[Bug]: Failed to connect to ReplicaSet

[plutonji]

Version

0.1.1

App

• Cursor
• Windsurf
• VSCode
• VSCode Insiders
• Claude Desktop
• Cherry Studio

Affected Models (if applicable)

• Claude 3.5 Sonnet
• Claude 3.7 Sonnet
• GPT-4a
• o4-mini
• Other

Bug Description

With environment MDP_MCP_CONNECTION_STRING value as below:

MDB_MCP_CONNECTION_STRING=mongodb://user:pass@mongodb1:27017,mongodb2:27017,mongodb3:27017/platform

I got the error:

[blva]

thanks for reporting the issue @plutonji , could you please share the MCP server logs? the logs location is described here https://github.com/mongodb-js/mongodb-mcp-server?tab=readme-ov-file#log-path

[himanshusinghs]

Hi @plutonji 👋 Just a quick follow up about the MCP server logs so that we can dig deeper into the problem.

[mmitchell88]

I also have a problem connecting to a replica set. Connecting to a non replica set works fine but for my production replica set it changes my IP and fails

echo '{"jsonrpc": "2.0", "id": 1, "method": "initialize", "params": {"protocolVersion": "2024-11-05"}}' | docker run --rm -i --network host -e MDB_MCP_CONNECTION_STRING="mongodb://user:password@10.0.0.210:27017/production" mongodb/mongodb-mcp-server:latest 2>&1 | tee /tmp/mcp_prod.log

My log output is as follows

{"jsonrpc":"2.0","id":1,"error":{"code":-32603,"message":"[\n  {\n    \"code\": \"invalid_type\",\n    \"expected\": \"object\",\n    \"received\": \"undefined\",\n    \"path\": [\n      \"params\",\n      \"capabilities\"\n    ],\n    \"message\": \"Required\"\n  },\n  {\n    \"code\": \"invalid_type\",\n    \"expected\": \"object\",\n    \"received\": \"undefined\",\n    \"path\": [\n      \"params\",\n      \"clientInfo\"\n    ],\n    \"message\": \"Required\"\n  }\n]"}}
Failed to connect to MongoDB instance using the connection string from the config:  MongoNetworkError: connect ECONNREFUSED 127.0.0.1:27017
    at Socket.<anonymous> (/usr/local/lib/node_modules/mongodb-mcp-server/node_modules/mongodb/lib/cmap/connect.js:286:44)
    at Object.onceWrapper (node:events:633:26)
    at Socket.emit (node:events:518:28)
    at emitErrorNT (node:internal/streams/destroy:170:8)
    at emitErrorCloseNT (node:internal/streams/destroy:129:3)
    at process.processTicksAndRejections (node:internal/process/task_queues:90:21) {
  errorLabelSet: Set(1) { 'ResetPool' },
  beforeHandshake: false,
  [cause]: Error: connect ECONNREFUSED 127.0.0.1:27017
      at TCPConnectWrap.afterConnect [as oncomplete] (node:net:1636:16) {
    errno: -111,
    code: 'ECONNREFUSED',
    syscall: 'connect',
    address: '127.0.0.1',
    port: 27017
  }
}
{"method":"notifications/message","params":{"level":"emergency","data":"[server]: Fatal error running server: Error: Failed to connect to MongoDB instance using the connection string from the config"},"jsonrpc":"2.0"}

[himanshusinghs]

Hi @mmitchell88! Thank you for the logs.

A few further clarifications please:

1. When you use the same connection string to connect via mongosh, does it work?
2. Is it a locally deployed replica set or Atlas deployed replica set?
3. If it is a locally deployed replica set, are you using docker to deploy it? If yes, can you please confirm that all the replica set members are on the same docker network?
4. How are you running the mcp-server? Which client are you using to connect with it and what is the configuration? (Leave the sensitive data out when posting the config.)

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