Register internal ResourceMonitor with ResourceUtilizationHealthCheck

[evgenyfedorov2]

Fixes #4560

What is changing

ResourceUtilizationHealthCheck depends on IResourceMonitor and requires an implementation of it to be registered first, which is also mentioned in #4560. Typically, users would achieve this by calling the AddResourceMonitoring() method which registers the internal ResourceMonitorService for this purpose:

var serviceCollection = new ServiceCollection();
serviceCollection.AddResourceMonitoring();
serviceCollection.AddResourceUtilizationHealthCheck();

After this change, users don't have to call AddResourceMonitoring() and can just call AddResourceUtilizationHealthCheck() immediately:

var serviceCollection = new ServiceCollection();
serviceCollection.AddResourceUtilizationHealthCheck();

Impact

• If you use AddResourceMonitoring() method call, you may omit it.

• If you use a custom implementation of IResourceMonitor and register it using the AddSingleton<IResourceMonitor, TImplementation>() method, then no action is required.

• If you use a custom implementation of IResourceMonitor and register it using the TryAddSingleton<IResourceMonitor, TImplementation>() method which is placed before AddResourceUtilizationHealthCheck(), then no action is required. For example, assuming the custom implementation TImplementation class name is MyResourceMonitorService, the following scenarios will continue to work as is:

  ✅ works:

   // 1.
   var serviceCollection = new ServiceCollection();
   serviceCollection.AddSingleton<IResourceMonitor, MyResourceMonitorService>();
   serviceCollection.AddResourceUtilizationHealthCheck();
  

  ✅ works:

  // 2.
  var serviceCollection = new ServiceCollection();
  serviceCollection.AddResourceUtilizationHealthCheck();
  serviceCollection.AddSingleton<IResourceMonitor, MyResourceMonitorService>();
  

  ✅ works:

  // 3.
  var serviceCollection = new ServiceCollection();
  serviceCollection.TryAddSingleton<IResourceMonitor, MyResourceMonitorService>();
  serviceCollection.AddResourceUtilizationHealthCheck();
  

• If you use TryAddSingleton<IResourceMonitor, TImplementation>() which is placed after the AddResourceUtilizationHealthCheck() method call, then the following will not work, because the internal ResourceMonitorService will be registered and used instead of the MyResourceMonitorService:

  ❌ does not work:

   // 4.
   var serviceCollection = new ServiceCollection();
   serviceCollection.AddResourceUtilizationHealthCheck();
   serviceCollection.TryAddSingleton<IResourceMonitor, MyResourceMonitorService>();
  

  To fix that, please use either AddSingleton<IResourceMonitor, TImplementation>() extension methods, or place the registration before the AddResourceUtilizationHealthCheck() method call:

  ✅ works:

   // 5.
   var serviceCollection = new ServiceCollection();
   serviceCollection.TryAddSingleton<IResourceMonitor, MyResourceMonitorService>();
   serviceCollection.AddResourceUtilizationHealthCheck();
  

Microsoft Reviewers: Open in CodeFlow

[RussKie]

• This change breaks customers who use TryAddSingleton<IResourceMonitor>() only when it is placed after the AddResourceUtilizationHealthCheck() method call. I don't think there is a way to avoid this.

How can we help customers to detect and avoid this?
What will be the experience if customers do have the "incorrect" code? Will they be getting meaningful error messages?
What kind of documentation and primers do we need for this?

[evgenyfedorov2]

• This change breaks customers who use TryAddSingleton<IResourceMonitor>() only when it is placed after the AddResourceUtilizationHealthCheck() method call. I don't think there is a way to avoid this.

How can we help customers to detect and avoid this?

We will update our documentation at https://learn.microsoft.com/en-us/dotnet/core/diagnostics/diagnostic-health-checks

What will be the experience if customers do have the "incorrect" code? Will they be getting meaningful error messages?

The library will silently use the built-in ResourceMonitoringService instead of the custom one provided by customers. Also, I don't see any way to avoid this because we cannot hook into the IServiceProvider right before the build started and check if a custom implementation was registered or not.

What kind of documentation and primers do we need for this?

Update the docs as mentioned above. Add a note about the order of registration.

[RussKie]

Please link the pull-request updating the docs here as well.

[evgenyfedorov2]

Please link the pull-request updating the docs here as well.

dotnet/docs#42626