SayONS

SayONS, short for Say-Once Notification System, is a protocol and reference implementation designed to provide reliable, exactly-once delivery semantics for event notifications in distributed systems. It aims to prevent duplicate processing and ensure traceable delivery across heterogeneous components, including microservices, IoT gateways, and data pipelines.

Origin and development: The concept emerged from research on decoupled architectures in the early 2020s. The SayONS specification was formalized by a collaborative team at the Institute for Distributed Computation, with open-source reference implementations published by community maintainers and corporate sponsors.

Key concepts: SayONS relies on unique message identifiers, cryptographic signing, and per-processor idempotency keys. A verification layer records processed IDs to prevent replay. The protocol defines message formats, delivery workflows, and protections against replay attacks, and can operate over HTTP, MQTT, gRPC, and other transports in both push and pull models.

Architecture and lifecycle: Producers create signed notifications which are routed through brokers to verifiers or consumers. A reconciliation service maintains a durable store of processed message IDs and state to enable exactly-once processing. Reliability modes include at-most-once, at-least-once, and exactly-once, each with associated latency and throughput implications.

Applications and limitations: SayONS is proposed for supply chain eventing, healthcare updates, financial transactions, and other domains where deduplication and auditability matter. Adoption requires widespread component support and careful key management; performance overhead and operational complexity are potential drawbacks.

See also: exactly-once semantics; idempotence; replay protection; distributed messaging. Notable implementations include several open-source projects and vendor-specific adapters that explore SayONS compatibility with existing messaging brokers.