Serilog.Sinks.ApplicationInsights   

A sink for Serilog that writes events to Microsoft Application Insights. This sink comes with several defaults that send Serilog LogEvent messages to Application Insights as either EventTelemetry or TraceTelemetry.

Install

dotnet add package Serilog.Sinks.ApplicationInsights

Configuring

The recommended way to configure the sink is to reuse the TelemetryConfiguration (or TelemetryClient) already configured by your application (for example via dependency injection in ASP.NET Core, Azure Functions, Worker Services).

Log.Logger = new LoggerConfiguration()
    .WriteTo.ApplicationInsights(
        telemetryConfiguration, // from DI (recommended)
        TelemetryConverter.Traces)
    .CreateLogger();

If you don't have an existing TelemetryConfiguration (uncommon), you can use the connection string overload:

Log.Logger = new LoggerConfiguration()
    .WriteTo.ApplicationInsights(
        "<your Application Insights connection string>",
        TelemetryConverter.Traces)
    .CreateLogger();

Legacy: some older application types used TelemetryConfiguration.Active. This is not recommended on modern .NET and may be deprecated depending on the Application Insights SDK version.

You can also pass an instrumentation key and this sink will create a new TelemetryConfiguration based on it, however it's actively discouraged compared to using already initialised telemetry configuration, as your telemetry won't be properly correlated.

Note: Whether you choose Events or Traces, if the LogEvent contains any exceptions it will always be sent as ExceptionTelemetry.

TelemetryConfiguration.Active is deprecated in the App Insights SDK for .NET Core, what do I do?

The singleton TelemetryConfiguration.Active has been deprecated in the Application Insights SDK on .NET Core in favor of dependency injection pattern .

Therefore, now we need to pass in the TelemetryConfiguration instance that was added either by services.AddApplicationInsightsTelemetryWorkerService() (if you're developing a non-http application) or services.AddApplicationInsightsTelemetry() (if you're developing an ASP.Net Core application) during Startup in ConfigureServices.

Log.Logger = new LoggerConfiguration()
    .WriteTo.ApplicationInsights(
        serviceProvider.GetRequiredService<TelemetryConfiguration>(),
        TelemetryConverter.Traces)
    .CreateLogger();

However, you probably want to setup your Logger as close to the entry point of your application as possible, so that any startup errors can be caught and properly logged. The problem is that now we're in a chicken-and-egg situation: we want to setup the logger early, but we need the TelemetryConfiguration which still haven't been added to our DI container.

Luckily from version 4.0.x of the Serilog.Extensions.Hosting we have the possibility to configure a bootstrap logger to capture early errors, and then change it using DI-dependent services once they are configured.

// dotnet add package Serilog.Extensions.Hosting

public static class Program
{
    public static void Main(string[] args)
    {
        Log.Logger = new LoggerConfiguration()
            .WriteTo.Console()
            .CreateBootstrapLogger();

        try
        {
            CreateHostBuilder(args).Build().Run();
        }
        catch (Exception ex)
        {
            Log.Fatal(ex, "An unhandled exception occurred during bootstrapping");
        }
        finally
        {
            Log.CloseAndFlush();
        }
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .UseSerilog((context, services, loggerConfiguration) => loggerConfiguration
                .WriteTo.ApplicationInsights(
                    services.GetRequiredService<TelemetryConfiguration>(),
                    TelemetryConverter.Traces))
            .ConfigureWebHostDefaults(webBuilder => { webBuilder.UseStartup<Startup>(); });
}

Configuring with ReadFrom.Configuration()

Configuring in code, as shown above, is recommended because the existing TelemetryClient can be injected.

The following configuration shows how to create an ApplicationInsights sink with ReadFrom.Configuration(configuration).

{
  "Serilog": {
    "Using": [
      "Serilog.Sinks.ApplicationInsights"
    ],
    "MinimumLevel": {
      "Default": "Information",
      "Override": {
        "Microsoft": "Warning",
        "System": "Warning"
      }
    },
    "WriteTo": [
      {
        "Name": "ApplicationInsights",
        "Args": {
          "connectionString": "[your connection string here]",
          "telemetryConverter":
                        "Serilog.Sinks.ApplicationInsights.TelemetryConverters.TraceTelemetryConverter, Serilog.Sinks.ApplicationInsights"
        }
      }
    ],
    "Enrich": [ "FromLogContext" ],
    "Properties": {
      "Application": "Sample"
    }
  }
}

The telemetryConverter has to be specified with the full type name and the assembly name.

A connectionString can be omitted if it's supplied in the APPLICATIONINSIGHTS_CONNECTION_STRING environment variable.

What does the sink submit?

By default, trace telemetry submits:

• rendered message in trace's standard message property.
• severity in trace's standard severityLevel property.
• timestamp in trace's standard timestamp property.
• operation id from OperationId property, or the LogEvent.TraceId property.
• operation parent id from ParentSpanId property.
• operation name from OperationName property.
• component version from Version property.
• messageTemplate in customDimensions.
• custom log properties as customDimensions.

Event telemetry submits:

• message template as event name.
• renderedMessage in customDimensions.
• timestamp in event's standard timestamp property.
• operation id from OperationId property, or the LogEvent.TraceId property.
• operation parent id from ParentSpanId property.
• operation name from OperationName property.
• component version from Version property.
• custom log properties as customDimensions.

Exception telemetry submits:

• exception as standard AI exception.
• severity in trace's standard severityLevel property.
• timestamp in trace's standard timestamp property.
• operation id from OperationId property, or the LogEvent.TraceId property.
• operation parent id from ParentSpanId property.
• operation name from OperationName property.
• component version from Version property.
• custom log properties as customDimensions.

Note that log context properties are also included in customDimensions when Serilog is configured with .Enrich.FromLogContext().

How custom properties are logged?

By default custom properties are converted to compact JSON, for instance:

var position = new { Latitude = 25, Longitude = 134 };
var elapsedMs = 34;
var numbers = new int[] { 1, 2, 3, 4 };

Logger.Information("Processed {@Position} in {Elapsed:000} ms., str {str}, numbers: {numbers}",
    position, elapsedMs, "test", numbers);

will produce the following properties in customDimensions:

Property	Value
Elapsed	34
Position	{"Latitude":25,"Longitude":134}
numbers	[1,2,3,4]

This is a breaking change from v2 which was producing these properties:

Property	Value
Elapsed	34
Position.Latitude	25
Position.Longitude	134
numbers.0	1
numbers.1	2
numbers.2	3
numbers.3	4

You can revert the old behavior by overriding standard telemetry formatter, for instance:

private class DottedOutTraceTelemetryConverter : TraceTelemetryConverter
{
    public override IValueFormatter ValueFormatter => new ApplicationInsightsDottedValueFormatter();
}

Customizing

Additionally, you can also customize whether to send the LogEvents at all, if so which type(s) of Telemetry to send and also what to send (all or no LogEvent properties at all) by passing your own ITelemetryConverter instead of TelemetryConverter.Traces or TelemetryConverter.Events by either implementing your own ITelemetryConverter or deriving from TraceTelemetryConverter or EventTelemetryConverter and overriding specific bits.

Log.Logger = new LoggerConfiguration()
    .WriteTo.ApplicationInsights(configuration, new CustomConverter())
    .CreateLogger();
// ...

private class CustomConverter : TraceTelemetryConverter
{
    public override IEnumerable<ITelemetry> Convert(LogEvent logEvent, IFormatProvider formatProvider)
    {
        // first create a default TraceTelemetry using the sink's default logic
        // .. but without the log level, and (rendered) message (template) included in the Properties
        foreach (ITelemetry telemetry in base.Convert(logEvent, formatProvider))
        {
            // then go ahead and post-process the telemetry's context to contain the user id as desired
            if (logEvent.Properties.ContainsKey("UserId"))
            {
                telemetry.Context.User.Id = logEvent.Properties["UserId"].ToString();
            }
            // post-process the telemetry's context to contain the operation id
            if (logEvent.Properties.ContainsKey("OperationId"))
            {
                telemetry.Context.Operation.Id = logEvent.Properties["OperationId"].ToString();
            }
            // post-process the telemetry's context to contain the operation parent id
            if (logEvent.Properties.ContainsKey("ParentSpanId"))
            {
                telemetry.Context.Operation.ParentId = logEvent.Properties["ParentSpanId"].ToString();
            }
            // typecast to ISupportProperties so you can manipulate the properties as desired
            ISupportProperties propTelemetry = (ISupportProperties)telemetry;

            // find redundant properties
            var removeProps = new[] { "UserId", "ParentSpanId", "OperationId" };
            removeProps = removeProps.Where(prop => propTelemetry.Properties.ContainsKey(prop)).ToArray();

            foreach (var prop in removeProps)
            {
                // remove redundant properties
                propTelemetry.Properties.Remove(prop);
            }

            yield return telemetry;
        }
    }
}

If you want to skip sending a particular LogEvent, just return null from your own converter method.

Customising included properties

The easiest way to customise included properties is to subclass one of the ITelemetryConverter implementations. For instance, let's include renderedMessage in event telemetry:

private class IncludeRenderedMessageConverter : EventTelemetryConverter
{
    public override void ForwardPropertiesToTelemetryProperties(LogEvent logEvent,
        ISupportProperties telemetryProperties, IFormatProvider formatProvider)
    {
        base.ForwardPropertiesToTelemetryProperties(logEvent, telemetryProperties, formatProvider,
            includeLogLevel: false,
            includeRenderedMessage: true,
            includeMessageTemplate: false);
    }
}

How, When and Why to Flush Messages Manually

Or: Where did my Messages go?

As explained by the Application Insights documentation , the default behaviour of the AI client is to buffer messages and send them to AI in batches whenever the client seems fit. However, this may lead to lost messages when your application terminates while there are still unsent messages in said buffer.

You can control when AI shall flush its messages, for example when your application closes:

1. Create a custom TelemetryClient and hold on to it in a field or property:

// private TelemetryClient _telemetryClient;

// ...
var telemetryConfiguration = TelemetryConfiguration.CreateDefault();
telemetryConfiguration.ConnectionString = "<your Application Insights connection string>";

_telemetryClient = new TelemetryClient(telemetryConfiguration);

2. Use that custom TelemetryClient to initialize the Sink:

var log = new LoggerConfiguration()
    .WriteTo.ApplicationInsights(_telemetryClient, TelemetryConverter.Events)
    .CreateLogger();

3. Call .Flush() on the TelemetryClient whenever you deem necessary, i.e. Application Shutdown:

_telemetryClient.Flush();

// The AI documentation mentions that calling `Flush()` *can* be asynchronous and non-blocking so
// depending on the underlying Channel to AI you might want to wait some time
// specific to your application and its connectivity constraints for the flush to finish.

await Task.Delay(1000);

// or

System.Threading.Thread.Sleep(1000);

Including Operation Id

Application Insight's operation id is set from the following sources in order of precedence:

1. OperationId LogEvent property
2. TraceId LogEvent property

This can be set like so:

public class OperationIdEnricher : ILogEventEnricher
{
    public void Enrich(LogEvent logEvent, ILogEventPropertyFactory propertyFactory)
    {
        if (logEvent.Properties.TryGetValue("RequestId", out var requestId))
        {
            logEvent.AddPropertyIfAbsent(new LogEventProperty("OperationId", requestId));
        }
    }
}

Including Version

Application Insight supports component version and is pushed out if you set Version log event property. If it's present, AI's operation version will include the value from this property.

Using with SerilogTracing

SerilogTracing provides tracing primitives that integrate with Serilog's structured logging. When used with this sink, tracing context is automatically included in Application Insights telemetry.

The following LogEvent properties are mapped to Application Insights telemetry:

LogEvent Property	Application Insights Telemetry	Notes
TraceId	Context.Operation.Id	From TraceId captured in LogEvent
SpanId	Id (for Request/Dependency telemetry)	From SpanId captured in LogEvent
ParentSpanId	Context.Operation.ParentId
OperationName	Context.Operation.Name
OperationId	Context.Operation.Id	Overrides TraceId
Version	Context.Component.Version

If present, Baggage is forwarded to Application Insights custom dimensions (telemetry.Properties).

Precedence for Context.Operation.Id: OperationId property > TraceId property (when both OperationId and TraceId properties are absent).

Enriching from Activity (explicit opt-in)

This sink is designed to work well with Serilog's asynchronous/batched processing. To keep telemetry deterministic, adding OperationName and Baggage from the ambient Activity is an explicit opt-in: copy the values onto the LogEvent before it reaches the sink.

The sink includes an enricher that adds this by default. Enable it using the provided Enrich extension method:

Log.Logger = new LoggerConfiguration()
    .Enrich.WithActivityDetails(includeOperationName: true, includeBaggage: true)
    .WriteTo.ApplicationInsights(telemetryConfiguration, TelemetryConverter.Traces)
    .CreateLogger();

Upgrading to 5.0 (from 4.x)

This is a new major release (5.0). Notable changes:

• OperationName and Baggage are opt-in: they are only forwarded when present as LogEvent properties (use the built-in enricher above or your own enricher).
• Less redundancy in custom dimensions by default: operation-related values are set on ITelemetry.Context and are not duplicated into telemetry.Properties unless enabled.

TelemetryConverterBase constructor flags

Converters derived from TelemetryConverterBase can be configured to also include selected operation-related values in telemetry.Properties (custom dimensions):

public TelemetryConverterBase(
    bool includeOperationIdPropertyAsTelemetryProperty,
    bool includeParentSpanIdPropertyAsTelemetryProperty,
    bool includeOperationNamePropertyAsTelemetryProperty,
    bool includeVersionPropertyAsTelemetryProperty)

If you previously relied on these values being present in telemetry.Properties, enable the relevant flags when constructing your converter, or post-process telemetry in a custom converter.

Using with Azure Functions

Azure functions has out of the box integration with Application Insights, which automatically logs functions execution start, end, and any exception. Please refer to the original documentation on how to enable it.

This sink can enrich AI messages, preserving operation_Id and other context information which is already provided by functions runtime. The easiest way to configure Serilog in this case is to use the injected TelemetryClient which should be automatically configured by the environment through the APPLICATIONINSIGHTS_CONNECTION_STRING appsetting. You can, for instance, initialise logging in the static constructor:

[assembly: FunctionsStartup(typeof(MyFunctions.Startup))]
namespace MyFunctions
{
    public class Startup : FunctionsStartup
    {
        public override void Configure(IFunctionsHostBuilder builder)
        {
            builder.Services.AddSingleton<ILoggerProvider>((sp) =>
            {
                Log.Logger = new LoggerConfiguration()
                    .Enrich.FromLogContext()
                    .WriteTo.ApplicationInsights(sp.GetRequiredService<TelemetryClient>(), TelemetryConverter.Traces)
                    .CreateLogger();
                return new SerilogLoggerProvider(Log.Logger, true);
            });
        }
    }
}

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See also: Serilog Documentation