Reviewed by Aditya Kumar · Last reviewed 2026-03-24
**Why Durable:** Regular Functions are stateless—each invocation independent. Durable adds orchestration: chain steps, fan-out/fan-in, wait for external events. State persisted in Azure Storage. **Patterns:** (1) Function chaining: A→B→C. (2) Fan-out/fan-in: parallel calls,...
Why Durable: Regular Functions are stateless—each invocation independent. Durable adds orchestration: chain steps, fan-out/fan-in, wait for external events. State persisted in Azure Storage.
Patterns: (1) Function chaining: A→B→C. (2) Fan-out/fan-in: parallel calls, aggregate. (3) Human interaction: wait for approval. (4) Timers: durable delay.
Scalability: Durable uses replay—orchestrator re-runs from history; activities run once. At scale: many orchestrations, each with own state. Cost: storage for state; compute for activities. Use for multi-step ETL, approval workflows.
Trade-off: Regular Function = simple, cheap. Durable = complex workflows, worth the overhead.
Red Flag: Using Durable for single-step logic. Pro-Move: 'We use Durable for our 5-step data pipeline—checkpoint after each so we resume from last good step on failure.'
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