Is it possible to ensure an Azure Function executes only once in parallel?

Question

I have the requirement to execute an Azure Function (let's call it OperationalFunction) only once in parallel. What I mean is the following:

I have two "entry point" functions:

I have a BlobTrigger Function (BlobTriggeredStartFunction) I have a HttpTrigger Function (HttpTriggeredStartFunction) Both of those functions call an orchestrator function (OrchestratorFunction) like this:

string instanceId = await starter.StartNewAsync(nameof(OrchestrationFunction),null,data);

This orchestration function has the following code:

[FunctionName("OrchestrationFunction")]
public async Task OrchestrationFunction(
[OrchestrationTrigger] IDurableOrchestrationContext context){
   var input = context.GetInput<string>();
   await context.CallActivityAsync(nameof(OperationalFunction),input);
}

I want that the *OperationalFunction *is executed ONLY ONCE in parallel, so that if I receive multiple triggers (n blob/http-triggered events), the *OperationalFunction *at a certain time, is executing only one instance, when such instance finishes, then the new event in the queue (FIFO) is executed.

Which is the best approach to that?

I tried to edit the host.json file by adding:

    "blobs": {
      "maxDegreeOfParallelism": 1,
      "poisonBlobThreshold": 1
    }

But it is not exactly what I am looking for, just a part of the problem is solved.

I also tried to add a loop do...while for getting the status of the orchestrator:

                do {
                    status = await starter.GetStatusAsync(instanceId);
                    await Task.Delay(2000);
                }
                while (
                    status.RuntimeStatus == OrchestrationRuntimeStatus.Running || 
                    status.RuntimeStatus == OrchestrationRuntimeStatus.Pending);

But I don't think this is the most efficient solution.

@RB-D4S Set a fixed InstanceId for the orchestrator and use GetStatusAsync to check its status. Start a new instance only if the existing one is completed, failed, or terminated. — Dasari Kamali
– Dasari Kamali, Commented Dec 5, 2024 at 4:59

Dasari Kamali · Accepted Answer · 2024-12-10 07:42:21Z

I created a sample Durable Orchestration with two triggers (Blob trigger and HTTP trigger) and successfully executed the OperationalFunction only once in parallel.

By configuring the settings below in host.json, we can ensure that OperationalFunction runs only one instance at a time across all triggers.

  "durableTask": {
    "maxConcurrentActivityFunctions": 1,
    "maxConcurrentOrchestrations": 1
  }

Below is the complete code for the durable orchestration using both Blob trigger and HTTP trigger functions.

HttpTriggeredStartFunction.cs :

using Microsoft.AspNetCore.Mvc;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.DurableTask;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
using System.IO;
using System.Threading.Tasks;
using Microsoft.Azure.WebJobs.Extensions.Http;

namespace FunctionApp5.Triggers
{
    public class HttpTriggeredStartFunction
    {
        [FunctionName("HttpTriggeredStartFunction")]
        public async Task<IActionResult> RunAsync(
            [HttpTrigger(AuthorizationLevel.Function, "post", Route = null)] HttpRequest req,
            [DurableClient] IDurableOrchestrationClient starter,
            ILogger log)
        {
            log.LogInformation("HTTP Triggered start function hit.");
            string requestData = await new StreamReader(req.Body).ReadToEndAsync();
            await starter.StartNewAsync("OrchestrationFunction", null, requestData);
            return new OkObjectResult("HTTP orchestration started successfully.");
        }
    }
}

BlobTriggeredStartFunction.cs :

using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.DurableTask;
using Microsoft.Extensions.Logging;
using System.IO;
using System.Threading.Tasks;

namespace FunctionApp5.Triggers
{
    public class BlobTriggeredStartFunction
    {
        [FunctionName("BlobTriggeredStartFunction")]
        public async Task RunAsync(
            [BlobTrigger("kamcontainer/{name}", Connection = "AzureWebJobsStorage")] Stream blobStream,
            [DurableClient] IDurableOrchestrationClient starter,
            ILogger log)
        {
            log.LogInformation($"Blob trigger received for: {blobStream}");
            await starter.StartNewAsync("OrchestrationFunction", null, "blob-data");
        }
    }
}

OperationalFunction.cs :

using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.DurableTask;
using Microsoft.Extensions.Logging;
using System.Threading.Tasks;

namespace FunctionApp5.Activities
{
    public class OperationalFunction
    {
        [FunctionName("OperationalFunction")]
        public async Task<string> RunAsync([ActivityTrigger] string input, ILogger log)
        {
            log.LogInformation($"OperationalFunction execution started with input: {input}");
            await Task.Delay(5000);
            log.LogInformation("OperationalFunction execution finished.");
            return "Success";
        }
    }
}

OrchestrationFunction.cs :

using System.Threading.Tasks;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.DurableTask;
using Microsoft.Extensions.Logging;

namespace FunctionApp5.Orchestrator
{
    public class OrchestrationFunction
    {
        [FunctionName("OrchestrationFunction")]
        public async Task OrchestrationFunctionAsync(
            [OrchestrationTrigger] IDurableOrchestrationContext context,
            ILogger log)
        {
            log.LogInformation("Starting orchestration.");
            var input = context.GetInput<string>();
            await context.CallActivityAsync<string>("OperationalFunction", input);
            log.LogInformation("Operational Function finished execution.");
        }
    }
}

Output :

The Durable Orchestration function executed successfully, and the logs from the Blob trigger function were displayed as shown below.

enter image description here

I successfully sent a POST request to the HTTP trigger function using Postman, as shown below.

enter image description here

I got below function logs after post request.

enter image description here

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