Milvus Service will not start

[bmahabirbu]

Bug description

When starting a milvus service It will say successful creation however the console.logs state that the mcp client connection was closed do to an undefined error see logs below

Operating system

Mac/Linux

Installation Method

Other

Version

next (development version)

Steps to reproduce

Start kaiden via pnpm watch

Go to the kaiden settings scroll down to the Milvus icon and create a new knowledge base.

Look at the console logs

Identify that there is no mcp associated server for milvus (an automatically spawned one should have popped up)

Relevant log output

1:36:55 PM [main] Traceback (most recent call last):
  File "/Users/bmahabir/.cache/uv/archive-v0/Jskekawu-0FbF4Aj-7Fyl/bin/mcp-server-milvus", line 6, in <module>
1:36:55 PM [main] from mcp_server_milvus.server import main
  File "/Users/bmahabir/.cache/uv/archive-v0/Jskekawu-0FbF4Aj-7Fyl/lib/python3.11/site-packages/mcp_server_milvus/server.py", line 6, in <module>
    from mcp.server.fastmcp import Context, FastMCP
ModuleNotFoundError: No module named 'mcp.server.fastmcp'
1:36:55 PM [main] MCPClientError: Connection closed
    at DefaultMCPClient.onClose (/Users/bmahabir/kaiden/packages/main/dist/index.cjs:194559:20)
    at DefaultMCPClient.transport.onclose (/Users/bmahabir/kaiden/packages/main/dist/index.cjs:193987:41)
    at MCPTransportDelegate.inner.onclose (/Users/bmahabir/kaiden/packages/main/dist/index.cjs:194611:21)
    at ChildProcess.<anonymous> (/Users/bmahabir/kaiden/packages/main/dist/index.cjs:73562:23)
    at ChildProcess.emit (node:events:508:28)
    at maybeClose (node:internal/child_process:1101:16)
    at Socket.<anonymous> (node:internal/child_process:457:11)
    at Socket.emit (node:events:508:28)
    at Pipe.<anonymous> (node:net:346:12) {
  cause: undefined,
  data: undefined,
  code: undefined,
  statusCode: undefined,
  url: undefined,
  responseBody: undefined,
  Symbol(vercel.ai.error): true,
  Symbol(vercel.ai.error.AI_MCPClientError): true
}

Additional context

The fix

extensions/milvus/src/api/milvus-connection.ts

           {
             registryType: 'pypi',
             identifier: 'mcp-server-milvus',
             version: '0.1.1.dev8',
  -          runtimeHint: 'python',
  +          runtimeHint: 'uvx',
             transport: {
               type: 'stdio',
             },
            // mcp-server-milvus imports mcp.server.fastmcp, which was removed when the
            // mcp SDK released 2.0.0. Pin the last compatible 1.x release explicitly.
            runtimeArguments: [
              {
                isRequired: true,
                format: 'string',
                value: '--with',
                isSecret: false,
              },
              {
  
              isRequired: true,
  
              format: 'string',
                value: 'mcp==1.29.0',
                isSecret: false,
              },
            ],
             packageArguments: [
               {
                 isRequired: true,
                 format: 'string',
                 value: '--milvus-uri',
                 isSecret: false,
               },

Issue: the new FastMCP package 2.0 does not contain mcp.server.fastmcp imports due to understandable changed to a version 2.0! The fix is to tag the package to 1.29.0. A follow up would be to update the code to work with 2.0

[coderabbitai]

🔗 Related PRs

#1350 - fix: ensure Milvus MCP servers are unique [merged]

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[fullsend-ai-triage]

🤖 Finished Triage · ✅ Success · Started 5:57 PM UTC · Completed 6:00 PM UTC
Commit: 6725fc0 · View workflow run →

[fullsend-ai-triage]

Triage Summary

Severity: High — Milvus knowledge base creation is completely broken.

Root Cause: The mcp-server-milvus package (v0.1.1.dev8) depends on mcp.server.fastmcp, which was removed in MCP SDK 2.0.0. The current configuration in extensions/milvus/src/api/milvus-connection.ts has two issues:

1. runtimeHint is set to 'python' instead of 'uvx', which prevents proper package isolation
2. No runtimeArguments are specified to pin the MCP SDK version, so the incompatible 2.0+ version gets installed

Recommended Fix:

In extensions/milvus/src/api/milvus-connection.ts, update the package configuration:

• Change runtimeHint from 'python' to 'uvx'
• Add runtimeArguments to pin mcp==1.29.0 (the last compatible 1.x release)

// Proposed test case
// Verify MilvusConnection registers MCP server with correct runtime configuration
test('should register MCP server with uvx runtime and pinned mcp SDK', () => {
  const registerSpy = vi.mocked(api.mcpRegistry.registerServer);
  new MilvusConnection('/path', 'test-db', 'container-1', 19530, true);

  const serverDetail = registerSpy.mock.calls[0][0];
  expect(serverDetail.packages[0].runtimeHint).toBe('uvx');
  expect(serverDetail.packages[0].runtimeArguments).toEqual(
    expect.arrayContaining([
      expect.objectContaining({ value: '--with' }),
      expect.objectContaining({ value: 'mcp==1.29.0' }),
    ]),
  );
});

Follow-up: A separate issue should track updating mcp-server-milvus to be compatible with MCP SDK 2.0, which would remove the need for version pinning.

---

Labels: This is a confirmed bug in the MCP integration layer of the Milvus extension. The 'area/mcp' label applies because the root cause is MCP SDK version incompatibility. The 'bug' and 'area/rag' labels are already applied.

[fullsend-ai-coder]

🤖 Finished Code · ✅ Success · Started 6:01 PM UTC · Completed 6:21 PM UTC
Commit: 6725fc0 · View workflow run →