Fixing Unknown SSE Event Keepalive In MCP Virtual Servers

Aug 9, 2025 by Mei Lin 58 views

Getting Unknown SSE Event Keepalive When Trying to Use Virtual Servers

Introduction

Hey guys! Ever run into the Unknown SSE event: keepalive error when trying to connect to virtual servers? It can be super frustrating, especially when your initial setup works perfectly fine. This article will dive into a common scenario where this happens, specifically when using fastmcp with IBM's MCP (Meta-Compute Platform) context forge. We'll break down the problem, look at the code snippets involved, and explore potential solutions to get your virtual servers humming. So, let's get started and debug this issue together!

Background: MCP and Virtual Servers

Before we jump into the code, let's briefly discuss what MCP and virtual servers are in this context. MCP, or Meta-Compute Platform, is a system that allows you to manage and orchestrate various tools and resources. Think of it as a central hub for your computational tasks. Virtual servers, in this case, are like isolated environments within the MCP, each potentially having access to a subset of the available tools. This is super useful for organizing your work and ensuring that different tasks don't interfere with each other. Essentially, it's like having multiple computers within one system.

Understanding Server-Sent Events (SSE)

The error message we are encountering involves SSE, or Server-Sent Events. SSE is a communication protocol that allows a server to push data to a client over a single HTTP connection. This is particularly useful for real-time updates, like status notifications or data streams. The "keepalive" event is a common mechanism used in SSE to ensure that the connection remains open, even when there's no other data being transmitted. So, when we see "Unknown SSE event: keepalive," it indicates that the client (in our case, the fastmcp library) isn't properly handling these keepalive messages, which can lead to connection issues. This is why understanding SSE is crucial for troubleshooting our problem. If the client fails to process these keepalive messages, the connection might be dropped, or other unexpected behavior could occur.

The Scenario: Local MCP Server vs. Virtual Servers

The core issue arises when switching from connecting to a locally hosted MCP server to connecting to virtual servers within that MCP. Initially, the user set up a local MCP server, divided four tools among two virtual servers, and successfully interacted with it. They were able to list tools and call them directly using the fastmcp library. However, when they attempted to connect to a specific virtual server using its URL and a token for authentication, they started encountering the dreaded Unknown SSE event: keepalive messages. This suggests that while the basic connection to the MCP server is working, there's something different about how virtual servers handle SSE or how the fastmcp client interacts with them.

Code Snippet 1: Working with the Local MCP Server

Let's examine the first code snippet, which works flawlessly with the local MCP server:

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 code snippet demonstrates a basic interaction with the MCP server. It initializes a Client object with the server's URL, pings the server to check the connection, lists available tools, and then calls two tools (add and subtract) to perform simple arithmetic operations. The key takeaway here is that this code works perfectly, indicating that the fundamental setup and communication with the MCP server are functional.

Code Snippet 2: Encountering the Error with Virtual Servers

Now, let's look at the second code snippet, which produces the Unknown SSE event: keepalive error:

import asyncio
from fastmcp import Client, FastMCP
from fastmcp.client.auth import BearerAuth

client = Client("http://localhost:4444/servers/2/sse", auth="<token>")


async def main():
    async with client:

        await client.ping()

        # List available operations
        tools = await client.list_tools()
        # resources = await client.list_resources()
        # prompts = await client.list_prompts()

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

asyncio.run(main())

This code snippet is very similar to the first one, but with a crucial difference: it's connecting to a specific virtual server (http://localhost:4444/servers/2/sse) and using authentication (auth="<token>"). The Unknown SSE event: keepalive error appears when running this code, suggesting that the issue is related to either the virtual server endpoint, the authentication mechanism, or a combination of both. The introduction of authentication using a token could be a significant factor, as it might be affecting how the server sends SSE messages or how the client interprets them.

Diagnosing the Problem: Key Differences and Potential Causes

So, what's causing this issue? Let's break down the key differences between the two scenarios and explore potential causes:

Endpoint URL: The first code snippet connects to http://localhost:8005/sse, while the second connects to http://localhost:4444/servers/2/sse. This suggests that the virtual server endpoint might have different SSE handling characteristics compared to the main MCP server endpoint.
Authentication: The second code snippet uses authentication (auth="<token>"), while the first one doesn't. Authentication can introduce complexities in how SSE connections are established and maintained. The server might be sending keepalive messages differently when authentication is involved.
fastmcp Client Behavior: It's possible that the fastmcp library isn't correctly handling keepalive events when connected to a virtual server with authentication. This could be a bug in the library or a configuration issue.

Potential Causes in Detail

SSE Implementation Differences: Virtual servers within MCP might have a slightly different implementation of SSE compared to the main server. This could include variations in how keepalive messages are sent or formatted.
Authentication and SSE: The authentication middleware might be interfering with the SSE connection or the handling of keepalive messages. For example, the server might be sending keepalive messages in a format that the fastmcp client doesn't expect when authentication is enabled.
fastmcp Library Bug: There might be a bug in the fastmcp library that causes it to misinterpret or ignore keepalive messages in certain scenarios, such as when connecting to virtual servers with authentication.
Network Issues: Although less likely in a local setup, network issues could potentially cause SSE connections to be dropped or keepalive messages to be lost.
Server Configuration: The MCP server itself might have specific configurations for virtual servers that affect SSE behavior. This could include settings related to connection timeouts or keepalive intervals.

Troubleshooting Steps and Potential Solutions

Now that we've identified the potential causes, let's explore some troubleshooting steps and potential solutions:

Verify Authentication: Ensure that the token being used for authentication is valid and has the necessary permissions to access the virtual server. A common mistake is using an expired token or one that doesn't have the correct scope.
Inspect Network Traffic: Use tools like Wireshark or the browser's developer tools to inspect the network traffic between the client and the server. This can help you see the raw SSE messages being exchanged, including the keepalive events. Look for any inconsistencies or errors in the messages.
Update fastmcp Library: Check if there's a newer version of the fastmcp library available. Newer versions often include bug fixes and improvements that could address the issue. You can update the library using pip:
```
pip install --upgrade fastmcp
```
Implement Custom SSE Handling: If the fastmcp library doesn't handle keepalive events correctly, you might need to implement custom SSE handling using a library like aiohttp or sseclient-py. This would involve manually parsing the SSE stream and handling keepalive messages.
Check Server Logs: Examine the MCP server logs for any errors or warnings related to SSE connections or authentication. The logs might provide valuable clues about what's going wrong.
Simplify the Code: Try simplifying the code to isolate the issue. For example, remove the call_tool part and just focus on connecting to the server and listing tools. This can help determine if the problem is related to tool execution or the initial connection.
Contact MCP Support: If you're using a managed MCP service, consider contacting their support team. They might be aware of the issue or have specific configurations that need to be adjusted.

Example of Custom SSE Handling (Conceptual)

Here's a conceptual example of how you might implement custom SSE handling using aiohttp:

import asyncio
import aiohttp

async def handle_sse_events(url, token):
    async with aiohttp.ClientSession() as session:
        headers = {"Authorization": f"Bearer {token}"}
        async with session.get(url, headers=headers) as response:
            async for line in response.content.iter_any():
                if line:
                    line = line.decode("utf-8").strip()
                    if line.startswith("event: keepalive"):
                        print("Received keepalive")
                    elif line.startswith("data:"):
                        data = line[5:].strip()
                        print(f"Received data: {data}")

async def main():
    await handle_sse_events("http://localhost:4444/servers/2/sse", "<token>")

asyncio.run(main())

This code snippet demonstrates how to use aiohttp to establish an SSE connection, read the stream line by line, and handle keepalive events and data messages. This is a more advanced approach but gives you fine-grained control over the SSE connection.

Conclusion

The Unknown SSE event: keepalive error can be a tricky one to tackle, but by understanding the underlying concepts of SSE, MCP, and virtual servers, we can systematically diagnose and address the issue. Remember to verify your authentication, inspect network traffic, update your libraries, and consider custom SSE handling if necessary. By following these steps, you'll be well on your way to getting your virtual servers up and running smoothly. Keep experimenting, keep debugging, and don't hesitate to reach out to the community or support channels for help. Happy coding, guys!