Getting "Failed to start a new language worker for runtime" error when running durable function.

Question

We have deployed a durable function to the Function App service and are getting the following error in the log when we run it.

2023-07-20T13:17:07.338 [Error] Failed to start a new language worker for runtime: java.System.Threading.Tasks.TaskCanceledException : A task was canceled.at async Microsoft.Azure.WebJobs.Script.Grpc.GrpcWorkerChannel.StartWorkerProcessAsync(CancellationToken cancellationToken) at //src/WebJobs.Script.Grpc/Channel/GrpcWorkerChannel.cs : 275at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()at async Microsoft.Azure.WebJobs.Script.Workers.Rpc.RpcFunctionInvocationDispatcher.InitializeJobhostLanguageWorkerChannelAsync(??) at //src/WebJobs.Script/Workers/Rpc/FunctionRegistration/RpcFunctionInvocationDispatcher.cs : 152at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()at async Microsoft.Azure.WebJobs.Script.Workers.Rpc.RpcFunctionInvocationDispatcher.InitializeJobhostLanguageWorkerChannelAsync(??) at //src/WebJobs.Script/Workers/Rpc/FunctionRegistration/RpcFunctionInvocationDispatcher.cs : 144at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()at async Microsoft.Azure.WebJobs.Script.Workers.Rpc.RpcFunctionInvocationDispatcher.InitializeJobhostLanguageWorkerChannelAsync(??) at //src/WebJobs.Script/Workers/Rpc/FunctionRegistration/RpcFunctionInvocationDispatcher.cs : 135at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()at async Microsoft.Azure.WebJobs.Script.Workers.Rpc.RpcFunctionInvocationDispatcher.<>c__DisplayClass55_0.<StartWorkerProcesses>b__0(??) at /_/src/WebJobs.Script/Workers/Rpc/FunctionRegistration/RpcFunctionInvocationDispatcher.cs : 215

We had deployed the same code two weeks ago and it ran with no errors.

In the interim we deployed different code without the new durable function and have now deployed the code from two weeks ago again to test. Upon redeploying the code that was working two weeks ago, we have begun to see this issue.

Our function app service is set to runtime ~4 with runtime version 4.19.0.20414

Answer 1

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

I see that you are encountering the error Failed to start a new language worker for runtime after deploying your Azure Function App.

• Which runtime stack are you using (.NET / Java ) ? And what is its corresponding runtime stack version you are using ?
• Could you please confirm if your Function App works fine locally (before uploading to Azure) in your Dev environment ?
• Please let us know if your Function App is within VNET ? If Yes, ensure that you have followed the below articles:
  https://learn.microsoft.com/en-us/azure/azure-functions/configure-networking-how-to?source=recommendations&tabs=portal
  https://learn.microsoft.com/en-us/azure/azure-functions/configure-networking-how-to?tabs=portal#restrict-your-storage-account-to-a-virtual-network

There are similar issues reported in the past. I am sharing those threads also here if that helps:
[https://learn.microsoft.com/en-us/answers/questions/1121514/i-have-an-error-(failed-to-start-a-new-language-wo](https://learn.microsoft.com/en-us/answers/questions/1121514/i-have-an-error-(failed-to-start-a-new-language-wo)
https://stackoverflow.com/questions/68086787/azure-function-failed-to-start-a-new-language-worker-for-runtime-dotnet-isola
https://github.com/Azure/azure-functions-dotnet-worker/issues/532
https://github.com/Azure/azure-functions-dotnet-worker/issues?q=is%3Aissue+%22Failed+to+start+a+new+language+worker+for+runtime%22+in%3Abody+is%3Aclosed

Awaiting your reply.