API Design, Contract Engineering & Service Protocols

Distributed services live or die by their communication contracts. An inefficient serialization format wastes gigabytes of network bandwidth and thousands of CPU cycles parsing strings. A careless schema modification can instantly crash downstream consumers in production.

This module deconstructs modern service communication and contract engineering:

• Wire Protocols: HTTP/1.1 vs. HTTP/2 and HTTP/3 multiplexing, binary framing, header compression (HPACK/QPACK), and connection pooling.
• Protocol Buffers & Schema Evolution: How tag-based encoding achieves dense binary payloads and enables backward and forward compatibility without distributed lockstep deployments.
• API Ergonomics & Pagination: Why naive OFFSET pagination causes $O(N)$ database scans and phantom duplicates, and how keyset/cursor pagination guarantees deterministic $O(1)$ seek performance.
• Resilience Semantics: Idempotency keys, distributed deadline propagation, and cancellation trees that terminate unneeded downstream RPCs when user requests are cancelled.