Visual Studio: New Durable Functions Project: System.InvalidOperationException: Synchronous operations are disallowed

When creating a new Azure Function App Project and selecting Durable Functions Orchestration, right now the basic functionality is erroring out when the default Http Function is triggered.

Error: System.InvalidOperationException: Synchronous operations are disallowed. Call WriteAsync or set AllowSynchronousIO to true instead.

Unfortunately, this is a known issue (https://github.com/Azure/azure-functions-dotnet-worker/issues/2425) with the templates and hopefully, the templates will get updated soon.

For the time being, you can update the code in the HttpStart function to use CreateCheckStatusResponseAsync as follows.

[Function("Function1_HttpStart")]
public static async Task<HttpResponseData> HttpStart(
    [HttpTrigger(AuthorizationLevel.Anonymous, "get", "post")] HttpRequestData req,
    [DurableClient] DurableTaskClient client,
    FunctionContext executionContext)
{
    ILogger logger = executionContext.GetLogger("Function1_HttpStart");
 
    // Function input comes from the request content.
    string instanceId = await client.ScheduleNewOrchestrationInstanceAsync(
        nameof(Function1));
 
    logger.LogInformation("Started orchestration with ID = '{instanceId}'.", instanceId);
 
    // Returns an HTTP 202 response with an instance management payload.
    // See https://learn.microsoft.com/azure/azure-functions/durable/durable-functions-http-api#start-orchestration
    return await client.CreateCheckStatusResponseAsync(req, instanceId);
}

Hope this helps.

Happy Coding.

Regards,

Jaliya