Inter-process communication with gRPC and Unix domain sockets

By James Newton-King

.NET supports inter-process communication (IPC) using gRPC. For more information about getting started with using gRPC to communicate between processes, see Inter-process communication with gRPC.

Unix domain sockets (UDS) is a widely supported IPC transport that's more efficient than TCP when the client and server are on the same machine. This article discusses how to configure gRPC communication over UDS.

Prerequisites

• .NET 5 or later
• Linux, macOS, or Windows 10/Windows Server 2019 or later

Server configuration

Unix domain sockets are supported by Kestrel, which is configured in Program.cs:

var socketPath = Path.Combine(Path.GetTempPath(), "socket.tmp");

var builder = WebApplication.CreateBuilder(args);
builder.WebHost.ConfigureKestrel(serverOptions =>
{
    serverOptions.ListenUnixSocket(socketPath, listenOptions =>
    {
        listenOptions.Protocols = HttpProtocols.Http2;
    });
});

The preceding example:

• Configures Kestrel's endpoints in ConfigureKestrel.
• Calls ListenUnixSocket to listen to a UDS with the specified path.
• Creates a UDS endpoint that isn't configured to use HTTPS. For information about enabling HTTPS, see Kestrel HTTPS endpoint configuration.

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.

Note

Some connectivity features of GrpcChannel, such as client side load balancing and channel status, can't be used together with Unix domain sockets.

Unix domain sockets connection factory example:

public class UnixDomainSocketsConnectionFactory
{
    private readonly EndPoint endPoint;

    public UnixDomainSocketsConnectionFactory(EndPoint endPoint)
    {
        this.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(this.endPoint, cancellationToken).ConfigureAwait(false);
            return new NetworkStream(socket, true);
        }
        catch
        {
            socket.Dispose();
            throw;
        }
    }
}

Using the custom connection factory to create a channel:

public static readonly string SocketPath = Path.Combine(Path.GetTempPath(), "socket.tmp");

public static GrpcChannel CreateChannel()
{
    var udsEndPoint = new UnixDomainSocketEndPoint(SocketPath);
    var connectionFactory = new UnixDomainSocketsConnectionFactory(udsEndPoint);
    var socketsHttpHandler = new SocketsHttpHandler
    {
        ConnectCallback = connectionFactory.ConnectAsync
    };

    return GrpcChannel.ForAddress("http://localhost", new GrpcChannelOptions
    {
        HttpHandler = socketsHttpHandler
    });
}

Channels created using the preceding code send gRPC calls over Unix domain sockets.