C# and .NET examples · Azure Functions

Azure Durable Functions: Hello World in C#

A minimal Azure Durable Functions v4 example in C# that runs a single-activity orchestration pipeline on the .NET 8 isolated worker. It is a good first step for learning how an HTTP starter (DurableTaskClient), an orchestrator (TaskOrchestrationContext), and an activity function work together. An HTTP trigger receives a JSON body, starts an orchestrator, and the orchestrator calls one activity that returns a personalised greeting.

In this guide: Get started · Walk through the example · Understand the details · Check the limits

✨ Features

Functions

Function	Trigger	Description
func-message-validator	HTTP POST	Reads request body, starts orchestration, waits for completion, returns result
func-message-orchestrator	Orchestration	Extracts name from JSON payload, calls func-say-hello
func-say-hello	Activity	Returns "Hello {name}!"

🚀 Quick start

Running Locally

cd Durable/DemoOne
func start --port 7239

📦 Prerequisites and installation

Requirements

• .NET 8 SDK
• Azure Functions Core Tools v4
• A local.settings.json file in the project root (not committed to source control)

Minimum local.settings.json

{
  "IsEncrypted": false,
  "Values": {
    "AzureWebJobsStorage": "UseDevelopmentStorage=true",
    "FUNCTIONS_WORKER_RUNTIME": "dotnet-isolated"
  }
}

Requires Azurite or a real Azure Storage connection string for durable task state.

NuGet Packages

Package	Version
Microsoft.Azure.Functions.Worker	2.0.0
Microsoft.Azure.Functions.Worker.Extensions.DurableTask	1.2.3
Microsoft.Azure.Functions.Worker.Extensions.Http	3.3.0
Microsoft.Azure.Functions.Worker.Extensions.Http.AspNetCore	2.0.1
Microsoft.Azure.Functions.Worker.Sdk	2.0.2

💡 Usage

curl -X POST http://localhost:7239/api/func-message-validator \
  -H "Content-Type: application/json" \
  -d '{"name": "Alice"}'

Expected greeting value (HTTP serialization is host-dependent and not runtime-verified here):

"Hello Alice!"

Empty body returns 400:

Request body cannot be empty.

🏗️ Architecture

POST /api/func-message-validator
          │
          ▼
 func-message-validator        (HTTP client trigger)
          │  schedules orchestration
          ▼
 func-message-orchestrator     (orchestrator)
          │  calls activity
          ▼
 func-say-hello                (activity — returns "Hello {name}!")

Project Structure

DemoOne/
├── Functions/
│   ├── FunctionClient.cs          # HTTP trigger — starts orchestration
│   ├── FunctionOrchestrator.cs    # Orchestrator — extracts name, calls activity
│   └── Triggers/
│       └── ModifyMessage.cs       # Activity (func-say-hello)
├── Properties/
│   └── launchSettings.json        # Default port: 7239
├── Program.cs                     # Host builder entry point
├── host.json
└── DemoOne.csproj

🧪 Development and testing

From the repository root, build with dotnet build Durable/DemoOne/DemoOne.csproj -p:Platform=x64. The project declares only the x64 platform; its solution’s Any CPU configurations map to x64 but omit the corresponding Build.0 entries, so select x64 or build the project explicitly when verifying it. In a configured local host, verify the greeting value, exact HTTP encoding and empty-body 400 response. Source and paths were checked; host execution was not performed.

🛠️ Troubleshooting and limitations

Notes

• The HTTP starter waits for the orchestration to finish (WaitForInstanceCompletionAsync) and returns the orchestration’s serialized output, so the value passed to OkObjectResult is already JSON-serialized text. The HTTP formatter can add further encoding; inspect a live response before relying on its exact wire format.
• Waiting within the HTTP request keeps the demo simple; the wait itself is asynchronous. For long-running workflows, return the orchestration status URLs instead (for example with CreateCheckStatusResponseAsync) and let the client poll.

Only an empty request body is rejected explicitly. Malformed JSON and a missing name are not validated as a complete API contract. The starter waits without an explicit timeout or cancellation token and does not inspect the orchestration failure status. The exact HTTP serialization has not been checked against a running host.

🔗 Related documentation

Related Examples

• DemoTwo — three chained activities with input validation
• Durable Functions overview
• Back to all C# and .NET code examples

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Documentation links

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