Provide a way to differentiate HttpClient configuration

The newly added IHttpClientFactory integration only exposes HTTP request host and method as labels. While a good start, this is not enough to really identify which (out of several possible) HttpClient configurations/types the metric applies to.

Ideally, we could track the “foo” in services.AddHttpClient("foo", ...) but I did not find any way to get access to this information in our middleware.

Ref: https://github.com/dotnet/aspnetcore/discussions/27018 Ref #248, #229 Ref https://github.com/dotnet/aspnetcore/issues/28455

[ricardopaiva]

The solution I’ve implemented was to create a delegate handler, create the Counter inside it and register that handler in the http client. That way, the counter will be automatically called whenever the http client is used and there’s no need to repeat this code all over the solution.

Here’s my DelegateHandler:

using Microsoft.AspNetCore.Http;
using Prometheus;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Net.Http;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace <namespace>
{
    public class HttpClientMetricsHandler : DelegatingHandler
    {
        private readonly IHttpContextAccessor _accessor;

        private static readonly Counter HttpRequestsCount = Metrics
            .CreateCounter("integrationapi_http_requests_to_external_api_total", "Number of http requests to external API.",
                new CounterConfiguration
                {
                    LabelNames = new[] { "method", "endpoint" }
                });

        public HttpClientMetricsHandler(IHttpContextAccessor accessor)
        {
            _accessor = accessor;
        }

        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request,
            CancellationToken cancellationToken)
        {
            var context = _accessor.HttpContext;
            HttpRequestsCount.WithLabels(context.Request.Method, context.Request.Path).Inc();
            var response = await base.SendAsync(request, cancellationToken);
            return response;
        }
    }
}

And in my Service I’m register this handler like this:

services.AddTransient<HttpClientMetricsHandler>();

services.AddHttpClient("<my http client name>", client =>
{
    client.BaseAddress = new Uri(configuration["ApiConfig:BaseUrl"]);
    client.DefaultRequestHeaders.Add("Accept", "application/json");
})
    .AddHttpMessageHandler<HttpClientMetricsHandler>()
    .UseHttpClientMetrics();

[ricardopaiva]

It’s working perfectly fine without the IHttpContextAccessor for me. Microsoft uses AddTransient in their example, so I’ll stick with that.

Sorry, I misread your post. I thought you’re still having problems. In my case I only want to know how many calls are being made by the HttpClient. At least for now, I don’t need to know the endpoint so I can exclude that so that I don’t have that problem with high label cardinality.