New gRPC inter-process doc (#19891)

Author: JamesNK

aspnetcore/grpc/interprocess.md

@@ -0,0 +1,106 @@
+---
+title: Inter-process communication with gRPC
+author: jamesnk
+description: Learn how to use gRPC for inter-process communication.
+monikerRange: '>= aspnetcore-5.0'
+ms.author: jamesnk
+ms.date: 09/16/2020
+no-loc: ["ASP.NET Core Identity", cookie, Cookie, Blazor, "Blazor Server", "Blazor WebAssembly", "Identity", "Let's Encrypt", Razor, SignalR]
+uid: grpc/interprocess
+---
+# Inter-process communication with gRPC
+
+By [James Newton-King](https://twitter.com/jamesnk)
+
+gRPC calls between a client and service are usually sent over TCP sockets. TCP was designed for communicating across a network. [Inter-process communication (IPC)](https://wikipedia.org/wiki/Inter-process_communication) is more efficient than TCP when the client and service are on the same machine. This document explains how to use gRPC with custom transports in IPC scenarios.
+
+## Server configuration
+
+Custom transports are supported by [Kestrel](xref:fundamentals/servers/kestrel). Kestrel is configured in *Program.cs*:
+
+```csharp
+public static readonly string SocketPath = Path.Combine(Path.GetTempPath(), "socket.tmp");
+
+public static IHostBuilder CreateHostBuilder(string[] args) =>
+    Host.CreateDefaultBuilder(args)
+        .ConfigureWebHostDefaults(webBuilder =>
+        {
+            webBuilder.UseStartup<Startup>();
+            webBuilder.ConfigureKestrel(options =>
+            {
+                if (File.Exists(SocketPath))
+                {
+                    File.Delete(SocketPath);
+                }
+                options.ListenUnixSocket(SocketPath);
+            });
+        });
+```
+
+The preceding example:
+
+* Configures Kestrel's endpoints in `ConfigureKestrel`.
+* Calls <xref:Microsoft.AspNetCore.Server.Kestrel.Core.KestrelServerOptions.ListenUnixSocket*> to listen to a [Unix domain socket (UDS)](https://wikipedia.org/wiki/Unix_domain_socket) with the specified path.
+
+Kestrel has built-in support for UDS endpoints. UDS are supported on Linux, macOS and [modern versions of Windows](https://devblogs.microsoft.com/commandline/af_unix-comes-to-windows/).
+
+## Client configuration
+
+`GrpcChannel` supports making gRPC calls over custom transports. When a channel is created, it can be configured with a `SocketsHttpHandler` that has a custom `ConnectCallback`. The callback allows the client to make connections over custom transports and then send HTTP requests over that transport.
+
+> [!IMPORTANT]
+> `SocketsHttpHandler.ConnectCallback` is a new API in .NET 5 release candidate 2.
+
+Unix domain sockets connection factory example:
+
+```csharp
+public class UnixDomainSocketConnectionFactory
+{
+    private readonly EndPoint _endPoint;
+
+    public UnixDomainSocketConnectionFactory(EndPoint endPoint)
+    {
+        _endPoint = endPoint;
+    }
+
+    public async ValueTask<Stream> ConnectAsync(SocketsHttpConnectionContext _,
+        CancellationToken cancellationToken = default)
+    {
+        var socket = new Socket(AddressFamily.Unix, SocketType.Stream, ProtocolType.Unspecified);
+
+        try
+        {
+            await socket.ConnectAsync(_endPoint, cancellationToken).ConfigureAwait(false);
+            return new NetworkStream(socket, true);
+        }
+        catch
+        {
+            socket.Dispose();
+            throw;
+        }
+    }
+}
+```
+
+Using the custom connection factory to create a channel:
+
+```csharp
+public static readonly string SocketPath = Path.Combine(Path.GetTempPath(), "socket.tmp");
+
+public static GrpcChannel CreateChannel()
+{
+    var udsEndPoint = new UnixDomainSocketEndPoint(SocketPath);
+    var connectionFactory = new UnixDomainSocketConnectionFactory(udsEndPoint);
+    var socketsHttpHandler = new SocketsHttpHandler
+    {
+        ConnectionFactory = connectionFactory.ConnectAsync
+    };
+
+    return GrpcChannel.ForAddress("http://localhost", new GrpcChannelOptions
+    {
+        HttpHandler = socketsHttpHandler
+    });
+}
+```
+
+Channels created using the preceding code send gRPC calls over Unix domain sockets. Support for other IPC technologies can be implemented using the extensibility in Kestrel and `SocketsHttpHandler`.

aspnetcore/grpc/performance.md

@@ -106,6 +106,12 @@ There are many L7 proxies available. Some options are:
 
 ::: moniker range=">= aspnetcore-5.0"
 
+## Inter-process communication
+
+gRPC calls between a client and service are usually sent over TCP sockets. TCP is great for communicating across a network, but [inter-process communication (IPC)](https://wikipedia.org/wiki/Inter-process_communication) is more efficient when the client and service are on the same machine.
+
+Consider using a transport like Unix domain sockets or named pipes for gRPC calls between processes on the same machine. For more information, see <xref:grpc/interprocess>.
+
 ## Keep alive pings
 
 Keep alive pings can be used to keep HTTP/2 connections alive during periods of inactivity. Having an existing HTTP/2 connection ready when an app resumes activity allows for the initial gRPC calls to be made quickly, without a delay caused by the connection being reestablished.

aspnetcore/toc.yml

@@ -740,6 +740,10 @@
       uid: grpc/security
     - name: Performance best practices
       uid: grpc/performance
+    - name: Inter-process communication
+      uid: grpc/interprocess
+    - name: Create JSON Web APIs from gRPC
+      uid: grpc/httpapi
     - name: Manage Protobuf references with dotnet-grpc
       uid: grpc/dotnet-grpc
     - name: Test services with gRPC tools
@@ -750,8 +754,6 @@
       uid: grpc/wcf
     - name: Compare gRPC services with HTTP APIs
       uid: grpc/comparison
-    - name: Create JSON Web APIs from gRPC
-      uid: grpc/httpapi
     - name: Samples
       href: https://github.com/grpc/grpc-dotnet/tree/master/examples
     - name: Troubleshoot