Always include request GUID/Correlation Id in IIS 7+ logs

Question

We need to watch requests/failures through response to the client. We've determined that using a uniquely generated correlation id is best.

As an entry point to one or more API's, our .NET Web API 2 application receives requests via IIS 7+. To track a request (whether it failed OR succeeded), we need for the IIS log files to include unique GUID (assuming an ActivityID). We know once we are within the Web API, we can gather the ActivityId from CorrelationManager.ActivityId but at the host/server level, we need this to be reported.

... For all requests, successful or failed, how do we get IIS to start with including its own unique correlation identifier in logs it touches?

Answer 1

In IIS, you can add custom logging fields based on request headers, response headers and server variables. So, one option is to add the ActivityId to the response headers, as described here.

For ASP MVC and SerilogWeb.Classic, add this to Global.asax.cs:

protected void Application_EndRequest(object sender, EventArgs e)
{
    if (sender is HttpApplication application)
    {
        var httpResponse = application.Context.Response;

        if (httpResponse.HeadersWritten)
        {
            return;
        }

        // Fetch correlation ID used by Serilog and add onto response header, so that IIS can include it in IIS request log
        if (httpResponse.Headers["X-Correlation-Id"] == null && HttpRequestIdEnricher.TryGetCurrentHttpRequestId(out var correlationId))
        {
            httpResponse.Headers.Add("X-Correlation-Id", correlationId.ToString());
        }
    }
}

However, you would replace correlationId with your ActivityId.

Then, set up IIS logging like so: