Service discovery in .NET

In this article, you learn how to use the Microsoft.Extensions.ServiceDiscovery library. Service discovery is a way for developers to use logical names instead of physical addresses (IP address and port) to refer to external services.

Get Started

To get started with service discovery in .NET, install the Microsoft.Extensions.ServiceDiscovery NuGet package.

dotnet add package Microsoft.Extensions.ServiceDiscovery --prerelease

For more information, see dotnet add package or Manage package dependencies in .NET applications.

Example usage

In the Program.cs file of your project, call the AddServiceDiscovery extension method to add service discovery to the host, configuring default service endpoint resolvers:

builder.Services.AddServiceDiscovery();

Add service discovery to an individual IHttpClientBuilder by calling the AddServiceDiscovery extension method:

builder.Services.AddHttpClient<CatalogServiceClient>(static client =>
    {
        client.BaseAddress = new("https://catalog");
    })
    .AddServiceDiscovery();

Alternatively, you can add service discovery to all HttpClient instances by default:

builder.Services.ConfigureHttpClientDefaults(static http =>
{
    // Turn on service discovery by default
    http.AddServiceDiscovery();
});

Scheme selection when resolving HTTP(S) endpoints

It is common to use HTTP while developing and testing a service locally and HTTPS when the service is deployed. Service Discovery supports this by allowing for a priority list of URI schemes to be specified in the input string given to Service Discovery. Service Discovery will attempt to resolve the services for the schemes in order and will stop after an endpoint is found. URI schemes are separated by a + character, for example: "https+http://basket". Service Discovery will first try to find HTTPS endpoints for the "basket" service and will then fall back to HTTP endpoints. If any HTTPS endpoint is found, Service Discovery will not include HTTP endpoints.

Schemes can be filtered by configuring the AllowedSchemes and AllowAllSchemes properties on ServiceDiscoveryOptions. The AllowAllSchemes property is used to indicate that all schemes are allowed. By default, AllowAllSchemes is true and all schemes are allowed. Schemes can be restricted by setting AllowAllSchemes to false and adding allowed schemes to the AllowedSchemes property. For example, to allow only HTTPS:

services.Configure<ServiceDiscoveryOptions>(options =>
{
    options.AllowAllSchemes = false;
    options.AllowedSchemes = ["https"];
});

To explicitly allow all schemes, set the ServiceDiscoveryOptions.AllowAllSchemes property to true:

services.Configure<ServiceDiscoveryOptions>(
    options => options.AllowAllSchemes = true);

Resolve service endpoints from configuration

The AddServiceDiscovery extension method adds a configuration-based endpoint resolver by default. This resolver reads endpoints from the .NET configuration system. The library supports configuration through appsettings.json, environment variables, or any other IConfiguration source.

Here's an example demonstrating how to configure endpoints for the service named catalog via appsettings.json:

{
  "Services": {
    "catalog": {
      "https": [
        "localhost:8080",
        "10.46.24.90:80"
      ]
    }
  }
}

The preceding example adds two endpoints for the service named catalog: https://localhost:8080, and "https://10.46.24.90:80". Each time the catalog is resolved, one of these endpoints is selected.

If service discovery was added to the host using the AddServiceDiscoveryCore extension method on IServiceCollection, the configuration-based endpoint resolver can be added by calling the AddConfigurationServiceEndPointResolver extension method on IServiceCollection.

Configuration

The configuration resolver is configured using the ConfigurationServiceEndPointResolverOptions class, which offers these configuration options:

  • SectionName: The name of the configuration section that contains service endpoints. It defaults to "Services".

  • ApplyHostNameMetadata: A delegate used to determine if host name metadata should be applied to resolved endpoints. It defaults to a function that returns false.

To configure these options, you can use the Configure extension method on the IServiceCollection within your application's Startup class or Program file:

var builder = WebApplication.CreateBuilder(args);

builder.Services.Configure<ConfigurationServiceEndPointResolverOptions>(
    static options =>
    {
        options.SectionName = "MyServiceEndpoints";
    
        // Configure the logic for applying host name metadata
        options.ApplyHostNameMetadata = static endpoint =>
        {
            // Your custom logic here. For example:
            return endpoint.EndPoint is DnsEndPoint dnsEp
                && dnsEp.Host.StartsWith("internal");
        };
    });

The preceding example demonstrates setting a custom section name for your service endpoints and providing custom conditional logic for applying host name metadata.

Resolve service endpoints using platform-provided service discovery

Certain platforms, like Azure Container Apps and Kubernetes (when configured accordingly), offer service discovery capabilities without necessitating a service discovery client library. In cases where an application is deployed in such environments, using the platform's built-in functionality can be advantageous. The pass-through resolver is designed to facilitate this scenario. It enables the utilization of alternative resolvers, such as configuration, in different environments, such as a developer's machine. Importantly, this flexibility is achieved without the need for any code modifications or the implementation of conditional guards.

The pass-through resolver performs no external resolution and instead resolves endpoints by returning the input service name represented as a DnsEndPoint.

The pass-through provider is configured by-default when adding service discovery via the AddServiceDiscovery extension method.

If service discovery was added to the host using the AddServiceDiscoveryCore extension method on IServiceCollection, the pass-through provider can be added by calling the AddPassThroughServiceEndPointResolver extension method on IServiceCollection.

See also