Destination response time metrics

[shawntoffel]

Hello,

I want to add metrics/logs for the response time of the destination endpoint. In other words, the time from proxy -> destination -> proxy excluding any Yarp related middleware. I've created an approach based on the Metrics sample. Is this a valid way to accomplish this? Is there a better way? Ideally, I can also log the destinationId and path (I can get path from HttpContext).

Thank you.

public class HttpRequestMetrics
{
    private static readonly AsyncLocal<HttpRequestMetrics> Local = new();
    public static HttpRequestMetrics Current => Local.Value ??= new HttpRequestMetrics();

    public DateTime StartTime { get; set; }
    public DateTime StopTime { get; set; }

    public TimeSpan ElapsedTime => StopTime - StartTime;
}

public class HttpClientTelemetryConsumer : IHttpTelemetryConsumer
{
    public void OnRequestStart(DateTime timestamp, string scheme, string host, int port, string pathAndQuery, int versionMajor, int versionMinor, HttpVersionPolicy versionPolicy) 
        => HttpRequestMetrics.Current.StartTime = timestamp;

    public void OnRequestStop(DateTime timestamp)
        => HttpRequestMetrics.Current.StopTime = timestamp;
}

public class PerRequestYarpMetricCollectionMiddleware
{
    private readonly RequestDelegate _next;
    private readonly ILogger<PerRequestYarpMetricCollectionMiddleware> _logger;

    public PerRequestYarpMetricCollectionMiddleware(RequestDelegate next, ILogger<PerRequestYarpMetricCollectionMiddleware> logger)
    {
        _logger = logger;
        _next = next;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        var metrics = HttpRequestMetrics.Current;
        await _next(context);
        _logger.LogInformation($"Request to {context.Request.Path} took {metrics.ElapsedTime.Milliseconds}ms");
    }
}

[MihaZupan]

Yes, this looks okay.

Depending on what exactly it is you are interested in, you can tweak when you collect the start/stop timestamps.

For example:

• OnRequestStart/OnRequestStop will include any time taken to establish a new connection to the destination (including TLS handshake)
• OnRequestHeadersStop/OnResponseHeadersStop would be the closest to how long it took the proxy to receive the response headers after sending the request out

[shawntoffel]

This is good information. Thank you!