How do I log results from an Azure Function App dependency? - azure

Question

I have an Azure Function App project with the following files:
Startup.cs: Registers a dependency
[assembly: FunctionsStartup(typeof(MyLoggingFunction.Startup))]
namespace MyLoggingFunction
{
public class Startup : FunctionsStartup
{
public override void Configure(IFunctionsHostBuilder builder)
{
builder.Services.AddScoped<MyService>();
}
}
}
MyService.cs: Writes a log message
namespace MyLoggingFunction
{
public class MyService
{
private readonly ILogger<MyService> logger;
public MyService(ILogger<MyService> logger)
{
this.logger = logger;
}
public void Go()
{
this.logger.LogInformation("MyService.Go");
}
}
}
MyFunction.cs: The actual function; uses MyService
namespace MyLoggingFunction
{
public class MyFunction
{
private readonly MyService myService;
public MyFunction(MyService myService)
{
this.myService = myService;
}
[FunctionName("MyFunction")]
public IActionResult Run(
[HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)] HttpRequest req,
ILogger log)
{
log.LogInformation("C# HTTP trigger function processed a request.");
this.myService.Go();
log.LogInformation("All done");
return new OkObjectResult("Done.");
}
}
}
Here is the output visible in Azure after the function runs successfully. Note that the log message from the injected dependency is missing:
How do I get log messages from the dependency to show up as part of the built-in logging?

Answer 1

Add logging level entry to host.json :
{
"version": "2.0",
"logging": {
"logLevel": {
"default": "Information"
}
}
}

Answer 2

You must whitelist the classes and/or namespaces from which you want to allow logging. An example hosts.json file:
{
"logging": {
"logLevel": {
"MyLoggingFunction": "Information"
}
},
"version": "2.0"
}
This is documented as an issue on the azure-function-host GitHub repository.