Show HN: Chr2 – consensus for side effects (exactly-once is a lie)

Summary

Chronon A deterministic, crash-safe distributed state machine with exactly-once side effects. Chronon is a Rust implementation of a replicated log and consensus engine designed for systems that cannot afford to lose data or execute side effects twice. It combines Viewstamped Replication (VSR) with a durable outbox pattern to guarantee exactly-once semantics even across crashes and leader failovers. Core Guarantees Property Guarantee Durability All committed entries survive any single-node failure Consistency Linearizable reads and writes via quorum consensus Exactly-Once Side effects execute exactly once, even after crashes Determinism Replicas converge to identical state from identical logs Architecture ┌─────────────────────────────────────────────────────────────────────┐ │ Chronon Node │ ├─────────────────────────────────────────────────────────────────────┤ │ ┌─────────────┐ ┌─────────────┐ ┌─────────────────────────┐ │ │ │ VSR Layer │───>│ Kernel │───>│ Application (Bank) │ │ │ │ (Consensus)│ │ (Executor) │ │ ChrApplication trait │ │ │ └─────────────┘ └─────────────┘ └─────────────────────────┘ │ │ │ │ │ │ │ ▼ ▼ ▼ │ │ ┌─────────────┐ ┌─────────────┐ ┌─────────────────────────┐ │ │ │ Log Writer │ │ Snapshots │ │ Durable Outbox │ │ │ │ (O_DSYNC) │ │ (Compaction)│ │ (Side Effects) │ │ │ └─────────────┘ └─────────────┘ └─────────────────────────┘ │ └─────────────────────────────────────────────────────────────────────┘ Control Plane vs Data Plane Chronon architecturally divorces the control plane (heartbeats, elections, view changes) from the data plane (log writes, durability). This ensures: Heartbeats are never blocked by disk I/O Elections don't trigger during transient disk stalls Tail latency on the data path doesn't cascade to cluster availability Key Components Storage Engine ( engine/ ) LogWriter : Append-only log with O_DSYNC for synchronous durability : Append-only log with for synchronous durability LogReader : Lock-free concurrent reads with visibility...