Did not find functions with language [dotnet-isolated].

Question

Did not find functions with language [dotnet-isolated].

Jibin Johnson 50

We recently migrated our Azure Functions to isolated process (running on .NET 6). This was tested in our DEV subscription where there were no host level issues reported. However, in our production subscription, the functions 'intermittently' report the error "Did not find functions with language [dotnet-isolated].". What we have noticed also is that the function host is shut down. You need to then access the function through Azure portal which activates the host. Please note that the issue is intermittent. The function does work fine for a while.

On a parallel note, since the isolated process deployment, on some of the functions we have noticed "A collision for Host ID 'functionsv4placeholdertemplatesi' was detected in the configured storage account. For more information, see https://aka.ms/functions-hostid-collision.".

Error details

Description : A host error has occurred during startup operation 'f228ae71-6bab-43db-9603-a6844fa77dab'.
Last offline at 8/6/2023 10:59:28 PM
Microsoft.Azure.WebJobs.Script.HostInitializationException : Did not find functions with language [dotnet-isolated]. at Microsoft.Azure.WebJobs.Script.Utility.VerifyFunctionsMatchSpecifiedLanguage(IEnumerable1 functions,String workerRuntime,Boolean isPlaceholderMode,Boolean isHttpWorker,CancellationToken cancellationToken) at //src/WebJobs.Script/Utility.cs : 627
at async Microsoft.Azure.WebJobs.Script.ScriptHost.GetFunctionDescriptorsAsync(IEnumerable1 functions,IEnumerable1 descriptorProviders,String workerRuntime,CancellationToken cancellationToken) at //src/WebJobs.Script/Host/ScriptHost.cs : 746
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at async Microsoft.Azure.WebJobs.Script.ScriptHost.InitializeFunctionDescriptorsAsync(IEnumerable1 functionMetadata,String workerRuntime,CancellationToken cancellationToken) at /_/src/WebJobs.Script/Host/ScriptHost.cs : 520 at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at async Microsoft.Azure.WebJobs.Script.ScriptHost.InitializeAsync(CancellationToken cancellationToken) at /_/src/WebJobs.Script/Host/ScriptHost.cs : 314 at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at async Microsoft.Azure.WebJobs.Script.ScriptHost.StartAsyncCore(CancellationToken cancellationToken) at /_/src/WebJobs.Script/Host/ScriptHost.cs : 256 at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at async Microsoft.Extensions.Hosting.Internal.Host.StartAsync(CancellationToken cancellationToken) at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at async Microsoft.Azure.WebJobs.Script.WebHost.WebJobsScriptHostService.UnsynchronizedStartHostAsync(ScriptHostStartupOperation activeOperation,Int32 attemptCount,JobHostStartupMode startupMode) at /_/src/WebJobs.Script.WebHost/WebJobsScriptHostService.cs : 328

Related information

Programming language - C#
.NET version - 6.0
Note : The functions are hosted in consumption plan. The app service plan hosts about 38 apps and they do use a shared storage account. However, each of these functions have unique host ids.

navba-MSFT 27,540 Reputation points Microsoft Employee Moderator

2023-08-07T04:24:46.1633333+00:00

@Jibin Johnson Welcome to Microsoft Q&A Forum, Thank you for posting your query here!

In the Azure Function App, Within the AppSettings, please set FUNCTIONS_WORKER_RUNTIME configuration value as "dotnet-isolated" as shown below:

This will restart the function app, in order for this new setting to take effect. Check if the error disappears after this.

Hope this helps.

**
Please do not forget to "Accept the answer” and “up-vote” wherever the information provided helps you, this can be beneficial to other community members.
Jibin Johnson 50 Reputation points

2023-08-07T04:30:12.0266667+00:00

Hi there, the app setting "FUNCTIONS_WORKER_RUNTIME" is already set to 'dotnet-isolated'.
navba-MSFT 27,540 Reputation points Microsoft Employee Moderator

2023-08-07T04:51:55.8333333+00:00
@Jibin Johnson Thanks for getting back. Here are a few more action plan which you can follow:

Firstly, ensure that you have the following basic files required in any .NET isolated project:

host.json file.

local.settings.json file.

C# project file (.csproj) that defines the project and dependencies.

Program.cs file that's the entry point for the app.

Any code files defining your functions.

Since you mentioned you already have the FUNCTIONS_WORKER_RUNTIME setting set to dotnet-isolated, Please restart the function-app once manually and check if you still encounter the same issue.

What is the value you have set for FUNCTIONS_WORKER_PROCESS_COUNT in your app settings ? The maximum value allowed is 10. By default, every Functions host instance has a single language worker process. You can increase the number of worker processes per host (up to 10) by using the FUNCTIONS_WORKER_PROCESS_COUNT application setting. Azure Functions then tries to evenly distribute simultaneous function invocations across these workers. More info here and here

On a side note, Sharing the storage account across multiple function apps isn't always a good idea in a production environment. You may need to use separate storage accounts to avoid host ID collisions.

I am also sharing a few threads which are relevant to this issue, if it helps:

https://learn.microsoft.com/en-us/answers/questions/51042/unable-to-get-function-host-running-with-the-follo
https://github.com/Azure/azure-functions-host/issues/7618
https://stackoverflow.com/questions/69104798/error-did-not-find-functions-with-language-dotnet-isolated-in-azure-function
https://stackoverflow.com/questions/68086787/azure-function-failed-to-start-a-new-language-worker-for-runtime-dotnet-isola

**
Please do not forget to "Accept the answer” and “up-vote” wherever the information provided helps you, this can be beneficial to other community members.
Jibin Johnson 50 Reputation points

2023-08-07T05:39:57.3966667+00:00
Thanks for your reply.

Here are my responses :

Ensure all basic files : Yes all of this are in place. local settings doesn't apply in a function deployed on Azure but we do use in local development. We followed the migration guide to move to isolated process.

We have not set any value for FUNCTIONS_WORKER_PROCESS_COUNT in app settings. Would increasing this have an impact on the issue with "Did not find functions with language [dotnet-isolated]."?

Shared storage account : Yes, aware of that. We have ensured host ids don't collide. However, we are working towards isolating.

Kindly note, the same function (in isolated process) works totally fine in our dev subscription/app service plan. Also, in the current app service plan, the issue is intermitted (4 errors in 24 hours).

We have gone through most of these links and tried the resolutions mentioned. We will try setting value for FUNCTIONS_WORKER_PROCESS_COUNT in app settings if you suggest that has any impact.
navba-MSFT 27,540 Reputation points Microsoft Employee Moderator

2023-08-07T05:45:06.4033333+00:00

@Jibin Johnson Thanks for your getting back and sharing a quick update. Please try setting the FUNCTIONS_WORKER_PROCESS_COUNT appsetting to the value starting from 5 and then you can slowly increase it up to MAX 10. Then please restart the function app manually and check again.
Jibin Johnson 50 Reputation points

2023-08-07T10:25:13.84+00:00

I did as suggested. It worked for a while, but, then produced an error - "Failed to start a new language worker for runtime: dotnet-isolated."
navba-MSFT 27,540 Reputation points Microsoft Employee Moderator

2023-08-07T12:15:46.0133333+00:00
@Jibin Johnson Thanks for getting back. I am glad that the actual issue reported earlier is not occurring anymore.

This new error message Failed to start a new language worker for runtime: dotnet-isolated indicates that the Azure Functions runtime was unable to start a new instance of the .NET Isolated Process language worker. This can be caused by a number of issues, including missing dependencies, configuration issues, or problems with the Azure Functions runtime itself.

Here are a few things you can try to resolve this issue:

Firstly, please check the storage connectivity. Refer this.

If Function is connected over VNET then follow : https://learn.microsoft.com/en-us/azure/azure-functions/configure-networking-how-to?tabs=portal

Check if you are using most recent version of functions worker package:
Microsoft.Azure.Functions.Worker.
See this: https://www.nuget.org/packages/Microsoft.Azure.Functions.Worker/1.18.0 More info here.

Check your dependencies: Make sure that all of the dependencies required by your Azure Function are installed and up-to-date. This includes the .NET Core runtime, the Azure Functions Core Tools, and any other packages or libraries that your function depends on. For example if you are using the package Microsoft.WindowsAzure.Storage.blobs instead of Azure.Storage.Blobs in your project depend upon the code then you could observe the issue.

Check for updates: Make sure that you are running the latest version of the Azure Functions runtime and the .NET Isolated Process language worker. You can check for updates using the Azure Functions Core Tools or by checking the Azure Functions documentation.

In case if you still observe the issue then please share the sample project so we can review it at our end. Awaiting your reply.
Jibin Johnson 50 Reputation points

2023-08-08T00:26:27.4866667+00:00
Hi there, the 'actual issue' (Did not find functions with language [dotnet-isolated].) is not yet resolved. Adding "FUNCTIONS_WORKER_PROCESS_COUNT" has caused an additional error to occur " The operation has timed out - Failed to start a new language worker for runtime: dotnet-isolated".

We don't use any VNET. The storage is co-located in the same region. We have run network utility and ping tests from the app to check connection to storage.

Worker packages are at the latest version.

We have repeatedly checked and ensured that all the dependencies are referenced.

We do use the latest versions of Azure Function Core tools for our 'local development'

We'd like to highlight

The issue does not occur during local development, it only occurs on the function deployed in Azure

The same function is running exception free in another Azure subscription (our development Azure subscription).

In our Production Azure Subscription (where the issue occurs), the issue is 'intermittent'. We get about 4-5 exceptions in a period of 24 hours. We have been checking the function executions and they aren't impacted. There's only 1-2 instances in the last 7 days where we found the host was completely shut down.

We assume, had it been a source code issue, the function should not have been running at all (in any deployed subscription)
navba-MSFT 27,540 Reputation points Microsoft Employee Moderator

2023-08-08T05:21:58.62+00:00
@Jibin Johnson Thanks for getting back and sharing an update.

Please share the below details over an email at AzCommunity@microsoft.com ( with subject "Attn: Naveen") and include the below details:

Your Azure Function Name

You Azure Function App resource URI in below format:
/subscriptions/XXXXXXXXXX/resourceGroups/XXXXXX/providers/Microsoft.Web/sites/XXXXXX

Most recent UTC time of the actual issue *Did not find functions with language [dotnet-isolated]*

I will look at the backend logs to identify the root cause.

Awaiting your reply.

Accepted answer

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Your answer

navba-MSFT 27,540 Reputation points Microsoft Employee Moderator

2023-08-07T04:24:46.1633333+00:00

@Jibin Johnson Welcome to Microsoft Q&A Forum, Thank you for posting your query here!

In the Azure Function App, Within the AppSettings, please set FUNCTIONS_WORKER_RUNTIME configuration value as "dotnet-isolated" as shown below:

This will restart the function app, in order for this new setting to take effect. Check if the error disappears after this.

Hope this helps.

**
Please do not forget to "Accept the answer” and “up-vote” wherever the information provided helps you, this can be beneficial to other community members.
Jibin Johnson 50 Reputation points

2023-08-07T04:30:12.0266667+00:00

Hi there, the app setting "FUNCTIONS_WORKER_RUNTIME" is already set to 'dotnet-isolated'.
Jibin Johnson 50 Reputation points

2023-08-07T05:39:57.3966667+00:00

Thanks for your reply.

Here are my responses :

Ensure all basic files : Yes all of this are in place. local settings doesn't apply in a function deployed on Azure but we do use in local development. We followed the migration guide to move to isolated process.

We have not set any value for FUNCTIONS_WORKER_PROCESS_COUNT in app settings. Would increasing this have an impact on the issue with "Did not find functions with language [dotnet-isolated]."?

Shared storage account : Yes, aware of that. We have ensured host ids don't collide. However, we are working towards isolating.

Kindly note, the same function (in isolated process) works totally fine in our dev subscription/app service plan. Also, in the current app service plan, the issue is intermitted (4 errors in 24 hours).

We have gone through most of these links and tried the resolutions mentioned. We will try setting value for FUNCTIONS_WORKER_PROCESS_COUNT in app settings if you suggest that has any impact.
navba-MSFT 27,540 Reputation points Microsoft Employee Moderator

2023-08-07T05:45:06.4033333+00:00

@Jibin Johnson Thanks for your getting back and sharing a quick update. Please try setting the FUNCTIONS_WORKER_PROCESS_COUNT appsetting to the value starting from 5 and then you can slowly increase it up to MAX 10. Then please restart the function app manually and check again.
Jibin Johnson 50 Reputation points

2023-08-07T10:25:13.84+00:00

I did as suggested. It worked for a while, but, then produced an error - "Failed to start a new language worker for runtime: dotnet-isolated."
navba-MSFT 27,540 Reputation points Microsoft Employee Moderator

2023-08-07T12:15:46.0133333+00:00

@Jibin Johnson Thanks for getting back. I am glad that the actual issue reported earlier is not occurring anymore.

This new error message Failed to start a new language worker for runtime: dotnet-isolated indicates that the Azure Functions runtime was unable to start a new instance of the .NET Isolated Process language worker. This can be caused by a number of issues, including missing dependencies, configuration issues, or problems with the Azure Functions runtime itself.

Here are a few things you can try to resolve this issue:

Firstly, please check the storage connectivity. Refer this.

If Function is connected over VNET then follow : https://learn.microsoft.com/en-us/azure/azure-functions/configure-networking-how-to?tabs=portal

Check if you are using most recent version of functions worker package:
Microsoft.Azure.Functions.Worker.
See this: https://www.nuget.org/packages/Microsoft.Azure.Functions.Worker/1.18.0 More info here.

Check your dependencies: Make sure that all of the dependencies required by your Azure Function are installed and up-to-date. This includes the .NET Core runtime, the Azure Functions Core Tools, and any other packages or libraries that your function depends on. For example if you are using the package Microsoft.WindowsAzure.Storage.blobs instead of Azure.Storage.Blobs in your project depend upon the code then you could observe the issue.

Check for updates: Make sure that you are running the latest version of the Azure Functions runtime and the .NET Isolated Process language worker. You can check for updates using the Azure Functions Core Tools or by checking the Azure Functions documentation.

In case if you still observe the issue then please share the sample project so we can review it at our end. Awaiting your reply.
Jibin Johnson 50 Reputation points

2023-08-08T00:26:27.4866667+00:00

Hi there, the 'actual issue' (Did not find functions with language [dotnet-isolated].) is not yet resolved. Adding "FUNCTIONS_WORKER_PROCESS_COUNT" has caused an additional error to occur " The operation has timed out - Failed to start a new language worker for runtime: dotnet-isolated".

We don't use any VNET. The storage is co-located in the same region. We have run network utility and ping tests from the app to check connection to storage.

Worker packages are at the latest version.

We have repeatedly checked and ensured that all the dependencies are referenced.

We do use the latest versions of Azure Function Core tools for our 'local development'

We'd like to highlight

The issue does not occur during local development, it only occurs on the function deployed in Azure

The same function is running exception free in another Azure subscription (our development Azure subscription).

In our Production Azure Subscription (where the issue occurs), the issue is 'intermittent'. We get about 4-5 exceptions in a period of 24 hours. We have been checking the function executions and they aren't impacted. There's only 1-2 instances in the last 7 days where we found the host was completely shut down.

We assume, had it been a source code issue, the function should not have been running at all (in any deployed subscription)
navba-MSFT 27,540 Reputation points Microsoft Employee Moderator

2023-08-08T05:21:58.62+00:00

@Jibin Johnson Thanks for getting back and sharing an update.

Please share the below details over an email at AzCommunity@microsoft.com ( with subject "Attn: Naveen") and include the below details:

Your Azure Function Name

You Azure Function App resource URI in below format:
/subscriptions/XXXXXXXXXX/resourceGroups/XXXXXX/providers/Microsoft.Web/sites/XXXXXX

Most recent UTC time of the actual issue *Did not find functions with language [dotnet-isolated]*

I will look at the backend logs to identify the root cause.

Awaiting your reply.

Answer 1

@Jibin Johnson We appreciate your patience on this. The Microsoft Azure Functions Team has investigated the issue you reported on your Function Apps, where your functions stopped processing new invocations. This issue was mitigated by browsing the Function App in the Azure Portal.

Upon investigation, engineers discovered that after a regular scale in operation in response to Function App configured triggers, one of the instances was in an unhealthy state. The scale controller kept monitoring the healthiness of the Function App, however, was not able to determine with enough confidence that the unhealthy instance had to be removed.

Further investigation on the unhealthy instance showed that due to a race condition on the scale operation, after the Functions Runtime failed to start with "Did not find functions with language [dotnet-isolated]", it couldn't automatically recover as expected when it detects such errors as part of Function App initialization.

Once the Function App was browsed in the Azure Portal, the process started properly and your functions started processing invocations.

We are continuously taking steps to improve the Azure Functions service and our processes to ensure such incidents do not occur in the future, and in this case it includes (but is not limited to):

Improve the Function App Health Checks and trigger monitoring to ensure invocations are not missed due to unhealthy instances
Ensure Placeholders are completely initialized before they are specialized: https://github.com/Azure/azure-functions-host/issues/9444

Please keep the track of the fix here: https://github.com/Azure/azure-functions-host/issues/9477

This has the fix mitigation to address this issue due to race condition.

We apologize for any inconvenience.

Regards,

The Microsoft Azure Team

**
Please do not forget to "Accept the answer” and “up-vote” wherever the information provided helps you, this can be beneficial to other community members.

Jibin Johnson 50 Reputation points

2023-08-24T03:29:19.9233333+00:00

Thank you so much for getting back to us. Looking forward to this being fixed.

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Did not find functions with language [dotnet-isolated].

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