How can I horizontally scale a stateful streamable HTTP MCP server with the TypeScript SDK?
I'm building an MCP server with the TypeScript SDK and its streamable HTTP transport. To run multiple replicas behind a load balancer, I need stateful sessions to survive across instances, but stateful mode seems tied to in-memory transport state while stateless mode drops sampling, elicitation, and progress reporting. Is there a supported horizontal-scaling approach, like a Redis-backed session store?
Originally asked on GitHub: https://github.com/modelcontextprotocol/typescript-sdk/issues/843
2 answers
This is still not implemented in the TypeScript SDK. The issue was closed as a duplicate of #892, which tracks the sessionId/streamId mapping needed for stateless resumability and horizontal scaling. A contributor also noted that sessions are currently coupled to transports and that this is being discussed at the spec level, so no official fix is available yet.
The thread does not provide a supported adapter or session backend. The only concrete direction from the contributor is to implement your own version of the streamable HTTP transport, specifically the code under src/server/streamableHttp.ts in the modelcontextprotocol/typescript-sdk repository, so that you control how sessions are managed instead of relying on the default in-memory session-to-transport coupling. The socket.io Redis adapter is mentioned only as an example of the kind of design that would be needed, not as something the SDK supports.
General advice, not stated in the thread: if you cannot wait for the spec change, you would need to externalize session state yourself or otherwise handle session continuity across replicas. The thread does not discuss load balancer configuration or sticky sessions. The best way to track the official path forward is issue #892.
Did this work for you?What @KKonstantinov tried on GitHub (Outcome unclear)
A contributor suggested implementing a custom version of the streamable HTTP transport to manage sessions outside the default transport, noting that session-to-transport coupling is being discussed at the spec level. This was a suggestion and was not tested in the thread.
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