The moment computation crosses a process boundary over an asynchronous packet network, two fundamental illusions of single-machine programming collapse: partial failure (a remote node or link can fail independently leaving the caller in an ambiguous UNKNOWN state) and the absence of a global physical clock (separate servers possess independent quartz oscillators that drift apart between NTP syncs).
Every distributed protocol in the remainder of this curriculum—from gRPC deadlines, transactional outbox relays, and stream watermarks to Raft consensus, Dynamo quorums, and Google Spanner’s TrueTime—exists to overcome these two realities. This chapter establishes the foundational mechanics of partial failure, idempotent retry safety, physical clock skew bounds, Lamport logical timestamps, and Vector Clocks.