metrics.md

Metrics

Metrics are reported in the Prometheus wire format. Under the hood, we're using the excellent prometheus-net client for .NET.

To add a Prometheus metrics scraping endpoint, register the HTTP handler like so:

<location path="metrics">
    <system.webServer>
        <handlers>
            <add name="ToolhouseMetricsHandler" path="*" verb="*" type="Toolhouse.Monitoring.MetricsEndpointHandler, Toolhouse.Monitoring"/>
        </handlers>
    </system.webServer>
</location>

To automatically generate metrics around incoming HTTP requests and application exceptions, add Toolhouse.Monitoring.Modules.MetricsModule to your Web.config:

<system.webServer>
    <modules runAllManagedModulesForAllRequests="true">
        <add name="ToolhouseMetricsModule" type="Toolhouse.Monitoring.Modules.MetricsModule, Toolhouse.Monitoring"/>
    </modules>
</system.webServer>

Standard Metrics

Out of the box, the metrics module provides the following metrics:

Metric	Type	Description
http_requests_total	counter	Increments for each incoming request received.
http_responses_total	counter	Increments for each response returned, with status label for HTTP status.
http_current_requests	gauge	Number of requests currently being handled.
http_request_duration_seconds	histogram	Amount of time requests take to process.
errors_total	counter	Increments for each uncaught exception, with error label for Exception type (i.e. System.Exception).

Note that all metrics are automatically given a backend label set to Environment.MachineName.

Additional Metrics

The Toolhouse.Monitoring.Metrics class defines some static methods for working with other kinds of metrics, including:

• IncrementEmailsSent(string) - For tracking emails sent.
• InstrumentApiCall(string, Func<bool>) - For instrumenting calls to 3rd party APIs.