1 Core Architectural Concepts
Durable Execution
Code execution state (variables, call stack, timers) is persisted automatically across network outages, container restarts, and database failovers without manual checkpoints.
Workflows vs. Activities
Workflows orchestrate logic deterministically. Activities execute non-deterministic operations (calling LLM APIs, DB writes, scraping) with automated retry policies.
Deterministic Replay
When a worker crashes, a new worker reconstructs identical state by replaying past events from the append-only event history log, skipping already executed activities.
Signals & Human Approval
Workflows can sleep asynchronously for hours or days waiting for an external Signal (e.g. human manager approving a $10,000 refund) without holding active server memory.