Fix: Unknown SSE Event Keepalive With Virtual Servers

Introduction

Hey guys! Ever encountered the frustrating "Unknown SSE event: keepalive" error when diving into the world of virtual servers, especially with tools like MCP (MCP-Context-Forge)? I recently ran into this issue while working with a locally hosted MCP server, and I wanted to share my journey in troubleshooting it. If you're scratching your head over this error, you're in the right place. Let's break it down together and figure out how to solve it!

This article dives deep into resolving the “Unknown SSE event: keepalive” error encountered while using virtual servers with MCP. We'll explore the initial setup, the problem arising when connecting to virtual servers, and potential solutions to get your development environment running smoothly. Whether you're an experienced developer or just starting, this guide will provide valuable insights into debugging and fixing this common issue.

Initial Setup and the First Success

So, I started by creating two virtual servers from my locally hosted MCP server. Think of it like dividing a pie into slices – I split four tools across these two virtual servers. My original MCP server URL looked something like this: http://localhost:8005/sse. I could see the tools, access them, and even call them without any hiccups.

To interact with the server, I used a Python script with the fastmcp library. The initial code looked like this:

import asyncio
from fastmcp import Client, FastMCP

client = Client("http://localhost:8005/sse")

async def main():
    async with client:
        # Basic server interaction
        await client.ping()
        
        # List available operations
        tools = await client.list_tools()
        resources = await client.list_resources()
        prompts = await client.list_prompts()

        print("Available tools:")
        for tool in tools:
            print(tool.name)
        print()
        
        # Execute operations
        result = await client.call_tool("add", {"a": 1, "b": 2})
        print("Addition of 1 + 2:")
        print(result.content[0].text)

        # Execute operations
        result = await client.call_tool("subtract", {"a": 1, "b": 2})
        print("Subtraction of 1 - 2:")
        print(result.content[0].text)

asyncio.run(main())

This script was my initial victory! It successfully connected to the main server, listed the available tools, and even performed some basic operations like addition and subtraction. Everything seemed to be working perfectly, which was a great confidence booster.

The Problem: