azure-prepare/references/services/functions/durable.md

Durable Functions

Long-running orchestrations with checkpointing and state management.

Storage Backend

Durable Functions requires a storage backend to persist orchestration state, queues, and history.

Backend	Recommendation	Notes
Durable Task Scheduler	✅ Required	Fully managed Azure service. Best performance, lowest latency, built-in monitoring. Supports all languages (.NET, Python, Java, JavaScript).
Azure Storage (default)	⛔ Do not use	Legacy backend. Higher latency, harder to monitor, no built-in RBAC. Not permitted for new projects.
MSSQL	Specialized	SQL Server backend. Only when SQL infrastructure already exists and user explicitly requests it.

⛔ MANDATORY: You MUST use Durable Task Scheduler as the storage backend for ALL new Durable Functions projects. Do NOT use Azure Storage as the backend — it is legacy and not permitted. Generate the DTS Bicep module (Microsoft.DurableTask/schedulers + taskHubs), RBAC role assignment (Durable Task Data Contributor), and DURABLE_TASK_SCHEDULER_CONNECTION_STRING app setting. See the Durable Task Scheduler reference for setup, language-specific guidance, and Bicep templates.

When to Use

• Multi-step workflows
• Fan-out/fan-in patterns
• Human interaction workflows
• Long-running processes

Get Durable Templates

Use the Azure Functions Templates workflow to discover and fetch durable samples:

MCP Tool: functions_template_get(language) → filter resource == "durable"

Fallback: CDN manifest → filter resource == "durable"

Available patterns: Fan-out/Fan-in, Order Processing (with Bicep), Distributed Tracing, Large Payload, Saga, AI Travel Planner, PDF Summarizer, .NET Aspire integration.