Networking event counters in .NET

Article
11/30/2023

EventCounters are .NET APIs used for lightweight, cross-platform, and near real-time performance metric collection.

Networking components are instrumented to publish basic diagnostic information using EventCounters. They include information like the following:

System.Net.Http > requests-started
System.Net.Http > requests-failed
System.Net.Http > http11-connections-current-total
System.Net.Security > all-tls-sessions-open
System.Net.Sockets > outgoing-connections-established
System.Net.NameResolution > dns-lookups-duration

Tip

For the full list, see well-known counters.

Tip

On projects targeting .NET 8+, consider using the newer and more feature-rich networking metrics instead of EventCounters.

Providers

Networking information is split across the following providers:

System.Net.Http (HttpClient and SocketsHttpHandler)
System.Net.NameResolution (Dns)
System.Net.Security (SslStream)
System.Net.Sockets
Microsoft.AspNetCore.Hosting
Microsoft-AspNetCore-Server-Kestrel

The telemetry has some performance overhead when enabled, so make sure to subscribe only to providers you're actually interested in.

Monitor event counters from outside the process

dotnet-counters

dotnet-counters is a cross-platform performance monitoring tool for ad-hoc health monitoring and first-level performance investigation.

dotnet tool install --global dotnet-counters

dotnet-counters monitor --counters System.Net.Http,System.Net.Security --process-id 1234

The command continually refreshes the console with the latest numbers.

[System.Net.Http]
    Current Http 1.1 Connections                       3
    Current Http 2.0 Connections                       1
    Current Http 3.0 Connections                       0
    Current Requests                                   4
    HTTP 1.1 Requests Queue Duration (ms)              0
    HTTP 2.0 Requests Queue Duration (ms)              0
    HTTP 3.0 Requests Queue Duration (ms)              0
    Requests Failed                                    0
    Requests Failed Rate (Count / 1 sec)               0
    Requests Started                                 470
    Requests Started Rate (Count / 1 sec)             18

For all the available commands and parameters, see the dotnet-counter docs.

Application Insights

Application Insights does not collect event counters by default. For information on customizing the set of counters you're interested in, see the AppInsights EventCounters docs.

For example:

services.ConfigureTelemetryModule<EventCounterCollectionModule>((module, options) =>
{
    module.Counters.Add(new EventCounterCollectionRequest("System.Net.Http", "current-requests"));
    module.Counters.Add(new EventCounterCollectionRequest("System.Net.Http", "requests-failed"));
    module.Counters.Add(new EventCounterCollectionRequest("System.Net.Http", "http11-connections-current-total"));
    module.Counters.Add(new EventCounterCollectionRequest("System.Net.Security", "all-tls-sessions-open"));
});

For an example of how to subscribe to many runtime and ASP.NET event counters, see the RuntimeEventCounters sample. Simply add an EventCounterCollectionRequest for every entry.

foreach (var (eventSource, counters) in RuntimeEventCounters.EventCounters)
{
    foreach (string counter in counters)
    {
        module.Counters.Add(new EventCounterCollectionRequest(eventSource, counter));
    }
}

Consume event counters in-process

The Yarp.Telemetry.Consumption library makes it easy to consume event counters from within the process. While the package is currently maintained as part of the YARP project, it can be used in any .NET application.

To use it, implement the IMetricsConsumer<TMetrics> interface:

public sealed class MyMetricsConsumer : IMetricsConsumer<SocketsMetrics>
{
    public void OnMetrics(SocketsMetrics previous, SocketsMetrics current)
    {
        var elapsedTime = (current.Timestamp - previous.Timestamp).TotalMilliseconds;
        Console.WriteLine($"Received {current.BytesReceived - previous.BytesReceived} bytes in the last {elapsedTime:N2} ms");
    }
}

Then register the implementations with your DI container:

services.AddSingleton<IMetricsConsumer<SocketsMetrics>, MyMetricsConsumer>();
services.AddTelemetryListeners();

The library provides the following strongly typed metrics types:

Need more telemetry?

If you have suggestions for other useful information that could be exposed via events or metrics, create a dotnet/runtime issue.

If you're using the Yarp.Telemetry.Consumption library and have any suggestions, create a microsoft/reverse-proxy issue.

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