HowTo: Custom fields in ApplicationInsights

Sun, 25 Mar 2018 in windows, csharp, howto

Recently, I have shown, how to enable Application Insights within own WCF server application (look here). It might similarly work in other kinds of apps, so we won’t bother with further demystification of this procedure. But as you might suspect (or already stepped on), you will quickly require more metadata transmitted than it is done by default.

My scenario is pretty simple. The WCF server is installed multiple times, in multiple physical locations across the whole country. And they all just sit there, working since most of the bugs aren’t so critical. It can’t be even updated everywhere at the same time. So how to actually distinguish between different instances and app versions in case of a crash or other serious misbehaviors?

And the answer is – ITelemetryInitializer.

This kind of objects are responsible for performing initialization of the telemetry data gathered and then sent back to the Azure’s AppInsights service.

Here is the recipe, how to define and enable one in own project:

First create a class that implements ITelemetryInitializer interface.
Within Initialize() method, set additional context properties. To match my scenario, let it be two fields:

“ClientInstance” – to let know, which server it’s running on (yes, it should be read from external configuration file, but should be clear enough for now, as I hard-code it)
“BuildInfo” – to inform about application version running there, which I read directly from the assembly nameOf course the way it was obtained should be updated to match the logic in your app.

public sealed class ClientInstanceTelemetryInitializer : ITelemetryInitializer
{
    private const string ClientInstanceParam = "ClientInstance";
    private const string BuildInfoParam = "BuildInfo";

    private readonly string _instance;
    private readonly string _version;

    public ClientInstanceTelemetryInitializer()
    {
        _instance = "beaa9ac0-3267-41e4-9c14-2167271aca4d"; // should be different for each running instance
        _version = new AssemblyName(Assembly.GetExecutingAssembly().FullName).Version;
    }

    /// <inheritdoc />
    void ITelemetryInitializer.Initialize(ITelemetry telemetry)
    {
        telemetry.Context.Properties[ClientInstanceParam] = _instance;
        telemetry.Context.Properties[BuildInfoParam] = _version;
    }
}

Finally, register the initializer via ApplicationInsights.config file (this file was added automatically to the project, when AppInsights NuGet packages were installed inside the previous guide). Simply add the type at the end of TelemetryInitializers section. It will be instantiated automatically at application startup.

Telemetry Initializers