Windows Communication Foundation (WCF)
At the //BUILD 2019 conference, Microsoft announced that after .NET Core 3.0 (which is due to be released in Q3 of 2019) the next major release would be called .NET 5. This is intended to prevent the extra confusion that might result from there being a .NET 4.x and a .NET Core 4.x existing in the same universe. But .NET 5 will be the evolution of .NET Core, not .NET Framework.
It seems pretty clear that the old .NET Framework is going into legacy support mode, and while Microsoft are committed to continuing to support it long into the future, with security updates and so forth, it is unlikely that there will be much innovation or development on the platform. With both WPF and Windows Forms being ported to .NET Core 3.0, and made open source like the rest of Core, the future of those technologies seems assured and the migration path should be straightforward.
What about WCF?
Windows Communication Foundation is not being ported to .NET 5, and the server-side part of WCF is not—at least, not yet—an open source technology, so currently there is no option for a community effort to fork the project and attempt to port it to .NET Core themselves.
Even if there were that option, would it be the right way to go? WCF was originally released as part of .NET Framework 3.0 at the end of 2006. The world of distributed systems was very different then: JSON was barely a thing, and Remote Procedure Calls (RPC) using XML-serialized SOAP messages was the prevailing standard for Service Oriented Architectures. The term “microservices” would not be coined for another five years. And technology moves forward ever-faster, so in the years since WCF was conceived, people have come up with better solutions to the problems it sought to solve.
Alternatives to WCF
Here are some possible alternatives for creating distributed systems, service-oriented architectures, or microservices, that are popular and well-supported today.
Basic HTTP APIs
At the simplest end, we now have basic HTTP APIs: you make a request to a URI, and it responds with data, hopefully in the format you requested (JSON, XML, etc.). This includes APIs that strictly conform with the ReST architectural style, but also simple “CRUD-over-HTTP” APIs that just use GET, PUT, POST and DELETE requests to retrieve, store and manage data. These APIs can apply security using any of the available HTTP authentication options, and can be made secure simply by applying SSL/TLS to the connection. For basic SOAP-over-HTTP or SOAP-over-TCP request/response WCF applications, an HTTP API is a good potential alternative.
HTTP APIs created with .NET Core 2.x can be documented using Swagger, which includes the ability to read the API metadata from a known endpoint and generate client library code. Visual Studio 2019 and 2017 both include support for adding “REST API” clients to a project from a Swagger URL.
Initially developed at Google, gRPC uses HTTP/2 for transport and Protocol Buffers (Protobuf) as the wire format. It is a promising drop-in replacement for some of WCF’s more complicated abilities, like full-duplex messaging over TCP. gRPC has a very similar approach to WCF in that the creator of the service declares contracts, in this case using a dedicated Interface Definition Language (IDL), from which the base code for both server and client can be generated. The “wiring up” of the service is handled in the generated code, and the developer can focus on implementing functionality in derived classes. The generated code is very efficient and takes care of serializing/deserializing data-transfer objects and processing requests and responses. Because the Protobuf serialization format is very compact, gRPC generates less network traffic than a SOAP service, or a JSON or XML HTTP API. Protobuf is also faster and more memory efficient than text-based serialization, resulting in meaningful performance and scalability gains.
gRPC also supports request/response streaming, where a client can asynchronously send a stream of requests and receive a stream of responses, which is a possible alternative to full-duplex WCF services.
In the current ASP.NET Core 3.0 preview there is already support for this code-generation step, using dotnet new grpc at the command line. The code generation step is fully integrated with the MSBuild process, and in Visual Studio 2019 the experience is almost seamless, with tooling support like syntax highlighting and IntelliSense for .proto files. Because .NET Core 3.0 is in preview, the VS2019 “New Project” wizard does not know about the grpc project type, but I expect that will come with the full release.
WebSockets / SignalR
WebSockets are an open standard for maintaining persistent connections between client and server, and sending arbitrary messages in both directions. That makes them another potential alternative for WCF’s full-duplex messaging. Although WebSockets were originally designed for browsers, they can also be used from C#, Java and other platforms.
Because WebSockets are a low-level networking solution, they are completely agnostic about the format of messages sent and received, so you can use JSON, Protobuf, MessagePack or any format you like, as long as the code at either end of the socket can parse it.
Are these long term solutions?
There are two parts to this question. First, will these protocols themselves be around for long enough to justify investing in them? And second, will Microsoft continue to provide first-class support for them?
As to the first part, HTTP and WebSockets are both standards of the Open Web, and will likely be around for a long time in one form or another (we’ve only just got onto HTTP/2.0 and HTTP/3.0 is already being worked on). gRPC and Protobuf are Google technologies and are not governed by an independent standards body, but they are well-documented and completely open source (Apache 2.0 for gRPC and BSD for Protobuf). Adoption of gRPC is sufficiently widespread and includes large enough companies that even if Google themselves stopped developing and using it, the community would continue to maintain it. SignalR is a Microsoft technology, like WCF, and so there is always the possibility that they will stop developing it at some future point. But unlike WCF, SignalR is fully open source (Apache 2.0) and could be forked and maintained by the community if necessary.
As to the second part, Microsoft seem committed to supporting popular, open technologies, and this may well mean that in the future, if a “better” alternative to something becomes available and sees widespread adoption, they might focus more development energy on that alternative. One may hope that this will be an additive approach, rather than just replacement. But in the worst case, we are talking about open source solutions which are developed in the open, rather than the proprietary, closed-source solutions of the old Microsoft. If, at some point in the future, support for a particular part of the .NET or ASP.NET framework is deprecated, a community-maintained fork of the relevant project could continue to support it.
In the end, no technology, language, framework or solution comes with a lifetime guarantee. Things get deprecated, new things arrive to replace them, and our job as developers is to try to keep up. The best we can do is look carefully at the available options, pick the one that is right for our project right now, and try to write our own business and application logic in a way that makes it as easy as possible to switch an underlying dependency out for a new one in the future. Sadly, “as easy as possible” may not always be particularly easy.