OpenTelemetry logging to console in JSON format

Question

Hello I need to have OpenTelemetry logs/metrics/traces sent to console of my application, but in JSON fromat. It's a .NET 8 ASP.NET application set up loosely following: https://learn.microsoft.com/en-us/dotnet/core/diagnostics/observability-with-otel, the application already Microsoft logger with JSON log formatter (see below, uses a custom JsonLogFormatter class). The problem is that all logs are actually formatted as JSON, but the OpenTelemetry is not.

        var builder = WebApplication.CreateBuilder(args);
        var services = builder.Services;

        // OpenTelemetry stuff...
        var otel = services.AddOpenTelemetry();
        otel.WithMetrics(metrics => metrics
            .AddAspNetCoreInstrumentation()
            .AddMeter("Microsoft.AspNetCore.Hosting")
            .AddMeter("Microsoft.AspNetCore.Server.Kestrel")
        );
        otel.WithTracing(tracing =>
        {
            tracing.AddAspNetCoreInstrumentation();
            tracing.AddHttpClientInstrumentation();
            tracing.AddConsoleExporter();
        });
        [...]
        // JSON Microsoft logger added like so...
        var loggerFactory = LoggerFactory.Create(builder =>
        {
            builder.ClearProviders();
            builder.AddConfiguration(configuration.GetSection("Logging"))
                .AddConsole();
            builder.AddConsoleFormatter<JsonLogFormatter, JsonLogOptions>();
        });
        services.AddSingleton(loggerFactory);
        services.AddLogging();

Console output:

{"message":"Hosting starting","machineName":"XXX","source":"Microsoft.Extensions.Hosting.Internal.Host","level":"Debug","timestamp":"2024-03-14T19:38:23.2569003+01:00"}
Activity.TraceId:            8794488a000a8aa943fb4bd76b8becbe
Activity.SpanId:             bae785686698f263
Activity.TraceFlags:         Recorded
Activity.ActivitySourceName: System.Net.Http
Activity.DisplayName:        GET
Activity.Kind:               Client
[..]
{"message":"Now listening on: https://localhost:6001","...}

I would truly like to have OpenTelemetry as JSON in this log example. :)

Answer 1

Currently, this is not supported by OpenTelemetry .NET. You will either need to create a new exporter or customize the existing ConsoleExporter.

Here is the code to look at: https://github.com/open-telemetry/opentelemetry-dotnet/tree/main/src/OpenTelemetry.Exporter.Console

Also, be sure to leave a comment that this is something you'd like to see included in the library. There is already an open issue: https://github.com/open-telemetry/opentelemetry-dotnet/issues/5036