the best practices for designing gRPC APIs at scale?

Designing gRPC APIs for large-scale production systems: (1) Schema registry — use Buf Schema Registry or Confluent Schema Registry to version and share .proto files across teams; prevent breaking changes with CI enforcement; (2) API versioning strategy — maintain parallel v1/v2 packages; use compatibility shims during migration; (3) Observability — instrument all services with OpenTelemetry; track RPC latency histograms, error rates by status code, and active stream count per service; (4) Deadlines — establish a deadline budget for each API tier (e.g., 100ms for latency-sensitive reads, 5s for mutations); enforce with interceptors; (5) Circuit breaking — configure Envoy or client-side circuit breakers to prevent cascade failures; (6) Graceful shutdown — drain in-flight streams before shutdown with a grace period; (7) Retries with idempotency — only retry idempotent operations; use request IDs to deduplicate; configure retry policies in service mesh rather than client code; (8) Rate limiting — implement per-client quotas via server-side interceptors using Redis sliding windows; (9) Documentation — treat .proto comments as API documentation; generate reference docs with protoc-gen-doc.