MCP server in cluster deployment not work

[JadenHuang2023]

My MCP Server is deployed in a clustered architecture, and the MCP client establishes a long connection with only one MCP server. Later, when a POST /mcp/message request is sent, it may be routed to another MCP server in the cluster.

[chemicL]

Thanks for the report. I assumed this would be a duplicate of #9 but it is a different issue entirely. I wonder whether it is a jdk-specific issue or something to discuss on the protocol level in https://github.com/modelcontextprotocol/specification

[JadenHuang2023]

@chemicL Thanks for your comments.
I only tried Java SDK, I'm not sure if other languages have the same issue.

This is indeed a real-world issue. The POST request can be sent to any server in the cluster, but that server may not have the long connection with the MCP client.
We are considering using session stickiness as a solution to address this problem firstly.

[JadenHuang2023]

It should be a protocol limitation.