Asp.net core server shutdown - disconnect or notify connected MCP clients

[codeape2]

I am using the ASP.NET Core extensions for the MCP C# SDK to implement tools and resources in an existing web application - works great!

In development, I sometimes frequently restart the ASP.NET Core process. Before adding the MCP server to the application, an application restart was instant.

If I have a MCP test client connected to the server (for instance npx @modelcontextprotocol/inspector) then shutting down the asp.net core process takes some time (~15 seconds or so). I assume this is because the connected MCP client has a streaming HTTP connection open to the server, and this somehow interferes with the normal shut-down process.

Questions:

• Is there a way to hook in to the asp.net shutdown process and disconnect the MCP clients?
• Does the MCP protocol define how this should be handled? (i.e. a way for the server to tell the clients you-will-be-disconnected-and-can-likely-reconnect-in-five-seconds)?

[halter73]

Is there a way to hook in to the asp.net shutdown process and disconnect the MCP clients?

You can minimize the impact of the slow shutdown by lowering the Host ShutdownTimeout from its default of 30 seconds to something smaller like 5 seconds or 1 second.

var builder = WebApplication.CreateBuilder(args);
//...
builder.WebHost.UseShutdownTimeout(TimeSpan.FromSeconds(1));
//...
var app = builder.Build();

Upon shutdown, this will give all requests only 1 second for middleware and request handlers to complete before aborting them. This could be undesirable if you application has a tool call that can take longer than that. That's why the default is a full 30 seconds, but it might not matter for testing with npx @modelcontextprotocol/inspector in development.

#843 that should properly fix it by closing the known long-running SSE GET request made by MCP clients using the Streamable HTTP request at the beginning of the shutdown process, but allowing other requests like POST tool calls to delay shutdown until they complete.

Does the MCP protocol define how this should be handled? (i.e. a way for the server to tell the clients you-will-be-disconnected-and-can-likely-reconnect-in-five-seconds)?

It provides some guidance. The specification says the following:

• The server MAY close the SSE stream at any time.

3. The server MAY terminate the session at any time, after which it MUST respond to requests containing that session ID with HTTP 404 Not Found.

https://modelcontextprotocol.io/specification/2025-06-18/basic/transports#session-management

And unless you're using Stateless mode which no longer has a concept of a session, this is what will happen when you restart the server. It's just without the fix in #843 or dramatically shortening the shutdown timeout, this takes too long right now.

[codeape2]

Thanks for the explanation and the code change!