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title	author	description	monikerRange	ms.author	ms.date	uid
Migrating gRPC services from C-core to ASP.NET Core	juntaoluo	Learn how to move an existing C-core based gRPC app to run on top of ASP.NET Core stack.	>= aspnetcore-3.0	johluo	03/08/2019	grpc/migration

Migrating gRPC services from C-core to ASP.NET Core

By John Luo

Due to implementation of the underlying stack, not all features work in the same way between C-core based gRPC apps and ASP.NET Core based apps. This document highlights the key differences to note when migrating between the two stacks.

gRPC service implementation lifetime

In the ASP.NET Core stack, gRPC services, by default, will be created with a Scoped lifetime. In contrast, gRPC C-core by default binds to a service with a Singleton lifetime.

A Scoped lifetime allows the service implementation to resolve other services with Scoped lifetimes. For example Scoped lifetime can also resolve DBContext, from the DI container through constructor injection. Using Scoped lifetime:

A new instance of the service implementation is constructed for each request.
It's not possible to share state between requests via instance members on the implementation type.
The expectation is to store shared states in a Singleton service in the DI container. The stored shared states are resolved in the constructor of the gRPC service implementation.

For more information on Scoped and Singleton lifetime, see xref:fundamentals/dependency-injection.

Add a singleton service

To facilitate the transition from gRPC C-core implementation to ASP.NET Core, it is possible to change the service lifetime of the service implementation from Scoped to Singleton. This involves adding an instance of the service implementation to the DI container:

public void ConfigureServices(IServiceCollection services)
{
    services.AddGrpc();
    services.AddSingleton(new GreeterService());
}

However, service implementation with Singleton lifetime will no longer be able to resolve Scoped services through constructor injection.

Configure gRPC services options

In C-core based apps, settings such as grpc.max_receive_message_length and grpc.max_send_message_length are configured with ChannelOption when constructing the Server instance.

In ASP.NET Core, GrpcServiceOptions provides a way to configure these settings. The settings can be applied globally to all gRPC services or to an individual service implementation type. Options specified for individual service implementation types will override global settings when configured.

public void ConfigureServices(IServiceCollection services)
{
    services
        .AddGrpc(globalOptions =>
        {
            // Global settings
            globalOptions.SendMaxMessageSize = 4096
            globalOptions.ReceiveMaxMessageSize = 4096
        })
        .AddServiceOptions<GreeterService>(greeterOptions =>
        {
            // GreeterService settings. These will override global settings
            globalOptions.SendMaxMessageSize = 2048
            globalOptions.ReceiveMaxMessageSize = 2048
        })
}

Logging

C-core based apps rely on the GrpcEnvironment to configure the logger for debugging purposes. The ASP.NET Core stack provides this functionality through the logging API. For example a logger can be added to the gRPC service via constructor injection:

public class GreeterService : Greeter.GreeterBase
{
    public GreeterService(ILogger<GreeterService> logger)
    {
    }
}

HTTPS

C-core based apps configure HTTPS through the Server.Ports property. A similar concept is used to configure servers in ASP.NET Core. For example, Kestrel uses endpoint configuration for this functionality.

Interceptors and Middlewares

ASP.NET Core middlewares offers similar functionalities compared to interceptors in C-core based gRPC apps. Middlewares and interceptors are conceptually the same as both are used to construct a pipeline that handles a gRPC request. They both allow work to be performed before or after the next component in the pipeline. However, ASP.NET Core middlewares operate on the underlying HTTP/2 messages whereas interceptors operate on the gRPC layer of abstraction using the ServerCallContext.

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