This warning occurs if the Azure function app is not able to detect the expected configuration for the function runtime i.e., if Function app's host is unable to determine the correct language or language runtime stack.
To resolve this,`FUNCTIONS_WORKER_RUNTIME` is a required setting, set it explicitly in all of the existing function apps to prevent any downtime.
when running the function locally, add the setting in `local.settings.json`, and under environment variables in portal.
**local.settings.json:**
```json
{
"IsEncrypted": false,
"Values": {
"AzureWebJobsStorage": "UseDevelopmentStorage=true",
"FUNCTIONS_WORKER_RUNTIME": "dotnet-isolated"
}
}
```
**Check if you have multiple `FUNCTIONS_WORKER_RUNTIME` settings added in the function app's App Settings.**
After adding `FUNCTIONS_WORKER_RUNTIME` in the `Function app=>Environment variables`, restart the Function App to ensure changes reflects.
- Go to the "Overview" section of your Function App and click on "Restart".
Upgrade the packages to the latest version and make sure the versions are compatible with .NET 8.0 isolated.
It could be due to the database connection issue as mentioned in [GitHub issue](https://github.com/MicrosoftDocs/azure-docs/issues/66877#issuecomment-813377228).
- Set the Target Framework to`.NET 8.0` and `FUNCTIONS_WORKER_RUNTIME:dotnet-isolated`.
- Delete the `AzureFunctionsTools` folder under `C:\Users\uname\AppData\Local` and restart the visual studio again.
**.csproj:**
```xml
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<TargetFramework>net8.0</TargetFramework>
<AzureFunctionsVersion>v4</AzureFunctionsVersion>
<OutputType>Exe</OutputType>
<ImplicitUsings>enable</ImplicitUsings>
<Nullable>enable</Nullable>
</PropertyGroup>
<ItemGroup>
<FrameworkReference Include="Microsoft.AspNetCore.App" />
<PackageReference Include="Microsoft.Azure.Functions.Worker" Version="1.21.0" />
<PackageReference Include="Microsoft.Azure.Functions.Worker.Extensions.Http" Version="3.1.0" />
<PackageReference Include="Microsoft.Azure.Functions.Worker.Extensions.Http.AspNetCore" Version="1.2.0" />
<PackageReference Include="Microsoft.Azure.Functions.Worker.Sdk" Version="1.17.0" />
<PackageReference Include="Microsoft.ApplicationInsights.WorkerService" Version="2.22.0" />
<PackageReference Include="Microsoft.Azure.Functions.Worker.ApplicationInsights" Version="1.2.0" />
</ItemGroup>
<ItemGroup>
<None Update="host.json">
<CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
</None>
<None Update="local.settings.json">
<CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
<CopyToPublishDirectory>Never</CopyToPublishDirectory>
</None>
</ItemGroup>
<ItemGroup>
<Using Include="System.Threading.ExecutionContext" Alias="ExecutionContext" />
</ItemGroup>
</Project>
```
**local.settings.json:**
```json
{
"IsEncrypted": false,
"Values": {
"AzureWebJobsStorage": "UseDevelopmentStorage=true",
"FUNCTIONS_WORKER_RUNTIME": "dotnet-isolated"
}
}
```
**Program.cs:**
```csharp
var host = new HostBuilder()
.ConfigureFunctionsWebApplication()
.ConfigureServices(services =>
{ services.AddApplicationInsightsTelemetryWorkerService();
services.ConfigureFunctionsApplicationInsights();
})
.Build();
host.Run();
```
