[Bug]: Starting the mobgodb-mcp-server fails due to connection error

[rallepalle]

App

• Cursor
• Windsurf
• VSCode
• VSCode Insiders
• Claude Desktop
• Other

Affected Models (if applicable)

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

Bug Description

I started the mobgodb-mcp-server with the following settings: npx -y mongodb-mcp-server
The environment variable is set: MDB_MCP_CONNECTION_STRING=mongodb://localhost:30017/vpc

Unfortunately, the app tries to connect to MongoDB via the default port 27017, but my MongoDB is accessible via port 30017 (locally within Kubernetes).

I do not need username and pw for the local connection as no credentials are stored. Connection with e.g. MongoDB Compass or other applications works without any problems.

Failed to connect to MongoDB instance using the connection string from the config: MongoNetworkError: connect ECONNREFUSED 127.0.0.1:27017 at Socket.<anonymous> (/Users/FOOBAR/.npm/_npx/191c568aa03d4fb8/node_modules/mongodb/lib/cmap/connect.js:285:44) at Object.onceWrapper (node:events:622:26) at Socket.emit (node:events:507:28) 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:1634:16) { errno: -61, 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"}

[blva]

Hi @rallepalle, thanks for reporting this issue!

I'm not able to reproduce it defaulting to 27017, perharps you had this default value configured somehow?

I think you might get this working if you try to export the env variable, here's my example:

export MDB_MCP_CONNECTION_STRING=mongodb://localhost:30017/vpc

npx -y mongodb-mcp-server
Failed to connect to MongoDB instance using the connection string from the config:  MongoNetworkError: connect ECONNREFUSED 127.0.0.1:30017, connect ECONNREFUSED ::1:30017
    at Socket.<anonymous> (/Users/<redacted>/.npm/_npx/191c568aa03d4fb8/node_modules/mongodb/lib/cmap/connect.js:285:44)
    at Object.onceWrapper (node:events:622:26)
    at Socket.emit (node:events:507:28)
    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]: AggregateError [ECONNREFUSED]:
      at internalConnectMultiple (node:net:1139:18)
      at afterConnectMultiple (node:net:1714:7) {
    code: 'ECONNREFUSED',
    [errors]: [ [Error], [Error] ]
  }
}
{"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"}

note that the error correctly points to the expected port:MongoNetworkError: connect ECONNREFUSED 127.0.0.1:30017, connect ECONNREFUSED ::1:30017

Could you please try exporting and let me know if that works for you? Thanks!

[rallepalle]

Hi @blva , thanks for your answer! I did exactly what you suggested, but same error
~ % export MDB_MCP_CONNECTION_STRING=mongodb://localhost:30017/vpc
~ % npx -y mongodb-mcp-server

Failed to connect to MongoDB instance using the connection string from the config: MongoNetworkError: connect ECONNREFUSED 127.0.0.1:27017 at Socket.<anonymous> (/Users/WEYERSR/.npm/_npx/191c568aa03d4fb8/node_modules/mongodb/lib/cmap/connect.js:285:44) at Object.onceWrapper (node:events:622:26) at Socket.emit (node:events:507:28) 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:1634:16) { errno: -61, code: 'ECONNREFUSED', syscall: 'connect', address: '127.0.0.1', port: 27017 } }

[T800Terminator]

platform: Trae

error:
npm WARN deprecated node-domexception@1.0.0: Use your platform's native DOMException instead
file:///Users/mingfangwu/.npm/_npx/191c568aa03d4fb8/node_modules/mongodb-mcp-server/dist/packageInfo.js:1
import packageJson from "../package.json" with { type: "json" };
^^^^

SyntaxError: Unexpected token 'with'
at DefaultModuleLoader.moduleStrategy (node:internal/modules/esm/translators:116:18)
at DefaultModuleLoader.moduleProvider (node:internal/modules/esm/loader:203:14)

Node.js v20.3.0

[blva]

Hi, to get a bit more info to see if I can reproduce:

1. What's the OS + Arch you're running this from?
2. To double-check this is related to env variables only, are you able to get this working if you pass CLI arguments?
3. What do you get if you set the connection string with mongodb://localhost:30017/vpc?directConnection=true