opentelemetry-dotnet/docs/metrics/customizing-the-sdk/README.md

Customizing OpenTelemetry .NET SDK for Metrics

MeterProvider

As shown in the getting-started doc, a valid MeterProvider must be configured and built to collect metrics with OpenTelemetry .NET Sdk. MeterProvider holds all the configuration for metrics like MetricReaders, Views, etc. Naturally, almost all the customizations must be done on the MeterProvider.

Building a MeterProvider

Building a MeterProvider is done using MeterProviderBuilder which must be obtained by calling Sdk.CreateMeterProviderBuilder(). MeterProviderBuilder exposes various methods which configure the provider it is going to build. These include methods like AddMeter, AddView etc, and are explained in subsequent sections of this document. Once configuration is done, calling Build() on the MeterProviderBuilder builds the MeterProvider instance. Once built, changes to its configuration is not allowed. In most cases, a single MeterProvider is created at the application startup, and is disposed when application shuts down.

The snippet below shows how to build a basic MeterProvider. This will create a provider with default configuration, and is not particularly useful. The subsequent sections show how to build a more useful provider.

using OpenTelemetry;
using OpenTelemetry.Metrics;

using var meterProvider = Sdk.CreateMeterProviderBuilder().Build();

MeterProvider configuration

MeterProvider holds the metrics configuration, which includes the following:

1. The list of Meters from which instruments are created to report measurements.
2. The list of instrumentations enabled via Instrumentation Library.
3. The list of MetricReaders, including exporting readers which exports metrics to Exporters
4. The Resource associated with the metrics.
5. The list of Views to be used.

Meter

Meter is used for creating Instruments, which are then used to report Measurements. The SDK follows an explicit opt-in model for listening to meters. i.e, by default, it listens to no meters. Every meter which is used to create instruments must be explicitly added to the meter provider.

AddMeter method on MeterProviderBuilder can be used to add a Meter to the provider. The name of the Meter (case-insensitive) must be provided as an argument to this method. AddMeter can be called multiple times to add more than one meters. It also supports wild-card subscription model.

It is not possible to add meters once the provider is built by the Build() method on the MeterProviderBuilder.

The snippet below shows how to add meters to the provider.

using OpenTelemetry;
using OpenTelemetry.Metrics;

using var meterProvider = Sdk.CreateMeterProviderBuilder()
    // The following enables instruments from Meter
    // named "MyCompany.MyProduct.MyLibrary" only.
    .AddMeter("MyCompany.MyProduct.MyLibrary")
    // The following enables instruments from all Meters
    // whose name starts with  "AbcCompany.XyzProduct.".
    .AddMeter("AbcCompany.XyzProduct.*")
    .Build();

See Program.cs for complete example.

Note: A common mistake while configuring MeterProvider is forgetting to add the required Meters to the provider. It is recommended to leverage the wildcard subscription model where it makes sense. For example, if your application is expecting to enable instruments from a number of libraries from a company "Abc", the you can use AddMeter("Abc.*") to enable all meters whose name starts with "Abc.".

View

// TODO

Instrumentation

// TODO

MetricReader

// TODO

Resource

// TODO