Application Insights with multiple applications

Question

I have an Application Insights which logs traces from an App Service and an App Function (one resource for 2 functions). I need to filter traces according to the resource (App Service or App Function) and, if possible, for the App Function which function is actually logging. Looking at the traces I see the following list of properties:

I thought to find the resource name in the appName property, instead there is the Application Insights resource name, which is useless for me, since all those traces are from that resource.

Note: I don't like the workaround to set a prefix in the message to filter the traces.

UPDATE

I followed Peter Bons suggestions and I created a brand new Function V3 project. The basic version of the project worked also without the Telemetry Initializer, I mean that the Cloud_RoleName property was correctly populated. Then, I added my changes to adapt the sample code and I found that the problem comes up when I inject a new Telemetry Client. I know, it is not recommended to manually inject TelemetryClient in App Function, but I absolutely need to send Custom Event to Application Insights and, as far as I know, it is not possible with ILogger interface used by default in App Function.

Startup.cs

public class Startup : FunctionsStartup
{
    private TelemetryConfiguration telemetryConfiguration;

    public override void Configure(IFunctionsHostBuilder builder)
    {
        var localRoot = Environment.GetEnvironmentVariable("AzureWebJobsScriptRoot");
        var azureRoot = $"{Environment.GetEnvironmentVariable("HOME")}/site/wwwroot";

        var configBuilder = new ConfigurationBuilder()
            .SetBasePath(localRoot ?? azureRoot)
            .AddEnvironmentVariables()
            .AddJsonFile("local.settings.json", optional: true, reloadOnChange: true);

        var configuration = configBuilder.Build();

        if (builder != null)
        {
            this.ConfigureServices(builder.Services, configuration);
        }
    }

    private void ConfigureServices(IServiceCollection services, IConfiguration configuration)
    {
        services.AddSingleton<ITelemetryInitializer>(x => new CustomTelemetryInitializer(configuration["appFunctionName"]));
        telemetryConfiguration = new TelemetryConfiguration(configuration["APPINSIGHTS_INSTRUMENTATIONKEY"]);
        telemetryConfiguration.TelemetryInitializers.Add(new OperationCorrelationTelemetryInitializer());
        var telemetryClient = new TelemetryClient(telemetryConfiguration);
        services.AddSingleton(telemetryClient);

        services.AddSingleton<ISampleInterface, SampleService>();
    }
}

CustomTelemetryInitializer.cs

public class CustomTelemetryInitializer : ITelemetryInitializer
{
    private readonly string roleName;

    public CustomTelemetryInitializer(string roleName)
    {
        this.roleName = roleName;
    }

    public void Initialize(ITelemetry telemetry)
    {
        if (string.IsNullOrEmpty(telemetry?.Context?.Cloud?.RoleName))
        {
            telemetry.Context.Cloud.RoleName = roleName;
        }
    }
}

SampleService.cs

public class SampleService : ISampleInterface
{
    private TelemetryClient telemetryClient;

    public SampleService(TelemetryClient telemetryClient)
    {
        this.telemetryClient = telemetryClient;
    }

    public void TestAppInsights()
    {
        telemetryClient.TrackEvent("Sample Custom Event with init");
        telemetryClient.TrackTrace("Sample Custom Trace with init");
    }
}

Function.cs

public class Function1
{
    private ISampleInterface service;
    public Function1(ISampleInterface service)
    {
        this.service = service;
    }

    [FunctionName("Function1")]
    public async Task<IActionResult> Run(
        [HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)] HttpRequest req,
        ILogger log)
    {
        log.LogInformation("C# HTTP trigger function processed a request with init.");

        this.service.TestAppInsights();

        string name = req.Query["name"];

        string requestBody = await new StreamReader(req.Body).ReadToEndAsync();
        dynamic data = JsonConvert.DeserializeObject(requestBody);
        name = name ?? data?.name;

        string responseMessage = string.IsNullOrEmpty(name)
            ? "This HTTP triggered function executed successfully. Pass a name in the query string or in the request body for a personalized response."
            : $"Hello, {name}. This HTTP triggered function executed successfully.";

        return new OkObjectResult(responseMessage);
    }
}

Answer 1

How about inspecting the cloud_RoleName property, available to all telemetry? By default it will have the name of the webapp or function (including slot names) as the value.

Otherwise, if you want to add custom properties or modify properties for all telemetry at one place you can make use of a telemetry initializer as demonstrated here:

using Microsoft.ApplicationInsights.Channel;
using Microsoft.ApplicationInsights.Extensibility;

namespace CustomInitializer.Telemetry
{
    public class MyTelemetryInitializer : ITelemetryInitializer
    {
        public void Initialize(ITelemetry telemetry)
        {
            telemetry.Context.Cloud.RoleName = "HttpTriggered";
        }
    }
}

This avoids having to prefix all traces as you mentioned as a work around by having a single piece of code all telemetry passes through:

Another thing

[...] but I absolutely need to send Custom Event to Application Insights and, as far as I know, it is not possible with ILogger interface used by default in App Function.

Do note that you can redirect the output emitted by using the ILogger interface to Application Insights. It will show up as a trace.