Durable Task Scheduler
Build reliable, fault-tolerant workflows using durable execution with Azure Durable Task Scheduler.
When to Use
- Long-running workflows requiring state persistence
- Distributed transactions with compensating actions (saga pattern)
- Multi-step orchestrations with checkpointing
- Fan-out/fan-in parallel processing
- Workflows requiring human interaction or external events
- Stateful entities (aggregators, counters, state machines)
- Multi-agent AI orchestration
- Data processing pipelines
Framework Selection
| Framework | Best For | Hosting |
|---|---|---|
| Durable Functions | Serverless event-driven apps | Azure Functions |
| Durable Task SDKs | Any compute (containers, VMs) | Azure Container Apps, Azure Kubernetes Service, App Service, VMs |
💡 TIP: Use Durable Functions for serverless with built-in triggers. Use Durable Task SDKs for hosting flexibility.
Quick Start - Local Emulator
# Start the emulator (see https://mcr.microsoft.com/v2/dts/dts-emulator/tags/list for available versions)
docker pull mcr.microsoft.com/dts/dts-emulator:latest
docker run -d -p 8080:8080 -p 8082:8082 --name dts-emulator mcr.microsoft.com/dts/dts-emulator:latest
# Dashboard available at http://localhost:8082Workflow Patterns
| Pattern | Use When |
|---|---|
| Function Chaining | Sequential steps, each depends on previous |
| Fan-Out/Fan-In | Parallel processing with aggregated results |
| Async HTTP APIs | Long-running operations with HTTP polling |
| Monitor | Periodic polling with configurable timeouts |
| Human Interaction | Workflow pauses for external input/approval |
| Saga | Distributed transactions with compensation |
| Durable Entities | Stateful objects (counters, accounts) |
Connection & Authentication
| Environment | Connection String |
|---|---|
| Local Development (Emulator) | Endpoint=http://localhost:8080;Authentication=None;TaskHub=default |
| Azure (System-Assigned MI) | Endpoint=https://<scheduler>.durabletask.io;Authentication=ManagedIdentity;TaskHub=default |
| Azure (User-Assigned MI) | Endpoint=https://<scheduler>.durabletask.io;Authentication=ManagedIdentity;ClientID=<uami-client-id>;TaskHub=default |
⚠️ NOTE: Durable Task Scheduler uses identity-based authentication only — no connection strings with keys. When using a User-Assigned Managed Identity (UAMI), you must include the
ClientIDin the connection string.
Troubleshooting
| Error | Cause | Fix |
|---|---|---|
403 PermissionDenied on gRPC call (e.g., client.start_new()) |
Function App managed identity lacks RBAC on the Durable Task Scheduler resource, or IP allowlist blocks traffic | 1. Assign Durable Task Data Contributor role (0ad04412-c4d5-4796-b79c-f76d14c8d402) to the identity (SAMI or UAMI) scoped to the Durable Task Scheduler resource. For UAMI, also ensure the connection string includes ClientID=<uami-client-id>. 2. Ensure the scheduler's ipAllowlist includes 0.0.0.0/0 (an empty list denies all traffic). 3. RBAC propagation can take up to 10 minutes — restart the Function App after assigning roles. |
| Connection refused to emulator | Emulator container not running or wrong port | Verify container is running: docker ps and confirm port 8080 is mapped |
| 403 despite correct RBAC | Scheduler IP allowlist is empty (denies all) | Set ipAllowlist: ['0.0.0.0/0'] in Bicep or update via CLI: az durabletask scheduler update --ip-allowlist '0.0.0.0/0' |
| TaskHub not found | Task hub not provisioned or name mismatch | Ensure the TaskHub parameter in the DURABLE_TASK_SCHEDULER_CONNECTION_STRING matches the provisioned task hub name |
| 403 Forbidden on DTS dashboard | Deploying user lacks RBAC on the scheduler | Assign Durable Task Data Contributor role to your own user identity (not just the Function App MI) scoped to the scheduler resource — see Bicep Patterns for the dashboard role assignment snippet |
References
- .NET — packages, setup, examples, determinism, retry, SDK
- Python — packages, setup, examples, determinism, retry, SDK
- Java — dependencies, setup, examples, determinism, retry, SDK
- JavaScript — packages, setup, examples, determinism, retry, SDK
- Bicep Patterns — scheduler, task hub, RBAC, CLI provisioning
- Official Documentation
- Durable Functions Overview
- Sample Repository
- Choosing an Orchestration Framework